How to trim the white space around a string in C program Post: 302244994

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Top Forums Programming How to trim the white space around a string in C program Post 302244994 by calv on Thursday 9th of October 2008 05:49:42 AM

10-09-2008

Registered User

This is all just overkill. There are three variants to do trimming in C:

1. Output in another place

Code:

void trim_copy(char *input, char *output)
{
  char *end = ouput;
  char c;

  // skip spaces at start
  while(*input && isspace(*input))
    ++input;

  // copy the rest while remembering the last non-whitespace
  while(*input)
  {
    // copy character
    c = *(output++) = *(input++);

    // if its not a whitespace, this *could* be the last character
    if( !isspace(c) )
      end = output;
  }

  // white the terminating zero after last non-whitespace
  *end = 0;
}

2. In place

Code:

void trim_inplace(char *s)
{
  trim_copy(s, s);
 }

3. In place, but avoid copying by shifting string pointer

Code:

char *trim_nocopy(char *s)
{
  char *start = s;

   // skip spaces at start
  while(*start && isspace(*start))
    ++start;

  char *i = start
  // iterate over the rest remebering last non-whitespace
  while(*i)
  {
    if( !isspace(*(i++)) )
      end = i;
  }

  // white the terminating zero after last non-whitespace
  *end = 0;

  return start;
}

All three solutions are O(n). Use in place if you don't need the original anymore (and it's not constant like a literal). If you use new or malloc to allocate memory, then delete/free the original pointer in case 3, not the returning value.

calv

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LEARN ABOUT NETBSD

isspace

ISSPACE(3)						   BSD Library Functions Manual 						ISSPACE(3)

NAME

     isspace -- white-space character test

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <ctype.h>

     int
     isspace(int c);

DESCRIPTION

     The isspace() function tests for the standard white-space characters for which isalnum(3) is false.  The standard white-space characters are
     the following:

	   ' '	  Space character.
	   f	  Form feed.
	   
	  New-line.
	   
	  Carriage return.
	   		  Horizontal tab.
	   v	  And vertical tab.

     In the ``C'' locale, isspace() returns true only for the standard white-space characters.

RETURN VALUES

     The isspace() function returns zero if the character tests false and returns non-zero if the character tests true.

SEE ALSO

     ctype(3), isalnum(3), isalpha(3), isascii(3), isblank(3), iscntrl(3), isdigit(3), isgraph(3), islower(3), isprint(3), ispunct(3), isupper(3),
     isxdigit(3), stdio(3), toascii(3), tolower(3), toupper(3), ascii(7)

STANDARDS

     The isspace() function conforms to ANSI X3.159-1989 (``ANSI C89'').

CAVEATS

     The argument to isspace() must be EOF or representable as an unsigned char; otherwise, the behavior is undefined.	See the CAVEATS section of
     ctype(3) for more details.

BSD
								  April 17, 2008							       BSD

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LEARN ABOUT NETBSD

isspace