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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
Old 10-09-2008
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.
 

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Ns_String(3aolserver)					   AOLserver Library Procedures 				     Ns_String(3aolserver)

__________________________________________________________________________________________________________________________________________________

NAME
Ns_Match, Ns_NextWord, Ns_StrCaseFind, Ns_StrCopy, Ns_StrDup, Ns_StrNStr, Ns_StrToLower, Ns_StrToUpper, Ns_StrTrim, Ns_StrTrimLeft, Ns_Str- TrimRight, Ns_StringPrint, ns_strcopy, ns_strdup - library procedures SYNOPSIS
#include "ns.h" char * Ns_Match(char *a, char *b) char * Ns_NextWord(char *line) char * Ns_StrCaseFind(char *s1, char *s2) char * Ns_StrCopy(char *str) ns_strcopy(char *str) char * Ns_StrDup(char *str) ns_strdup(char *str) char * Ns_StrNStr(char *pattern, char *expression) char * Ns_StrToLower(char *string) char * Ns_StrToUpper(char *string) char * Ns_StrTrim(char *string) char * Ns_StrTrimLeft(char *string) char * Ns_StrTrimRight(char *string) void Ns_StringPrint(char *string) _________________________________________________________________ DESCRIPTION
Ns_Match(a, b) Compare the beginnings of two strings, case insensitively. The comparison stops when the end of the shorter string is reached. Return NULL if no match, b if match. Ns_NextWord(line) Return a pointer to first character of the next word in a string; words are separated by white space. The returned pointer points into the original string. For example, Ns_NextWord("abc def") returns a pointer to the 'd' in that string. Ns_StrCaseFind(s1, s2) Locate the first occurrence of substring s2 within string s1 in a case-insensitive manner. The terminating ' ' characters are not compared. Returns a pointer that points into s1. Uses strstr(3) to do its work. Ns_StrCopy(str) ns_strcopy(str) Copy a string or NULL value using Ns_Malloc. The Ns_StrCopy function is identical to the Ns_StrDup function but allows for the string parameter to be NULL, in which case Ns_StrCopy does nothing and returns NULL. Ns_StrDup(str) ns_strdup(str) Copy a string using Ns_Malloc. The Ns_StrDup function calls Ns_Malloc to allocate enough memory to make a copy of the given string. Ns_StrNStr(pattern, expression) Search through pattern for expression, case insensitively. Return a pointer that points to where the match begins within pattern, or NULL if expression is not contained in pattern. Ns_StrToLower(string) Convert string to lowercase. Returns pointer to original string. Original string will be modified. Ns_StrToUpper(string) Convert string to uppercase. Returns pointer to original string. Original string will be modified. Ns_StrTrim(string) Trim leading and trailing white space from string. A pointer to the trimmed string will be returned, which will be in the original string. Do not lose your original pointer to the string if you later need to free it. Ns_StrTrimLeft(string) Trim leading white space from string. A pointer to the trimmed string will be returned, which will be in the original string. Do not lose your original pointer to the string if you later need to free it. Ns_StrTrimRight(string) Trim trailing white space from string. The original string pointer will be returned, but the string will have been modified: a ' 's will have been placed right after the last non-whitespace character of the string. Ns_StringPrint(string) Print a string to stdout. SEE ALSO
nsd(1), info(n) KEYWORDS
AOLserver 4.0 Ns_String(3aolserver)
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