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Top Forums Programming How to trim the white space around a string in C program Post 302248304 by calv on Friday 17th of October 2008 09:05:54 AM
Old 10-17-2008
error in trim_copy() was a typo: "ouput" -> "output" (but no segfault)

error in trim_nocopy() was an undeclared variable (that also needs to be initialized. segfault, if the new variable is not initialized and the string contains no nonspace characters)

btw. trim_nocopy() has no real practical reason to exist. It is only to show that a left trimming can be done without writing to the string at all, just by changing the start pointer. Also right trimming can be done by just writing a zero after the last nonspace. In fact the trim_copy() function is the one you should always use, both for in place (input==output) or copying operations. Also it makes sense to switch the parameters, so they are in sync with other c std lib string functions like strcpy() and strcat().

ok, now the fixed version:

Code:
void trim_copy(char *input, char *output)
{
  char *end = output;
  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;
  }

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

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

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

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

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

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

  return start;
}

 

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STRING(3)						     Library Functions Manual							 STRING(3)

NAME
strcat, strncat, strcmp, strncmp, strcpy, strncpy, strlen, index, rindex - string operations SYNOPSIS
char *strcat(s1, s2) char *s1, *s2; char *strncat(s1, s2, n) char *s1, *s2; strcmp(s1, s2) char *s1, *s2; strncmp(s1, s2, n) char *s1, *s2; char *strcpy(s1, s2) char *s1, *s2; char *strncpy(s1, s2, n) char *s1, *s2; strlen(s) char *s; char *index(s, c) char *s, c; char *rindex(s, c) char *s; DESCRIPTION
These functions operate on null-terminated strings. They do not check for overflow of any receiving string. Strcat appends a copy of string s2 to the end of string s1. Strncat copies at most n characters. Both return a pointer to the null-termi- nated result. Strcmp compares its arguments and returns an integer greater than, equal to, or less than 0, according as s1 is lexicographically greater than, equal to, or less than s2. Strncmp makes the same comparison but looks at at most n characters. Strcpy copies string s2 to s1, stopping after the null character has been moved. Strncpy copies exactly n characters, truncating or null- padding s2; the target may not be null-terminated if the length of s2 is n or more. Both return s1. Strlen returns the number of non-null characters in s. Index (rindex) returns a pointer to the first (last) occurrence of character c in string s, or zero if c does not occur in the string. BUGS
Strcmp uses native character comparison, which is signed on PDP11's, unsigned on other machines. STRING(3)
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