Trim whitespace from a String

Question

I know there are several ways to do this in Java and C that are nice  but in C   I can t seem to find a way to easily implement a string trimming function   This is what I currently have   string trim string amp  str        size t first   str find first not of           size t last   str find last not of           return str substr first   last-first 1        but whenever I try and call   trim myString     I get the compiler error    tmp ccZZKSEq o  In function  song  Read std  basic ifstream lt char   std  char traits lt char gt   gt  amp   std  basic ifstream lt char  std  char traits lt char gt   gt  amp   char const   char const     song cpp   text 0x31c   undefined reference to  song  trim std  string amp    collect2  error  ld returned 1 exit status   I am trying to find a simple and standard way of trimming leading and trailing whitespace from a string without it taking up 100 lines of code  and I tried using regex  but could not get that to work as well   I also cannot use Boost

User · Answer

include  lt vector gt   include  lt numeric gt   include  lt sstream gt   include  lt iterator gt   void Trim std  string amp  inputString        std  istringstream stringStream inputString       std  vector lt std  string gt  tokens  std  istream iterator lt std  string gt  stringStream    std  istream iterator lt std  string gt           inputString   std  accumulate std  next tokens begin     tokens end                                     tokens 0      start with first element                                     std  string a  std  string b    return a         b

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In addition to answer of  gjha   inline std  string ltrim copy const std  string amp  str        auto it   std  find if str cbegin    str cend               char ch    return  std  isspace lt char gt  ch  std  locale  classic             return std  string it  str cend        inline std  string rtrim copy const std  string amp  str        auto it   std  find if str crbegin    str crend               char ch    return  std  isspace lt char gt  ch  std  locale  classic             return it    str crend     std  string     std  string str cbegin      it base        inline std  string trim copy const std  string amp  str        auto it1   std  find if str cbegin    str cend               char ch    return  std  isspace lt char gt  ch  std  locale  classic             if  it1    str cend              return std  string              auto it2   std  find if str crbegin    str crend               char ch    return  std  isspace lt char gt  ch  std  locale  classic             return it2    str crend     std  string it1  str cend      std  string it1    it2 base

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Using a regex  include  lt regex gt   include  lt string gt   string trim string s        regex e  quot    s    s   quot         remove leading and trailing spaces     return regex replace s  e   quot  quot       Credit to  https   www regular-expressions info examples html for the regex

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Your code is fine  What you are seeing is a linker issue   If you put your code in a single file like this    include  lt iostream gt   include  lt string gt   using namespace std   string trim const string amp  str        size t first   str find first not of           if  string  npos    first                return str            size t last   str find last not of           return str substr first   last - first   1       int main         string s    abc        cout  lt  lt  trim s        then do g   test cc and run a out  you will see it works   You should check if the file that contains the trim function is included in the link stage of your compilation process

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Here is how you can do it   std  string  amp  trim std  string  amp  str       return ltrim rtrim str        And the supportive functions are implemeted as   std  string  amp  ltrim std  string  amp  str      auto it2    std  find if  str begin     str end        char ch   return  std  isspace lt char gt  ch   std  locale  classic              str erase  str begin     it2     return str        std  string  amp  rtrim std  string  amp  str      auto it1    std  find if  str rbegin     str rend        char ch   return  std  isspace lt char gt  ch   std  locale  classic              str erase  it1 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        Try this

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I think that substr   throws an exception if str only contains the whitespace    I would modify it to the following code   string trim string amp  str        size t first   str find first not of           if  first    std  string  npos          return         size t last   str find last not of           return str substr first   last-first 1

[c++] Trim whitespace from a String

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