pointer functions - nebie question

This is a discussion on pointer functions - nebie question within the C Programming forums, part of the General Programming Boards category; Hi all say I have this function: char *trim(char *string) If I understand it correctly the function's result value has ...

  1. #1
    Registered User
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    Mar 2006
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    pointer functions - nebie question

    Hi all
    say I have this function:
    char *trim(char *string)

    If I understand it correctly the function's result value has to be allocated, let's say, by malloc. But how is this allocation going to be freed? All I do in my program is this:

    string = trim(string)

    Thanks in advance

    Here is the function
    Code:
    char *
    trim (char *string)
    {
      char *result = 0;
    
      /* Ignore NULL pointers.  */
      if (string)
        {
          char *ptr = string;
    
          /* Skip leading whitespace.  */
          while (strchr (WHITESPACE_STR, *ptr))
            ++ptr;
    
          /* Make a copy of the remainder.  */                     
          if ((result = (char *) malloc(strlen(ptr)+1)) == NULL)   
         {                                                        
            fprintf(stderr,"trim() - Cannot allocate; %s",ptr);    
            return NULL;                                           
         }                                                        
         memset(result,'\0',strlen(ptr)+1);                       
         strcpy(result,ptr);                                      
    
          /* Move to the last character of the copy.  */
          for (ptr = result; *ptr; ++ptr)
            /* NOWORK */;
          --ptr;
    
          /* Remove trailing whitespace.  */
          for (--ptr; strchr (WHITESPACE_STR, *ptr); --ptr)
              *ptr = '\0';
       }
    
      return result;
    }

  2. #2
    Gawking at stupidity
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    The calling function would have to free() the memory. Alternatively, you could pass a buffer to your trim() function in which the trimmed string is stored. Or, if you're not concerned with keeping a pure copy of the string you could just hack up the original string in the function.
    If you understand what you're doing, you're not learning anything.

  3. #3
    Mad OnionKnight's Avatar
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    free(string);

  4. #4
    Registered User
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    Mar 2006
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    I guess it wouldn't be a good design for the calling function to free memory that was allocated in the called function. Since the trimmed value could not be bigger than the *string parameter, I will free the allocated memory in the trim function itself and copy the result value back to the string parameter.

    Thanks a lot

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