What s the best way to trim std string

Question

I m currently using the following code to right-trim all the std  strings in my programs   std  string s  s erase s find last not of    n r t   1     It works fine  but I wonder if there are some end-cases where it might fail   Of course  answers with elegant alternatives and also left-trim solution are welcome

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Using Boost s string algorithms would be easiest    include  lt boost algorithm string hpp gt   std  string str  hello world      boost  trim right str     str is now  hello world    There s also trim left and trim  which trims both sides     If you add  copy suffix to any of above function names e g  trim copy  the function will return a trimmed copy of the string instead of modifying it through a reference   If you add  if suffix to any of above function names e g  trim copy if  you can trim all characters satisfying your custom predicate  as opposed to just whitespaces

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With C  11 also came a regular expression module  which of course can be used to trim leading or trailing spaces   Maybe something like this   std  string ltrim const std  string amp  s        static const std  regex lws      space       std  regex constants  extended       return std  regex replace s  lws          std  string rtrim const std  string amp  s        static const std  regex tws     space        std  regex constants  extended       return std  regex replace s  tws          std  string trim const std  string amp  s        return ltrim rtrim s

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Hacked off of Cplusplus com  std  string choppa const std  string  amp t  const std  string  amp ws        std  string str   t      size t found      found   str find last not of ws       if  found    std  string  npos          str erase found 1       else         str clear                  str is all whitespace      return str      This works for the null case as well   -

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I guess if you start asking for the  best way  to trim a string  I d say a good implementation would be one that    Doesn t allocate temporary strings Has overloads for in-place trim and copy trim Can be easily customized to accept different validation sequences   logic   Obviously there are too many different ways to approach this and it definitely depends on what you actually need  However  the C standard library still has some very useful functions in  lt string h gt   like memchr  There s a reason why C is still regarded as the best language for IO - its stdlib is pure efficiency   inline const char  trim start const char  str        while  memchr    t n r    str  4      str      return str    inline const char  trim end const char  end        while  memchr    t n r   end -1   4   --end      return end    inline std  string trim const char  buffer  int len     trim a buffer  input         return std  string trim start buffer   trim end buffer   len      inline void trim inplace std  string amp  str        str assign trim start str c str             trim end str c str     str length         int main         char str        t  nhello r  t  n        string trimmed   trim str  strlen str        cout  lt  lt       lt  lt  trimmed  lt  lt       lt  lt  endl       system  pause        return 0

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Trims both ends  string trim const std  string  amp str       string result    quot  quot       size t endIndex   str size        while  endIndex  gt  0  amp  amp  isblank str endIndex-1            endIndex -  1      for  size t i 0  i lt endIndex   i  1           char ch   str i           if   isblank ch     result size   gt 0              result    ch           return result

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Use the following code to right trim  trailing  spaces and tab characters from std  strings  ideone       trim trailing spaces size t endpos   str find last not of    t    size t startpos   str find first not of    t    if  std  string  npos    endpos         str   str substr  0  endpos 1        str   str substr  startpos      else       str erase std  remove std  begin str   std  end str         std  end str        And just to balance things out  I ll include the left trim code too  ideone       trim leading spaces size t startpos   str find first not of    t    if  string  npos    startpos         str   str substr  startpos

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Here is my version   size t beg   s find first not of    r n    return  beg    string  npos         in substr beg  s find last not of    r n   - beg

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Poor man s string trim  spaces only   std  string trimSpaces const std  string amp  str        int start  len           for  start   0  start  lt  str size    amp  amp  str start          start         for  len   str size   - start  len  gt  0  amp  amp  str start   len - 1          len--            return str substr start  len

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Trim C  11 implementation   static void trim std  string  amp s         s erase s begin    std  find if not s begin    s end       char c   return std  isspace c             s erase std  find if not s rbegin    s rend       char c   return std  isspace c      base    s end

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Use the following code to right trim  trailing  spaces and tab characters from std  strings  ideone       trim trailing spaces size t endpos   str find last not of    t    size t startpos   str find first not of    t    if  std  string  npos    endpos         str   str substr  0  endpos 1        str   str substr  startpos      else       str erase std  remove std  begin str   std  end str         std  end str        And just to balance things out  I ll include the left trim code too  ideone       trim leading spaces size t startpos   str find first not of    t    if  string  npos    startpos         str   str substr  startpos

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I have read most of the answers but did not found anyone making use of istringstream  std  string text    quot Let me split this into words quot    std  istringstream iss text   std  vector lt std  string gt  results  std  istream iterator lt std  string gt  iss                                     std  istream iterator lt std  string gt       The result is vector of words and it can deal with the strings having internal whitespace too  Hope this helped

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This can be done more simply in C  11 due to the addition of back   and pop back     while    s empty    amp  amp  isspace s back      s pop back

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Try this  it works for me   inline std  string trim std  string amp  str        str erase 0  str find first not of                prefixing spaces     str erase str find last not of      1             surfixing spaces     return str

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This any good    Cause this post totally needs another answer     string trimBegin string str        string whites     t r n        int i   0      while  whites find str i        whites  npos       str erase 0  i       return str      Similar case for the trimEnd  just reverse the polari- er  indices

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As I wanted to update my old C   trim function with a C   11 approach I have tested a lot of the posted answers to the question  My conclusion is that I keep my old C   solution    It is the fastest one by large  even adding more characters to check  e g   r n I see no use case for  f v  is still faster than the solutions using algorithm   std  string  amp  trimMe  std  string  amp  str          right trim    while  str length     gt  0  amp  amp   str  str length   -1            str  str length   -1       t          str erase  str length   -1  1          left trim    while  str length     gt  0  amp  amp   str  0            str  0       t          str erase  0  1      return str

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Use the following code to right trim  trailing  spaces and tab characters from std  strings  ideone       trim trailing spaces size t endpos   str find last not of    t    size t startpos   str find first not of    t    if  std  string  npos    endpos         str   str substr  0  endpos 1        str   str substr  startpos      else       str erase std  remove std  begin str   std  end str         std  end str        And just to balance things out  I ll include the left trim code too  ideone       trim leading spaces size t startpos   str find first not of    t    if  string  npos    startpos         str   str substr  startpos

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I guess if you start asking for the  best way  to trim a string  I d say a good implementation would be one that    Doesn t allocate temporary strings Has overloads for in-place trim and copy trim Can be easily customized to accept different validation sequences   logic   Obviously there are too many different ways to approach this and it definitely depends on what you actually need  However  the C standard library still has some very useful functions in  lt string h gt   like memchr  There s a reason why C is still regarded as the best language for IO - its stdlib is pure efficiency   inline const char  trim start const char  str        while  memchr    t n r    str  4      str      return str    inline const char  trim end const char  end        while  memchr    t n r   end -1   4   --end      return end    inline std  string trim const char  buffer  int len     trim a buffer  input         return std  string trim start buffer   trim end buffer   len      inline void trim inplace std  string amp  str        str assign trim start str c str             trim end str c str     str length         int main         char str        t  nhello r  t  n        string trimmed   trim str  strlen str        cout  lt  lt       lt  lt  trimmed  lt  lt       lt  lt  endl       system  pause        return 0

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Here s a solution easy to understand for beginners not used to write std   everywhere and not yet familiar with const-correctness  iterators  STL algorithms  etc      include  lt string gt   include  lt cctype gt     for isspace using namespace std       Left trim the given string     hello     -- gt   hello      string left trim string str        int numStartSpaces   0      for  int i   0  i  lt  str length    i              if   isspace str i    break          numStartSpaces              return str substr numStartSpaces         Right trim the given string     hello     -- gt     hello    string right trim string str        int numEndSpaces   0      for  int i   str length   - 1  i  gt   0  i--            if   isspace str i    break          numEndSpaces              return str substr 0  str length   - numEndSpaces         Left and right trim the given string     hello     -- gt   hello    string trim string str        return right trim left trim str        Hope it helps

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It seems I m really late to the party - I can t believe this was asked 7 years ago    Here s my take on the problem  I m working on a project and I didn t want to go through the trouble of using Boost right now    std  string trim std  string str        if str length      0  return str       int beg   0  end   str length   - 1      while  str beg                    beg               while  str end                    end--             return str substr beg  end - beg   1       This solution will trim from the left and the right

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std  string trim  std  string  amp  amp  str         size t end   str find last not of     n r t         if   end    std  string  npos           str resize  end   1         size t start   str find first not of     n r t         if   start    std  string  npos           str   str substr  start         return std  move  str

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It is so annoying that I    have to google it  find out that I have to use rocket science  that there is no simple trim toupper function in string   For me this is the fastest way to solve it   CString tmp line c str     tmp   tmp Trim   MakeLower    string buffer   tmp    Ok  it is cool that I can use lambda ops  iterators  and all the stuff  But I only need to deal with a string instead of a character

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I have read most of the answers but did not found anyone making use of istringstream  std  string text    quot Let me split this into words quot    std  istringstream iss text   std  vector lt std  string gt  results  std  istream iterator lt std  string gt  iss                                     std  istream iterator lt std  string gt       The result is vector of words and it can deal with the strings having internal whitespace too  Hope this helped

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EDIT Since c  17  some parts of the standard library were removed  Fortunately  starting with c  11  we have lambdas which are a superior solution   include  lt algorithm gt    include  lt cctype gt   include  lt locale gt      trim from start  in place  static inline void ltrim std  string  amp s        s erase s begin    std  find if s begin    s end       unsigned char ch            return  std  isspace ch                  trim from end  in place  static inline void rtrim std  string  amp s        s erase std  find if s rbegin    s rend       unsigned char ch            return  std  isspace ch          base    s end           trim from both ends  in place  static inline void trim std  string  amp s        ltrim s       rtrim s         trim from start  copying  static inline std  string ltrim copy std  string s        ltrim s       return s        trim from end  copying  static inline std  string rtrim copy std  string s        rtrim s       return s        trim from both ends  copying  static inline std  string trim copy std  string s        trim s       return s     Thanks to https   stackoverflow com a 44973498 524503 for bringing up the modern solution  Original answer  I tend to use one of these 3 for my trimming needs   include  lt algorithm gt    include  lt functional gt    include  lt cctype gt   include  lt locale gt      trim from start static inline std  string  amp ltrim std  string  amp s        s erase s begin    std  find if s begin    s end                std  not1 std  ptr fun lt int  int gt  std  isspace          return s        trim from end static inline std  string  amp rtrim std  string  amp s        s erase std  find if s rbegin    s rend                std  not1 std  ptr fun lt int  int gt  std  isspace    base    s end         return s        trim from both ends static inline std  string  amp trim std  string  amp s        return ltrim rtrim s       They are fairly self-explanatory and work very well  EDIT  BTW  I have std  ptr fun in there to help disambiguate std  isspace because there is actually a second definition which supports locales  This could have been a cast just the same  but I tend to like this better  EDIT  To address some comments about accepting a parameter by reference  modifying and returning it  I Agree  An implementation that I would likely prefer would be two sets of functions  one for in place and one which makes a copy  A better set of examples would be   include  lt algorithm gt    include  lt functional gt    include  lt cctype gt   include  lt locale gt      trim from start  in place  static inline void ltrim std  string  amp s        s erase s begin    std  find if s begin    s end                std  not1 std  ptr fun lt int  int gt  std  isspace            trim from end  in place  static inline void rtrim std  string  amp s        s erase std  find if s rbegin    s rend                std  not1 std  ptr fun lt int  int gt  std  isspace    base    s end           trim from both ends  in place  static inline void trim std  string  amp s        ltrim s       rtrim s         trim from start  copying  static inline std  string ltrim copy std  string s        ltrim s       return s        trim from end  copying  static inline std  string rtrim copy std  string s        rtrim s       return s        trim from both ends  copying  static inline std  string trim copy std  string s        trim s       return s     I am keeping the original answer above though for context and in the interest of keeping the high voted answer still available

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The above methods are great  but sometimes you want to use a combination of functions for what your routine considers to be whitespace   In this case  using functors to combine operations can get messy so I prefer a simple loop I can modify for the trim   Here is a slightly modified trim function copied from the C version here on SO   In this example  I am trimming non alphanumeric characters   string trim char const  str         Trim leading non-letters   while  isalnum  str   str          Trim trailing non-letters   end   str   strlen str  - 1    while end  gt  str  amp  amp   isalnum  end   end--     return string str  end 1

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Yet another option - removes one or more characters from both ends   string strip const string amp  s  const string amp  chars            size t begin   0      size t end   s size  -1      for   begin  lt  s size    begin            if chars find first of s begin      string  npos              break      for   end  gt  begin  end--          if chars find first of s end      string  npos              break      return s substr begin  end-begin 1

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Poor man s string trim  spaces only   std  string trimSpaces const std  string amp  str        int start  len           for  start   0  start  lt  str size    amp  amp  str start          start         for  len   str size   - start  len  gt  0  amp  amp  str start   len - 1          len--            return str substr start  len

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For what it s worth  here is a trim implementation with an eye towards performance   It s much quicker than many other trim routines I ve seen around   Instead of using iterators and std  finds  it uses raw c strings and indices   It optimizes the following special cases  size 0 string  do nothing   string with no whitespace to trim  do nothing   string with only trailing whitespace to trim  just resize the string   string that s entirely whitespace  just clear the string    And finally  in the worst case  string with leading whitespace   it does its best to perform an efficient copy construction  performing only 1 copy and then moving that copy in place of the original string   void TrimString std  string  amp  str         if str empty            return       const auto pStr   str c str         size t front   0      while front  lt  str length    amp  amp  std  isspace int pStr front        front        size t back   str length        while back  gt  front  amp  amp  std  isspace int pStr back-1      --back        if 0    front                if back  lt  str length                          str resize back - front                       else if back  lt   front                str clear              else               str   std  move std  string str begin   front  str begin   back

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Hacked off of Cplusplus com  std  string choppa const std  string  amp t  const std  string  amp ws        std  string str   t      size t found      found   str find last not of ws       if  found    std  string  npos          str erase found 1       else         str clear                  str is all whitespace      return str      This works for the null case as well   -

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Using Boost s string algorithms would be easiest    include  lt boost algorithm string hpp gt   std  string str  hello world      boost  trim right str     str is now  hello world    There s also trim left and trim  which trims both sides     If you add  copy suffix to any of above function names e g  trim copy  the function will return a trimmed copy of the string instead of modifying it through a reference   If you add  if suffix to any of above function names e g  trim copy if  you can trim all characters satisfying your custom predicate  as opposed to just whitespaces

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Here s what I came up with    std  stringstream trimmer  trimmer  lt  lt  str  trimmer  gt  gt  str    Stream extraction eliminates whitespace automatically  so this works like a charm  Pretty clean and elegant too  if I do say so myself

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EDIT Since c  17  some parts of the standard library were removed  Fortunately  starting with c  11  we have lambdas which are a superior solution   include  lt algorithm gt    include  lt cctype gt   include  lt locale gt      trim from start  in place  static inline void ltrim std  string  amp s        s erase s begin    std  find if s begin    s end       unsigned char ch            return  std  isspace ch                  trim from end  in place  static inline void rtrim std  string  amp s        s erase std  find if s rbegin    s rend       unsigned char ch            return  std  isspace ch          base    s end           trim from both ends  in place  static inline void trim std  string  amp s        ltrim s       rtrim s         trim from start  copying  static inline std  string ltrim copy std  string s        ltrim s       return s        trim from end  copying  static inline std  string rtrim copy std  string s        rtrim s       return s        trim from both ends  copying  static inline std  string trim copy std  string s        trim s       return s     Thanks to https   stackoverflow com a 44973498 524503 for bringing up the modern solution  Original answer  I tend to use one of these 3 for my trimming needs   include  lt algorithm gt    include  lt functional gt    include  lt cctype gt   include  lt locale gt      trim from start static inline std  string  amp ltrim std  string  amp s        s erase s begin    std  find if s begin    s end                std  not1 std  ptr fun lt int  int gt  std  isspace          return s        trim from end static inline std  string  amp rtrim std  string  amp s        s erase std  find if s rbegin    s rend                std  not1 std  ptr fun lt int  int gt  std  isspace    base    s end         return s        trim from both ends static inline std  string  amp trim std  string  amp s        return ltrim rtrim s       They are fairly self-explanatory and work very well  EDIT  BTW  I have std  ptr fun in there to help disambiguate std  isspace because there is actually a second definition which supports locales  This could have been a cast just the same  but I tend to like this better  EDIT  To address some comments about accepting a parameter by reference  modifying and returning it  I Agree  An implementation that I would likely prefer would be two sets of functions  one for in place and one which makes a copy  A better set of examples would be   include  lt algorithm gt    include  lt functional gt    include  lt cctype gt   include  lt locale gt      trim from start  in place  static inline void ltrim std  string  amp s        s erase s begin    std  find if s begin    s end                std  not1 std  ptr fun lt int  int gt  std  isspace            trim from end  in place  static inline void rtrim std  string  amp s        s erase std  find if s rbegin    s rend                std  not1 std  ptr fun lt int  int gt  std  isspace    base    s end           trim from both ends  in place  static inline void trim std  string  amp s        ltrim s       rtrim s         trim from start  copying  static inline std  string ltrim copy std  string s        ltrim s       return s        trim from end  copying  static inline std  string rtrim copy std  string s        rtrim s       return s        trim from both ends  copying  static inline std  string trim copy std  string s        trim s       return s     I am keeping the original answer above though for context and in the interest of keeping the high voted answer still available

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I know this is a very old question  but I have added a few lines of code to yours and it trims whitespace from both ends   void trim std  string  amp line        auto val   line find last not of    n r t     1       if val    line size      val    std  string  npos           val   line find first not of    n r t            line   line substr val             else         line erase val

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My answer is an improvement upon the top answer for this post that trims control characters as well as spaces  0-32 and 127 on the ASCII table    std  isgraph determines if a character has a graphical representation  so you can use this to alter Evan s answer to remove any character that doesn t have a graphical representation from either side of a string   The result is a much more elegant solution    include  lt algorithm gt   include  lt functional gt   include  lt string gt           brief Left Trim       Trims whitespace from the left end of the provided std  string        param out  s The std  string to trim        return The modified std  string amp      std  string amp  ltrim std  string amp  s      s erase s begin    std  find if s begin    s end        std  ptr fun lt int  int gt  std  isgraph       return s             brief Right Trim       Trims whitespace from the right end of the provided std  string        param out  s The std  string to trim        return The modified std  string amp      std  string amp  rtrim std  string amp  s      s erase std  find if s rbegin    s rend        std  ptr fun lt int  int gt  std  isgraph   base    s end       return s             brief Trim       Trims whitespace from both ends of the provided std  string        param out  s The std  string to trim        return The modified std  string amp      std  string amp  trim std  string amp  s      return ltrim rtrim s        Note   Alternatively you should be able to use std  iswgraph if you need support for wide characters  but you will also have to edit this code to enable std  wstring manipulation  which is something that I haven t tested  see the reference page for std  basic string to explore this option

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Yet another option - removes one or more characters from both ends   string strip const string amp  s  const string amp  chars            size t begin   0      size t end   s size  -1      for   begin  lt  s size    begin            if chars find first of s begin      string  npos              break      for   end  gt  begin  end--          if chars find first of s end      string  npos              break      return s substr begin  end-begin 1

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Using Boost s string algorithms would be easiest    include  lt boost algorithm string hpp gt   std  string str  hello world      boost  trim right str     str is now  hello world    There s also trim left and trim  which trims both sides     If you add  copy suffix to any of above function names e g  trim copy  the function will return a trimmed copy of the string instead of modifying it through a reference   If you add  if suffix to any of above function names e g  trim copy if  you can trim all characters satisfying your custom predicate  as opposed to just whitespaces

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str erase 0  str find first not of  quot  t n v f r  quot        left trim str erase str find last not of  quot  t n v f r  quot     1      right trim

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Contributing my solution to the noise  trim defaults to creating a new string and returning the modified one while trim in place modifies the string passed to it  The trim function supports c  11 move semantics    include  lt string gt      modifies input string  returns input  std  string amp  trim left in place std  string amp  str        size t i   0      while i  lt  str size    amp  amp  isspace str i        i         return str erase 0  i      std  string amp  trim right in place std  string amp  str        size t i   str size        while i  gt  0  amp  amp  isspace str i - 1      --i         return str erase i  str size        std  string amp  trim in place std  string amp  str        return trim left in place trim right in place str          returns newly created strings  std  string trim right std  string str        return trim right in place str      std  string trim left std  string str        return trim left in place str      std  string trim std  string str        return trim left in place trim right in place str        include  lt cassert gt   int main          std  string s1    t r n          std  string s2     r nc        std  string s3  c  t        std  string s4     rc          assert trim s1              assert trim s2      c        assert trim s3      c        assert trim s4      c         assert s1       t r n          assert s2        r nc        assert s3     c  t        assert s4        rc          assert trim in place s1              assert trim in place s2      c        assert trim in place s3      c        assert trim in place s4      c         assert s1             assert s2     c        assert s3     c        assert s4     c

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I m using this one   void trim string  amp str       int i 0         left trim     while  isspace str i    0          i        str   str substr i str length  -i          right trim     i str length  -1      while  isspace str i    0          i--      str   str substr 0 i 1

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Hacked off of Cplusplus com  std  string choppa const std  string  amp t  const std  string  amp ws        std  string str   t      size t found      found   str find last not of ws       if  found    std  string  npos          str erase found 1       else         str clear                  str is all whitespace      return str      This works for the null case as well   -

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Bit late to the party  but never mind  Now C  11 is here  we have lambdas and auto variables  So my version  which also handles all-whitespace and empty strings  is    include  lt cctype gt   include  lt string gt   include  lt algorithm gt   inline std  string trim const std  string  amp s       auto wsfront std  find if not s begin   s end      int c  return std  isspace c         auto wsback std  find if not s rbegin   s rend      int c  return std  isspace c     base       return  wsback lt  wsfront   std  string     std  string wsfront wsback        We could make a reverse iterator from wsfront and use that as the termination condition in the second find if not but that s only useful in the case of an all-whitespace string  and gcc 4 8 at least isn t smart enough to infer the type of the reverse iterator  std  string  const reverse iterator  with auto  I don t know how expensive constructing a reverse iterator is  so YMMV here  With this alteration  the code looks like this   inline std  string trim const std  string  amp s       auto  wsfront std  find if not s begin   s end      int c  return std  isspace c         return std  string wsfront std  find if not s rbegin   std  string  const reverse iterator wsfront     int c  return std  isspace c     base

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In the case of an empty string  your code assumes that adding 1 to string  npos gives 0  string  npos is of type string  size type  which is unsigned  Thus  you are relying on the overflow behaviour of addition

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As I wanted to update my old C   trim function with a C   11 approach I have tested a lot of the posted answers to the question  My conclusion is that I keep my old C   solution    It is the fastest one by large  even adding more characters to check  e g   r n I see no use case for  f v  is still faster than the solutions using algorithm   std  string  amp  trimMe  std  string  amp  str          right trim    while  str length     gt  0  amp  amp   str  str length   -1            str  str length   -1       t          str erase  str length   -1  1          left trim    while  str length     gt  0  amp  amp   str  0            str  0       t          str erase  0  1      return str

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For what it s worth  here is a trim implementation with an eye towards performance   It s much quicker than many other trim routines I ve seen around   Instead of using iterators and std  finds  it uses raw c strings and indices   It optimizes the following special cases  size 0 string  do nothing   string with no whitespace to trim  do nothing   string with only trailing whitespace to trim  just resize the string   string that s entirely whitespace  just clear the string    And finally  in the worst case  string with leading whitespace   it does its best to perform an efficient copy construction  performing only 1 copy and then moving that copy in place of the original string   void TrimString std  string  amp  str         if str empty            return       const auto pStr   str c str         size t front   0      while front  lt  str length    amp  amp  std  isspace int pStr front        front        size t back   str length        while back  gt  front  amp  amp  std  isspace int pStr back-1      --back        if 0    front                if back  lt  str length                          str resize back - front                       else if back  lt   front                str clear              else               str   std  move std  string str begin   front  str begin   back

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Ok this maight not be the fastest but it s    simple   str       aaa       int len   str length       rtrim while str len-1            str erase --len 1        ltrim while str 0            str erase 0 1

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This any good    Cause this post totally needs another answer     string trimBegin string str        string whites     t r n        int i   0      while  whites find str i        whites  npos       str erase 0  i       return str      Similar case for the trimEnd  just reverse the polari- er  indices

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c  11   int i    string s     h e ll  t n  o   string trim      n t    while   i   s find first of trim      -1      s erase i 1    cout  lt  lt  s    output   hello   works fine also with empty strings

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It is so annoying that I    have to google it  find out that I have to use rocket science  that there is no simple trim toupper function in string   For me this is the fastest way to solve it   CString tmp line c str     tmp   tmp Trim   MakeLower    string buffer   tmp    Ok  it is cool that I can use lambda ops  iterators  and all the stuff  But I only need to deal with a string instead of a character

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Here is a solution for trim with regex   include  lt string gt   include  lt regex gt   string trim string str       return regex replace str  regex

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This is what I use   Just keep removing space from the front  and then  if there s anything left  do the same from the back   void trim string amp  s        while s compare 0 1       0          s erase s begin        remove leading whitespaces     while s size   gt 0  amp  amp  s compare s size  -1 1       0          s erase s end  -1      remove trailing whitespaces

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What about this       include  lt iostream gt   include  lt string gt   include  lt regex gt   std  string ltrim  std  string str         return std  regex replace  str  std  regex     s     std  string           std  string rtrim  std  string str         return std  regex replace  str  std  regex    s      std  string           std  string trim  std  string str         return ltrim  rtrim  str         int main          std  string str        t  this is a test string   n          std  cout  lt  lt   -   lt  lt  trim  str    lt  lt   - n       return 0       Note  I m still relatively new to C    so please forgive me if I m off base here

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This version trims internal whitespace and non-alphanumerics   static inline std  string  amp trimAll std  string  amp s           if s size      0                return s             int val   0      for  int cur   0  cur  lt  s size    cur                  if s cur          amp  amp  std  isalnum s cur                          s val    s cur               val                        s resize val       return s

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Ok this maight not be the fastest but it s    simple   str       aaa       int len   str length       rtrim while str len-1            str erase --len 1        ltrim while str 0            str erase 0 1

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I like tzaman s solution  the only problem with it is that it doesn t trim a string containing only spaces   To correct that 1 flaw  add a str clear   in between the 2 trimmer lines  std  stringstream trimmer  trimmer  lt  lt  str  str clear    trimmer  gt  gt  str

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I m not sure if your environment is the same  but in mine  the empty string case will cause the program to abort  I would either wrap that erase call with an if  s empty    or use Boost as already mentioned

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What about this       include  lt iostream gt   include  lt string gt   include  lt regex gt   std  string ltrim  std  string str         return std  regex replace  str  std  regex     s     std  string           std  string rtrim  std  string str         return std  regex replace  str  std  regex    s      std  string           std  string trim  std  string str         return ltrim  rtrim  str         int main          std  string str        t  this is a test string   n          std  cout  lt  lt   -   lt  lt  trim  str    lt  lt   - n       return 0       Note  I m still relatively new to C    so please forgive me if I m off base here

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Trims both ends  string trim const std  string  amp str       string result    quot  quot       size t endIndex   str size        while  endIndex  gt  0  amp  amp  isblank str endIndex-1            endIndex -  1      for  size t i 0  i lt endIndex   i  1           char ch   str i           if   isblank ch     result size   gt 0              result    ch           return result

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I m not sure if your environment is the same  but in mine  the empty string case will cause the program to abort  I would either wrap that erase call with an if  s empty    or use Boost as already mentioned

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With C  11 also came a regular expression module  which of course can be used to trim leading or trailing spaces   Maybe something like this   std  string ltrim const std  string amp  s        static const std  regex lws      space       std  regex constants  extended       return std  regex replace s  lws          std  string rtrim const std  string amp  s        static const std  regex tws     space        std  regex constants  extended       return std  regex replace s  tws          std  string trim const std  string amp  s        return ltrim rtrim s

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why not use lambda  auto no space      char ch  - gt  bool     return  std  isspace lt char gt  ch  std  locale  classic        auto ltrim      std  string amp  s  - gt  std  string amp      s erase s begin    std  find if s begin    s end    no space      return s     auto rtrim      std  string amp  s  - gt  std  string amp      s erase std  find if s rbegin    s rend    no space  base    s end       return s     auto trim copy      std  string s  - gt  std  string amp    return ltrim rtrim s       auto trim      std  string amp  s  - gt  std  string amp    return ltrim rtrim s

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Here is a straight forward implementation   For such a simple operation  you probably should not be using any special constructs   The build-in isspace   function takes care of various forms of white characters  so we should take advantage of it   You also have to consider special cases where the string is empty or simply a bunch of spaces  Trim left or right could be derived from the following code   string trimSpace const string  amp str       if  str empty    return str     string  size type i j     i 0     while  i lt str size    amp  amp  isspace str i      i     if  i    str size          return string       empty string    j   str size   - 1       while  j gt 0  amp  amp  isspace str j    --j     the j gt 0 check is not needed    while  isspace str j    --j    return str substr i  j-i 1

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In the case of an empty string  your code assumes that adding 1 to string  npos gives 0  string  npos is of type string  size type  which is unsigned  Thus  you are relying on the overflow behaviour of addition

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Here is a straight forward implementation   For such a simple operation  you probably should not be using any special constructs   The build-in isspace   function takes care of various forms of white characters  so we should take advantage of it   You also have to consider special cases where the string is empty or simply a bunch of spaces  Trim left or right could be derived from the following code   string trimSpace const string  amp str       if  str empty    return str     string  size type i j     i 0     while  i lt str size    amp  amp  isspace str i      i     if  i    str size          return string       empty string    j   str size   - 1       while  j gt 0  amp  amp  isspace str j    --j     the j gt 0 check is not needed    while  isspace str j    --j    return str substr i  j-i 1

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I m not sure if your environment is the same  but in mine  the empty string case will cause the program to abort  I would either wrap that erase call with an if  s empty    or use Boost as already mentioned

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EDIT Since c  17  some parts of the standard library were removed  Fortunately  starting with c  11  we have lambdas which are a superior solution   include  lt algorithm gt    include  lt cctype gt   include  lt locale gt      trim from start  in place  static inline void ltrim std  string  amp s        s erase s begin    std  find if s begin    s end       unsigned char ch            return  std  isspace ch                  trim from end  in place  static inline void rtrim std  string  amp s        s erase std  find if s rbegin    s rend       unsigned char ch            return  std  isspace ch          base    s end           trim from both ends  in place  static inline void trim std  string  amp s        ltrim s       rtrim s         trim from start  copying  static inline std  string ltrim copy std  string s        ltrim s       return s        trim from end  copying  static inline std  string rtrim copy std  string s        rtrim s       return s        trim from both ends  copying  static inline std  string trim copy std  string s        trim s       return s     Thanks to https   stackoverflow com a 44973498 524503 for bringing up the modern solution  Original answer  I tend to use one of these 3 for my trimming needs   include  lt algorithm gt    include  lt functional gt    include  lt cctype gt   include  lt locale gt      trim from start static inline std  string  amp ltrim std  string  amp s        s erase s begin    std  find if s begin    s end                std  not1 std  ptr fun lt int  int gt  std  isspace          return s        trim from end static inline std  string  amp rtrim std  string  amp s        s erase std  find if s rbegin    s rend                std  not1 std  ptr fun lt int  int gt  std  isspace    base    s end         return s        trim from both ends static inline std  string  amp trim std  string  amp s        return ltrim rtrim s       They are fairly self-explanatory and work very well  EDIT  BTW  I have std  ptr fun in there to help disambiguate std  isspace because there is actually a second definition which supports locales  This could have been a cast just the same  but I tend to like this better  EDIT  To address some comments about accepting a parameter by reference  modifying and returning it  I Agree  An implementation that I would likely prefer would be two sets of functions  one for in place and one which makes a copy  A better set of examples would be   include  lt algorithm gt    include  lt functional gt    include  lt cctype gt   include  lt locale gt      trim from start  in place  static inline void ltrim std  string  amp s        s erase s begin    std  find if s begin    s end                std  not1 std  ptr fun lt int  int gt  std  isspace            trim from end  in place  static inline void rtrim std  string  amp s        s erase std  find if s rbegin    s rend                std  not1 std  ptr fun lt int  int gt  std  isspace    base    s end           trim from both ends  in place  static inline void trim std  string  amp s        ltrim s       rtrim s         trim from start  copying  static inline std  string ltrim copy std  string s        ltrim s       return s        trim from end  copying  static inline std  string rtrim copy std  string s        rtrim s       return s        trim from both ends  copying  static inline std  string trim copy std  string s        trim s       return s     I am keeping the original answer above though for context and in the interest of keeping the high voted answer still available

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Contributing my solution to the noise  trim defaults to creating a new string and returning the modified one while trim in place modifies the string passed to it  The trim function supports c  11 move semantics    include  lt string gt      modifies input string  returns input  std  string amp  trim left in place std  string amp  str        size t i   0      while i  lt  str size    amp  amp  isspace str i        i         return str erase 0  i      std  string amp  trim right in place std  string amp  str        size t i   str size        while i  gt  0  amp  amp  isspace str i - 1      --i         return str erase i  str size        std  string amp  trim in place std  string amp  str        return trim left in place trim right in place str          returns newly created strings  std  string trim right std  string str        return trim right in place str      std  string trim left std  string str        return trim left in place str      std  string trim std  string str        return trim left in place trim right in place str        include  lt cassert gt   int main          std  string s1    t r n          std  string s2     r nc        std  string s3  c  t        std  string s4     rc          assert trim s1              assert trim s2      c        assert trim s3      c        assert trim s4      c         assert s1       t r n          assert s2        r nc        assert s3     c  t        assert s4        rc          assert trim in place s1              assert trim in place s2      c        assert trim in place s3      c        assert trim in place s4      c         assert s1             assert s2     c        assert s3     c        assert s4     c

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I know this is a very old question  but I have added a few lines of code to yours and it trims whitespace from both ends   void trim std  string  amp line        auto val   line find last not of    n r t     1       if val    line size      val    std  string  npos           val   line find first not of    n r t            line   line substr val             else         line erase val

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An elegant way of doing it can be like  std  string  amp  trim std  string  amp  str       return ltrim rtrim str        And the supportive functions are implemented as   std  string  amp  ltrim std  string  amp  str      auto it    std  find if  str begin     str end        char ch   return  std  isspace lt char gt  ch   std  locale  classic              str erase  str begin     it     return str        std  string  amp  rtrim std  string  amp  str      auto it    std  find if  str rbegin     str rend        char ch   return  std  isspace lt char gt  ch   std  locale  classic              str erase  it base     str end        return str         And once you ve all these in place  you can write this as well   std  string trim copy std  string const  amp  str       auto s   str     return ltrim rtrim s

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Use the following code to right trim  trailing  spaces and tab characters from std  strings  ideone       trim trailing spaces size t endpos   str find last not of    t    size t startpos   str find first not of    t    if  std  string  npos    endpos         str   str substr  0  endpos 1        str   str substr  startpos      else       str erase std  remove std  begin str   std  end str         std  end str        And just to balance things out  I ll include the left trim code too  ideone       trim leading spaces size t startpos   str find first not of    t    if  string  npos    startpos         str   str substr  startpos

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This can be done more simply in C  11 due to the addition of back   and pop back     while    s empty    amp  amp  isspace s back      s pop back

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Hacked off of Cplusplus com  std  string choppa const std  string  amp t  const std  string  amp ws        std  string str   t      size t found      found   str find last not of ws       if  found    std  string  npos          str erase found 1       else         str clear                  str is all whitespace      return str      This works for the null case as well   -

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EDIT Since c  17  some parts of the standard library were removed  Fortunately  starting with c  11  we have lambdas which are a superior solution   include  lt algorithm gt    include  lt cctype gt   include  lt locale gt      trim from start  in place  static inline void ltrim std  string  amp s        s erase s begin    std  find if s begin    s end       unsigned char ch            return  std  isspace ch                  trim from end  in place  static inline void rtrim std  string  amp s        s erase std  find if s rbegin    s rend       unsigned char ch            return  std  isspace ch          base    s end           trim from both ends  in place  static inline void trim std  string  amp s        ltrim s       rtrim s         trim from start  copying  static inline std  string ltrim copy std  string s        ltrim s       return s        trim from end  copying  static inline std  string rtrim copy std  string s        rtrim s       return s        trim from both ends  copying  static inline std  string trim copy std  string s        trim s       return s     Thanks to https   stackoverflow com a 44973498 524503 for bringing up the modern solution  Original answer  I tend to use one of these 3 for my trimming needs   include  lt algorithm gt    include  lt functional gt    include  lt cctype gt   include  lt locale gt      trim from start static inline std  string  amp ltrim std  string  amp s        s erase s begin    std  find if s begin    s end                std  not1 std  ptr fun lt int  int gt  std  isspace          return s        trim from end static inline std  string  amp rtrim std  string  amp s        s erase std  find if s rbegin    s rend                std  not1 std  ptr fun lt int  int gt  std  isspace    base    s end         return s        trim from both ends static inline std  string  amp trim std  string  amp s        return ltrim rtrim s       They are fairly self-explanatory and work very well  EDIT  BTW  I have std  ptr fun in there to help disambiguate std  isspace because there is actually a second definition which supports locales  This could have been a cast just the same  but I tend to like this better  EDIT  To address some comments about accepting a parameter by reference  modifying and returning it  I Agree  An implementation that I would likely prefer would be two sets of functions  one for in place and one which makes a copy  A better set of examples would be   include  lt algorithm gt    include  lt functional gt    include  lt cctype gt   include  lt locale gt      trim from start  in place  static inline void ltrim std  string  amp s        s erase s begin    std  find if s begin    s end                std  not1 std  ptr fun lt int  int gt  std  isspace            trim from end  in place  static inline void rtrim std  string  amp s        s erase std  find if s rbegin    s rend                std  not1 std  ptr fun lt int  int gt  std  isspace    base    s end           trim from both ends  in place  static inline void trim std  string  amp s        ltrim s       rtrim s         trim from start  copying  static inline std  string ltrim copy std  string s        ltrim s       return s        trim from end  copying  static inline std  string rtrim copy std  string s        rtrim s       return s        trim from both ends  copying  static inline std  string trim copy std  string s        trim s       return s     I am keeping the original answer above though for context and in the interest of keeping the high voted answer still available

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With C  17 you can use basic string view  remove prefix and basic string view  remove suffix   std  string view trim std  string view s        s remove prefix std  min s find first not of    t r v n    s size          s remove suffix std  min s size   - s find last not of    t r v n   - 1  s size           return s      A nice alternative   std  string view ltrim std  string view s        s remove prefix std  distance s cbegin    std  find if s cbegin    s cend                int c   return  std  isspace c             return s     std  string view rtrim std  string view s        s remove suffix std  distance s crbegin    std  find if s crbegin    s crend               int c   return  std  isspace c             return s     std  string view trim std  string view s        return ltrim rtrim s

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I like tzaman s solution  the only problem with it is that it doesn t trim a string containing only spaces   To correct that 1 flaw  add a str clear   in between the 2 trimmer lines  std  stringstream trimmer  trimmer  lt  lt  str  str clear    trimmer  gt  gt  str

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Below is one pass may be two pass  solution  It goes over the white spaces part of string twice and non-whitespace part once   void trim std  string amp  s                                                                                                                                                                                                                       if  s empty                                                                                                                                                                                                                                    return                                                                                                                                                                                                                                  int l   0  r   s size    - 1                                                                                                                                                                                                                while  l  lt  s size    amp  amp  std  isspace s l          l points to first non-whitespace char                                                                                                                                                     while  r  gt   0  amp  amp  std  isspace s r--        r points to last non-whitespace char                                                                                                                                                             if  l  gt  r                                                                                                                                                                                                                                      s                                                                                                                                                                                                                                      else                                                                                                                                                                                                                                           l--                                                                                                                                                                                                                                        r                                                                                                                                                                                                                                          int wi   0                                                                                                                                                                                                                                 while  l  lt   r                                                                                                                                                                                                                                  s wi      s l                                                                                                                                                                                                                          s erase wi                                                                                                                                                                                                                                                                                                                                                                                                                                                                        return

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The above methods are great  but sometimes you want to use a combination of functions for what your routine considers to be whitespace   In this case  using functors to combine operations can get messy so I prefer a simple loop I can modify for the trim   Here is a slightly modified trim function copied from the C version here on SO   In this example  I am trimming non alphanumeric characters   string trim char const  str         Trim leading non-letters   while  isalnum  str   str          Trim trailing non-letters   end   str   strlen str  - 1    while end  gt  str  amp  amp   isalnum  end   end--     return string str  end 1

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This is what I use   Just keep removing space from the front  and then  if there s anything left  do the same from the back   void trim string amp  s        while s compare 0 1       0          s erase s begin        remove leading whitespaces     while s size   gt 0  amp  amp  s compare s size  -1 1       0          s erase s end  -1      remove trailing whitespaces

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Below is one pass may be two pass  solution  It goes over the white spaces part of string twice and non-whitespace part once   void trim std  string amp  s                                                                                                                                                                                                                       if  s empty                                                                                                                                                                                                                                    return                                                                                                                                                                                                                                  int l   0  r   s size    - 1                                                                                                                                                                                                                while  l  lt  s size    amp  amp  std  isspace s l          l points to first non-whitespace char                                                                                                                                                     while  r  gt   0  amp  amp  std  isspace s r--        r points to last non-whitespace char                                                                                                                                                             if  l  gt  r                                                                                                                                                                                                                                      s                                                                                                                                                                                                                                      else                                                                                                                                                                                                                                           l--                                                                                                                                                                                                                                        r                                                                                                                                                                                                                                          int wi   0                                                                                                                                                                                                                                 while  l  lt   r                                                                                                                                                                                                                                  s wi      s l                                                                                                                                                                                                                          s erase wi                                                                                                                                                                                                                                                                                                                                                                                                                                                                        return

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std  string trim  std  string  amp  amp  str         size t end   str find last not of     n r t         if   end    std  string  npos           str resize  end   1         size t start   str find first not of     n r t         if   start    std  string  npos           str   str substr  start         return std  move  str

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My solution based on the answer by  Bill the Lizard   Note that these functions will return the empty string if the input string contains nothing but whitespace   const std  string StringUtils  WHITESPACE      n r t    std  string StringUtils  Trim const std  string amp  s        return TrimRight TrimLeft s       std  string StringUtils  TrimLeft const std  string amp  s        size t startpos   s find first not of StringUtils  WHITESPACE       return  startpos    std  string  npos         s substr startpos      std  string StringUtils  TrimRight const std  string amp  s        size t endpos   s find last not of StringUtils  WHITESPACE       return  endpos    std  string  npos         s substr 0  endpos 1

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Try this  it works for me   inline std  string trim std  string amp  str        str erase 0  str find first not of                prefixing spaces     str erase str find last not of      1             surfixing spaces     return str

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An elegant way of doing it can be like  std  string  amp  trim std  string  amp  str       return ltrim rtrim str        And the supportive functions are implemented as   std  string  amp  ltrim std  string  amp  str      auto it    std  find if  str begin     str end        char ch   return  std  isspace lt char gt  ch   std  locale  classic              str erase  str begin     it     return str        std  string  amp  rtrim std  string  amp  str      auto it    std  find if  str rbegin     str rend        char ch   return  std  isspace lt char gt  ch   std  locale  classic              str erase  it base     str end        return str         And once you ve all these in place  you can write this as well   std  string trim copy std  string const  amp  str       auto s   str     return ltrim rtrim s

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I m using this one   void trim string  amp str       int i 0         left trim     while  isspace str i    0          i        str   str substr i str length  -i          right trim     i str length  -1      while  isspace str i    0          i--      str   str substr 0 i 1

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What you are doing is fine and robust  I have used the same method for a long time and I have yet to find a faster method   const char  ws      t n r f v       trim from end of string  right  inline std  string amp  rtrim std  string amp  s  const char  t   ws        s erase s find last not of t    1       return s        trim from beginning of string  left  inline std  string amp  ltrim std  string amp  s  const char  t   ws        s erase 0  s find first not of t        return s        trim from both ends of string  right then left  inline std  string amp  trim std  string amp  s  const char  t   ws        return ltrim rtrim s  t   t       By supplying the characters to be trimmed you have the flexibility to trim non-whitespace characters and the efficiency to trim only the characters you want trimmed

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Bit late to the party  but never mind  Now C  11 is here  we have lambdas and auto variables  So my version  which also handles all-whitespace and empty strings  is    include  lt cctype gt   include  lt string gt   include  lt algorithm gt   inline std  string trim const std  string  amp s       auto wsfront std  find if not s begin   s end      int c  return std  isspace c         auto wsback std  find if not s rbegin   s rend      int c  return std  isspace c     base       return  wsback lt  wsfront   std  string     std  string wsfront wsback        We could make a reverse iterator from wsfront and use that as the termination condition in the second find if not but that s only useful in the case of an all-whitespace string  and gcc 4 8 at least isn t smart enough to infer the type of the reverse iterator  std  string  const reverse iterator  with auto  I don t know how expensive constructing a reverse iterator is  so YMMV here  With this alteration  the code looks like this   inline std  string trim const std  string  amp s       auto  wsfront std  find if not s begin   s end      int c  return std  isspace c         return std  string wsfront std  find if not s rbegin   std  string  const reverse iterator wsfront     int c  return std  isspace c     base

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s erase 0  s find first not of    n r t                                                                                                    s erase s find last not of    n r t   1

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Using Boost s string algorithms would be easiest    include  lt boost algorithm string hpp gt   std  string str  hello world      boost  trim right str     str is now  hello world    There s also trim left and trim  which trims both sides     If you add  copy suffix to any of above function names e g  trim copy  the function will return a trimmed copy of the string instead of modifying it through a reference   If you add  if suffix to any of above function names e g  trim copy if  you can trim all characters satisfying your custom predicate  as opposed to just whitespaces

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The accepted answer and even Boost s version did not work for me  so I wrote the following version   std  string trim const std  string amp  input        std  stringstream string stream      for  const auto character   input            if   isspace character                 string stream  lt  lt  character                       return string stream str        This will remove any whitespace character from anywhere in the string and return a new copy of the string

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The accepted answer and even Boost s version did not work for me  so I wrote the following version   std  string trim const std  string amp  input        std  stringstream string stream      for  const auto character   input            if   isspace character                 string stream  lt  lt  character                       return string stream str        This will remove any whitespace character from anywhere in the string and return a new copy of the string

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This version trims internal whitespace and non-alphanumerics   static inline std  string  amp trimAll std  string  amp s           if s size      0                return s             int val   0      for  int cur   0  cur  lt  s size    cur                  if s cur          amp  amp  std  isalnum s cur                          s val    s cur               val                        s resize val       return s

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s erase 0  s find first not of    n r t                                                                                                    s erase s find last not of    n r t   1

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I m not sure if your environment is the same  but in mine  the empty string case will cause the program to abort  I would either wrap that erase call with an if  s empty    or use Boost as already mentioned

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Here is a solution for trim with regex   include  lt string gt   include  lt regex gt   string trim string str       return regex replace str  regex

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Here is my version   size t beg   s find first not of    r n    return  beg    string  npos         in substr beg  s find last not of    r n   - beg

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What you are doing is fine and robust  I have used the same method for a long time and I have yet to find a faster method   const char  ws      t n r f v       trim from end of string  right  inline std  string amp  rtrim std  string amp  s  const char  t   ws        s erase s find last not of t    1       return s        trim from beginning of string  left  inline std  string amp  ltrim std  string amp  s  const char  t   ws        s erase 0  s find first not of t        return s        trim from both ends of string  right then left  inline std  string amp  trim std  string amp  s  const char  t   ws        return ltrim rtrim s  t   t       By supplying the characters to be trimmed you have the flexibility to trim non-whitespace characters and the efficiency to trim only the characters you want trimmed

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Here s a solution easy to understand for beginners not used to write std   everywhere and not yet familiar with const-correctness  iterators  STL algorithms  etc      include  lt string gt   include  lt cctype gt     for isspace using namespace std       Left trim the given string     hello     -- gt   hello      string left trim string str        int numStartSpaces   0      for  int i   0  i  lt  str length    i              if   isspace str i    break          numStartSpaces              return str substr numStartSpaces         Right trim the given string     hello     -- gt     hello    string right trim string str        int numEndSpaces   0      for  int i   str length   - 1  i  gt   0  i--            if   isspace str i    break          numEndSpaces              return str substr 0  str length   - numEndSpaces         Left and right trim the given string     hello     -- gt   hello    string trim string str        return right trim left trim str        Hope it helps

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str erase 0  str find first not of  quot  t n v f r  quot        left trim str erase str find last not of  quot  t n v f r  quot     1      right trim

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Trim C  11 implementation   static void trim std  string  amp s         s erase s begin    std  find if not s begin    s end       char c   return std  isspace c             s erase std  find if not s rbegin    s rend       char c   return std  isspace c      base    s end

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In the case of an empty string  your code assumes that adding 1 to string  npos gives 0  string  npos is of type string  size type  which is unsigned  Thus  you are relying on the overflow behaviour of addition

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With C  17 you can use basic string view  remove prefix and basic string view  remove suffix   std  string view trim std  string view s        s remove prefix std  min s find first not of    t r v n    s size          s remove suffix std  min s size   - s find last not of    t r v n   - 1  s size           return s      A nice alternative   std  string view ltrim std  string view s        s remove prefix std  distance s cbegin    std  find if s cbegin    s cend                int c   return  std  isspace c             return s     std  string view rtrim std  string view s        s remove suffix std  distance s crbegin    std  find if s crbegin    s crend               int c   return  std  isspace c             return s     std  string view trim std  string view s        return ltrim rtrim s

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http   ideone com nFVtEo  std  string trim const std  string  amp s        std  string  const iterator it   s begin        while  it    s end    amp  amp  isspace  it           it         std  string  const reverse iterator rit   s rbegin        while  rit base      it  amp  amp  isspace  rit           rit         return std  string it  rit base

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It seems I m really late to the party - I can t believe this was asked 7 years ago    Here s my take on the problem  I m working on a project and I didn t want to go through the trouble of using Boost right now    std  string trim std  string str        if str length      0  return str       int beg   0  end   str length   - 1      while  str beg                    beg               while  str end                    end--             return str substr beg  end - beg   1       This solution will trim from the left and the right

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My answer is an improvement upon the top answer for this post that trims control characters as well as spaces  0-32 and 127 on the ASCII table    std  isgraph determines if a character has a graphical representation  so you can use this to alter Evan s answer to remove any character that doesn t have a graphical representation from either side of a string   The result is a much more elegant solution    include  lt algorithm gt   include  lt functional gt   include  lt string gt           brief Left Trim       Trims whitespace from the left end of the provided std  string        param out  s The std  string to trim        return The modified std  string amp      std  string amp  ltrim std  string amp  s      s erase s begin    std  find if s begin    s end        std  ptr fun lt int  int gt  std  isgraph       return s             brief Right Trim       Trims whitespace from the right end of the provided std  string        param out  s The std  string to trim        return The modified std  string amp      std  string amp  rtrim std  string amp  s      s erase std  find if s rbegin    s rend        std  ptr fun lt int  int gt  std  isgraph   base    s end       return s             brief Trim       Trims whitespace from both ends of the provided std  string        param out  s The std  string to trim        return The modified std  string amp      std  string amp  trim std  string amp  s      return ltrim rtrim s        Note   Alternatively you should be able to use std  iswgraph if you need support for wide characters  but you will also have to edit this code to enable std  wstring manipulation  which is something that I haven t tested  see the reference page for std  basic string to explore this option

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Here s what I came up with    std  stringstream trimmer  trimmer  lt  lt  str  trimmer  gt  gt  str    Stream extraction eliminates whitespace automatically  so this works like a charm  Pretty clean and elegant too  if I do say so myself

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In the case of an empty string  your code assumes that adding 1 to string  npos gives 0  string  npos is of type string  size type  which is unsigned  Thus  you are relying on the overflow behaviour of addition

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http   ideone com nFVtEo  std  string trim const std  string  amp s        std  string  const iterator it   s begin        while  it    s end    amp  amp  isspace  it           it         std  string  const reverse iterator rit   s rbegin        while  rit base      it  amp  amp  isspace  rit           rit         return std  string it  rit base

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why not use lambda  auto no space      char ch  - gt  bool     return  std  isspace lt char gt  ch  std  locale  classic        auto ltrim      std  string amp  s  - gt  std  string amp      s erase s begin    std  find if s begin    s end    no space      return s     auto rtrim      std  string amp  s  - gt  std  string amp      s erase std  find if s rbegin    s rend    no space  base    s end       return s     auto trim copy      std  string s  - gt  std  string amp    return ltrim rtrim s       auto trim      std  string amp  s  - gt  std  string amp    return ltrim rtrim s

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My solution based on the answer by  Bill the Lizard   Note that these functions will return the empty string if the input string contains nothing but whitespace   const std  string StringUtils  WHITESPACE      n r t    std  string StringUtils  Trim const std  string amp  s        return TrimRight TrimLeft s       std  string StringUtils  TrimLeft const std  string amp  s        size t startpos   s find first not of StringUtils  WHITESPACE       return  startpos    std  string  npos         s substr startpos      std  string StringUtils  TrimRight const std  string amp  s        size t endpos   s find last not of StringUtils  WHITESPACE       return  endpos    std  string  npos         s substr 0  endpos 1

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c  11   int i    string s     h e ll  t n  o   string trim      n t    while   i   s find first of trim      -1      s erase i 1    cout  lt  lt  s    output   hello   works fine also with empty strings

[c++] What's the best way to trim std::string?

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