give a look into my TRIM function (please comment)

This is a discussion on give a look into my TRIM function (please comment) within the C Programming forums, part of the General Programming Boards category; hey guys! this is my first pointers act. just learning about pointers. I need you guys say me something about ...

  1. #1
    aze
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    give a look into my TRIM function (please comment)

    hey guys! this is my first pointers act. just learning about pointers.
    I need you guys say me something about this function.
    Is it good? what should I improve?
    Code:
    #include <stdio.h>
    #include <string.h>
    #include <ctype.h>
    
    char *trim_str(char *string);
    
    void main()
    {
    	char s[] = "   	string teste   	   ";
    	printf("--%s--",trim_str(s));
    }
    
    char *trim_str(char *string){ /*remove spaces before*/
    	char *a;
    
    	if (isspace(*string)){
    		while (isspace(*string++));
    		string--;
    		trim_str(string); /*2nd call to remove spaces after*/
    	} else { /*remove spaces after*/
    		a = string + (strlen(string)-1);
    		while (isspace(*a--));
    		a+=2;
    		*a='\0';
    	}
    	return(string);
    }

  2. #2
    Registered User Codeplug's Avatar
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    >> Is it good?
    Code:
    trim_str(s);
    printf("--%s--", s);
    Modify and return the parameter.

    >> what should I improve?
    Don't use recursion.

    gg

  3. #3
    and the hat of wrongness Salem's Avatar
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    don't use void main either

    It would be a good idea to provide an additional buffer of where you want the trimmed string stored. Modifying strings "in place" is a bit anti-social (especially in large programs where it may go unnoticed for a while).
    You cannot for example trim
    Code:
    char *s= "   	string teste   	   ";
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  4. #4
    aze
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    hey thank you guys!
    im a newbie

    Modify and return the parameter.

    Don't use recursion.
    What is wrong with recursion? How should I change it?

    -------------------------------------------------------
    You cannot for example trim
    Code:

    char *s= " string teste ";
    and how would I change it?

    please guys! post your code suggestions!

  5. #5
    Guest Sebastiani's Avatar
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    The function returns a pointer that may not point to the first element in the array - not a good idea at all! If the array was dynamically allocated that would certainly lead to a memory leaks. Instead, move the desired data to the beginning of the array, and be sure to return a pointer to the first element.
    Code:
    if( numeric_limits< byte >::digits != bits_per_byte )
        error( "program requires bits_per_byte-bit bytes" );
    24bbs.cpp

  6. #6
    Code Goddess Prelude's Avatar
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    >What is wrong with recursion?
    It doesn't really simplify the problem to use recursion, and you can easily just use two loops to do the same thing.

    >How should I change it?
    Use loops:
    Code:
    #include <stdio.h>
    #include <string.h>
    #include <ctype.h>
    
    char *trim_str(char *string);
    
    int main()
    {
      char s[] = "   	   ";
      printf("--%s--",trim_str(s));
      return 0;
    }
    
    char *trim_str(char *string){
      char *a;
    
      while ( *string && isspace ( *string ) ) {
        string++;
      }
      a = string + ( strlen ( string ) - 1 );
      while ( a != string && isspace ( *a ) ) {
        a--;
      }
      if ( *a != '\0' )
        a[1] = '\0';
    
      return(string);
    }
    >and how would I change it?
    String literals cannot be portably modified. To fix your code to handle them you will need to either do some dynamic memory allocation, or require the caller to pass a buffer large enough to hold the trimmed string.
    My best code is written with the delete key.

  7. #7
    Registered User Codeplug's Avatar
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    >> Modify and return the parameter.
    That means what Sebastiani said. Or in other words, the pointer address that passed in should be the pointer address that's returned.
    Otherwise, you can change your API so that the caller is responsible for providing the output buffer to store the trimmed result as Salem suggested.

    >> What is wrong with recursion?
    Nothing wrong with it, it's just over kill in this situation.
    You're using recursion for a simple two-step process: trim the beggining then trim the end.

    >> post your code suggestions!
    We are
    You seem more than capable of implementing our suggestions.

    gg

    [EDIT]
    Late posting...

  8. #8
    aze
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    i changed it. now the function do not returns a pointer. now it change the string directly on its location:
    Code:
    #include <string.h>
    #include <ctype.h>
    
    void trim_str(char *string);
    
    int main(){
    	char str[] = "     	string test   	";
    	
    	trim_str(str);
    	
    	printf("-%s-", str );
    	
    	return(0);
    }
    
    
    void trim_str(char *string){
    	char *a;
    	a = string;
    	if (isspace(*string)){
    		while (isspace(*a++)); /* set pointer to the first non-space char */
    		a-=2;
    		while (*a++ != '\0'){
    			*string = *a;
    			string++;
    		}
    		string-=(a-string); /*reset pointer to startup pos*/
    	}
    	string+=strlen(string)-1; /* set pointer to the last char */
    	while(isspace(*string--));
    	string+=2;	
    	*string='\0';
    }
    please, comment it!
    Last edited by aze; 04-21-2004 at 12:18 PM.

  9. #9
    ATH0 quzah's Avatar
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    If you want a safe implementation, you should be passing a buffer to copy the info into. Otherwise, again, string literals will do BadThingsTM.
    Code:
    trim_str("  BadThingsTM    " );
    Also, you can simplify this a bit...
    Code:
    void trim( char *O0OO, char *O00O )
    {
            char *O000 = O0OO;
            char *OO0O = O000+strlen(O0OO)-1;
            while( isspace( *O000 ) ) O000++;
            while( isspace( *OO0O ) ) OO0O--;
            while( O000 <= OO0O )
                    *O00O++ = *O000++;
    }
    Something like that, assuming I'm reading your problem right. However, you'll not want to turn that in for homework.

    Quzah.
    Hope is the first step on the road to disappointment.

  10. #10
    Guest Sebastiani's Avatar
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    One thing I noticed was some unnecessary math that could be eliminated by using better structured loops. For instance:


    Code:
    while (isspace(*a++)); 
    		a-=2;
    		while (*a++ != '\0'){
    			*string = *a;
    			string++;
    		}

    Could be made more readable using something like:


    Code:
    while (isspace(*a)) a++; 
    		while (*a != '\0'){
    			*string = *a;
    			string++, a++;
    		}

    Otherwise, the function looks good. Here's another version of the function:


    Code:
     char * trim(char * str)
    {
     int length = strlen(str);
    
         if(length > 0)
        {
         char * data = str;
         char * front = str;
         char * back = str[length];
    
         while(isspace(*front))  ++front;
    
         while(isspace(*(back-1)))  --back; 
    
         while(front < back)  *(data++) = *(front++);  
    
         *data = 0;
        } 
    
     return str;
    }
    Code:
    if( numeric_limits< byte >::digits != bits_per_byte )
        error( "program requires bits_per_byte-bit bytes" );
    24bbs.cpp

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