trim string function (code)

Hi all! I coded this function to eliminate spaces before and after a string.
e.g.:

Code:

trim("       just a test    123      ");

will return

Code:

"just a test    123"

But I didn't uderstand why the compiler ask for *trim instead of trim.
Any improvement/suggestion is welcome.

Code:

char *trim(char string[100])
{
	int a, b, c, d; 
	char trimed_string[100];
	a = b = c = d = 0;
	
	for (a; a < strlen(string); a++)
	{
		if (string[a]!=' ' && !b) /* first valid char */
			b = a;
		if (string[a]==' ' && b)
		{
			for (d; d < strlen(string)-a;d++)
				if (string[d+a]!=' ')
					c = a+d;
		}
	}

	a=0;
	for (b; b <= c; b++)
	{
		trimed_string[a]= string[b];
		a++;
	}
	trimed_string[ strlen(trimed_string)-10 ] ='\0'; // why -10 ? otherwise it'll return junk
	return(trimed_string);
}

I just tested with another string and there's something wrong with this line:

Code:

trimed_string[ strlen(trimed_string)-10 ] ='\0';

output of

Code:

trim("    test12      3  3     4   ")

Code:

test12      3  3     4Ûw╗hÛ

There's something wrong with the string termination '\0';

Your code is entirely too complicated for the task at hand, and it's also incorrect. You get garbage when you return because you cannot return a pointer to a local variable, so trimed_string is off limits for a return value. A simpler solution would be to find the first non-space index, the last non-space index, and copy that slice to the beginning of the string. Terminate with a nul and you're done:

Code:

char *tr ( char *s )
{
  int i = 0;
  int j = strlen ( s ) - 1;
  int k = 0;

  while ( isspace ( s[i] ) && s[i] != '\0' )
    i++;

  while ( isspace ( s[j] ) && j >= 0 )
    j--;

  while ( i <= j )
    s[k++] = s[i++];

  s[k] = '\0';

  return s;
}

-Prelude

you function is better.
but I still not understand why my function returned junk after the string.

>but I still not understand why my function returned junk after the string.

Code:

char *f()
{
  /* Memory is allocated for the local array a */
  char a[] = "Some string";

  /* The address of a is returned to the caller */
  return a;
}
/* After f returns the memory for a is reclaimed. */

int main ( void )
{
  char *p = f();
  /* Since the memory for a was reclaimed, p now points to released memory */

  return 0;
}

-Prelude

how about strtok.

char *tokchar;
tokchar = strtok(trim_string, " ");
while(tokchar != NULL){

printf////////

tokchar = strtok(NULL, " ");
}

>how about strtok.
That won't work as you would expect if there are internal spaces. The original question was about removing leading and trailing whitespace while leaving everything else intact.

-Prelude

>>trim(" just a test 123 ");
Don't forget, you cannot safely modify the data passed in by this function call, as its a string literal.

Here's yet another example:

Code:

char * normalize(char * string){
 char * s, * i;
 int ready = FALSE;
 
    for(i = s = string; *i; ++i)
   {

       if(isspace(*i))
      {
          if(!ready)
         {
          continue;
         }
          else ready = FALSE;
      }
       else ready = TRUE;

    *(s++) = *i;
   }

 *s = 0;
 return string;
}







int main(){
 char string[] = "   I        think,    therefore    I          am.";
 printf("Before:\n%s\n",string);
 printf("After:\n%s", normalize(string));
 getch();
 return 0;
}

Code:

if(isspace(*i))
{
    if(!ready)
    {
        continue;
    }
    else ready = FALSE;
}
else ready = TRUE;

There is no need for the continue.

Code:

ready = isspace(*i) ? FALSE ? TRUE;

Or drawn out...

Code:

if( isspace(*i) )
    ready = FALSE;
else
    ready = TRUE;

There really is no need to check the ready state once you do the isspace() check, since either way, if it is a space, ready gets set to FALSE. So just do it in one step.

Speed wise, this is probably faster anyway:

Code:

check isspace
    check ready state
        continue
    else check ready state
        ready = FALSE
else isspace
    ready = TRUE;

1 check 1 assignment OR 2 checks 1 assignment

Versus:

Code:

check isspace
    ready = FALSE
else isspace
    ready = TRUE

1 check, 1 assignment every time through.

Quzah.