Removing Spaces from a String in C

Question

What is the easiest and most efficient way to remove spaces from a string in C

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if you are still interested  this function removes spaces from the beginning of the string  and I just had it working in my code   void removeSpaces char  str1          char  str2       str2 str1        while   str2       str2          if  str2  str1  memmove str1 str2 strlen str2  1

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Code taken from zString library     search for character  s     int zstring search chr char  token char s           if   token    s    0           return 0       for    token  token            if   token    s              return 1       return 0     char  zstring remove chr char  str const char  bad        char  src   str    dst   str          validate input        if    str  amp  amp  bad           return NULL       while  src          if zstring search chr bad  src               src            else              dst      src        assign first  then incement          dst   0       return str      Code example    Exmaple Usage       char s    this is a trial string to test the function          char  d             printf   s n  zstring remove chr s d       Example Output       thisisatrialstringtotestthefunction   Have a llok at the zString code  you may find it useful https   github com fnoyanisi zString

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As we can see from the answers posted  this is surprisingly not a trivial task  When faced with a task like this  it would seem that many programmers choose to throw common sense out the window  in order to produce the most obscure snippet they possibly can come up with   Things to consider    You will want to make a copy of the string  with spaces removed  Modifying the passed string is bad practice  it may be a string literal  Also  there are sometimes benefits of treating strings as immutable objects  You cannot assume that the source string is not empty  It may contain nothing but a single null termination character  The destination buffer can contain any uninitialized garbage when the function is called  Checking it for null termination doesn t make any sense  Source code documentation should state that the destination buffer needs to be large enough to contain the trimmed string  Easiest way to do so is to make it as large as the untrimmed string  The destination buffer needs to hold a null terminated string with no spaces when the function is done  Consider if you wish to remove all white space characters or just spaces      C programming isn t a competition over who can squeeze in as many operators on a single line as possible  It is rather the opposite  a good C program contains readable code  always the single-most important quality  without sacrificing program efficiency  somewhat important   For this reason  you get no bonus points for hiding the insertion of null termination of the destination string  by letting it be part of the copying code  Instead  make the null termination insertion explicit  to show that you haven t just managed to get it right by accident    What I would do   void remove spaces  char  restrict str trimmed  const char  restrict str untrimmed      while   str untrimmed      0           if  isspace  str untrimmed                str trimmed    str untrimmed        str trimmed              str untrimmed           str trimmed     0       In this code  the source string  str untrimmed  is left untouched  which is guaranteed by using proper const correctness  It does not crash if the source string contains nothing but a null termination  It always null terminates the destination string   Memory allocation is left to the caller  The algorithm should only focus on doing its intended work  It removes all white spaces   There are no subtle tricks in the code  It does not try to squeeze in as many operators as possible on a single line  It will make a very poor candidate for the IOCCC  Yet it will yield pretty much the same machine code as the more obscure one-liner versions   When copying something  you can however optimize a bit by declaring both pointers as restrict  which is a contract between the programmer and the compiler  where the programmer guarantees that the destination and source are not the same address  or rather  that the data they point to are only accessed through that very pointer and not through some other pointer   This allows more efficient optimization  since the compiler can then copy straight from source to destination without temporary memory in between

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include  lt ctype gt   char   remove spaces char   source  char   target         while  source    amp  amp   target                 if   isspace  source                  target      source              return target      Notes    This doesn t handle Unicode

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include lt stdio h gt   include lt string h gt  main       int i 0 n    int j 0    char str            Nar ayan singh                   char  ptr  ptr1    printf  sizeof str  ld n  strlen str      while str i                  memcpy  str str 1 strlen str  1          printf  sizeof str  ld n  strlen str      n strlen str     while str n          str n     0       n--    str n 1    0     printf  str  s   str     printf  sizeof str  ld n  strlen str

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The easiest and most efficient way to remove spaces from a string is to simply remove the spaces from the string literal  For example  use your editor to  find and replace   hello     world  with  helloworld   and presto   Okay  I know that s not what you meant  Not all strings come from string literals  right  Supposing this string you want spaces removed from doesn t come from a string literal  we need to consider the source and destination of your string    We need to consider your entire algorithm  what actual problem you re trying to solve  in order to suggest the simplest and most optimal methods   Perhaps your string comes from a file  e g  stdin  and is bound to be written to another file  e g  stdout   If that s the case  I would question why it ever needs to become a string in the first place  Just treat it as though it s a stream of characters  discarding the spaces as you come across them      include  lt stdio h gt   int main void        for                int c   getchar            if  c    EOF    break               if  c           continue            putchar c             By eliminating the need for storage of a string  not only does the entire program become much  much shorter  but theoretically also much more efficient

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I assume the C string is in a fixed memory  so if you replace spaces you have to shift all characters   The easiest seems to be to create new string and iterate over the original one and copy only non space characters

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I came across a variation to this question where you need to reduce multiply spaces into one space  represent  the spaces   This is my solution   char str      Put Your string Here         int copyFrom   0  copyTo   0   printf  Start String  s n   str    while  str copyTo     0        if  str copyFrom                    str copyTo    str copyFrom           copyFrom            copyTo             while   str copyFrom           amp  amp   str copyFrom      0                  copyFrom                         str copyTo    str copyFrom        if  str copyTo       0             copyFrom            copyTo             printf  Final String  s n   str     Hope it helps  -

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Here s a very compact  but entirely correct version   do while isspace  s   s    while  d      s         And here  just for my amusement  are code-golfed versions that aren t entirely correct  and get commenters upset   If you can risk some undefined behavior  and never have empty strings  you can get rid of the body   while   d   isspace  s        s     Heck  if by space you mean just space character   while   d   s          s     Don t use that in production

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Here is the simplest thing i could think of  Note that this program uses second command line argument  argv 1   as a line to delete whitespaces from    include  lt string h gt   include  lt stdio h gt   include  lt stdlib h gt     The function itself with debug printing to help you trace through it     char  trim const char  str        char  res   malloc sizeof str    1       char  copy   malloc sizeof str    1       copy   strncpy copy  str  strlen str    1       int index   0       for  int i   0  i  lt  strlen copy    1  i              if  copy i                                res index    copy i               index                      printf  End of iteration  d n   i           printf  Here is the initial line   s n   copy           printf  Here is the resulting line   s n   res           printf   n              return res     int main int argc  char  argv            trim function test      const char  line   argv 1       printf  Here is the line   s n   line        char  res   malloc sizeof line    1       res   trim line        printf   nAnd here is the formatted line   s n   res        return 0

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That s the easiest I could think of  TESTED  and it works    char message 50   fgets message  50  stdin   for  i   0  j   0  i  lt  strlen message   i             message i-j    message i           if message i                      j      message i      0

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Easiest and most efficient don t usually go together     Here s a possible solution   void remove spaces char  s        const char  d   s      do           while   d                         d                  while   s      d

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In C  you can replace some strings in-place  for example a string returned by strdup     char  str   strdup   a b c      char  write   str   read   str  do      if   read                 write      read    while   read      printf   s n   str     Other strings are read-only  for example those declared in-code   You d have to copy those to a newly allocated area of memory and fill the copy by skipping the spaces   char  oldstr     a b c     char  newstr   malloc strlen oldstr  1   char  np   newstr   op   oldstr  do      if   op                 np      op    while   op      printf   s n   newstr     You can see why people invented other languages

[c] Removing Spaces from a String in C?

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