Thread: Functions for C strings

Originally Posted by officedog

Code:

buffer = realloc(buffer, sizeof(char) * baseSize);

I guess I should also add a test for a NULL pointer too

Yes, much better. And just nit-picking here, but you could probably bypass the part that makes a smaller copy by simply starting with a smaller buffer size (say 8 or 16, maybe). Just a thought.

Really appreciate the help. Thanks. Just for completeness, I post the final(ish) version of the function. I made initial buffer as 64 to decrease likelihood of resizing

Code:

char * GC_GetUserInputDyanmicV2() {
    int baseSize =  64;
    char c;
    
    //dynamic allocation of buffer
    char * buffer = malloc(sizeof(char) * baseSize);
    if (buffer == NULL) {
        return buffer;
    }
    
    int index = 0;
    
    while ((c = fgetc(stdin)) != '\n'  && c != EOF) {
        //resize buffer if not enough room
        if (index > baseSize -2) {
            baseSize += baseSize;
            buffer = realloc(buffer, sizeof(char) * baseSize);
            if (buffer == NULL) {
                return NULL;
            }
        }
        buffer[index] = c;
        index++;
    }
    //adds '\0' to end of the string (needed for string functions)
    buffer[index] = '\0';
    
    //checks length of string
    int len = strlen(buffer);
    printf("\nLength of final string (without 0) = %d", len);
    
    //Dynamic allocation of correct sized memory
    char * stringReturn = malloc(sizeof(char) * (len + 1) );
    
    //copies buffer to return string
    strncpy(stringReturn, buffer, len+1);
    //adds '\0' to end of return string
    stringReturn[len] = '\0';
    
    //frees buffer
    free(buffer);
    buffer = NULL;
    
    return stringReturn;
}

Looks fine, except that you might want to check that malloc didn't return NULL in allocating 'stringReturn'.

oh yes, missed that one. updated version:

Code:

char * GC_GetUserInputDyanmicV2() {
    int baseSize =  64;
    char c;
    
    char * buffer = malloc(sizeof(char) * baseSize);
    if (buffer == NULL) {
        return buffer;
    }
    
    int index = 0;
    
    while ((c = fgetc(stdin)) != '\n'  && c != EOF) {
        if (index > baseSize -2) {
            
            baseSize += baseSize;
            buffer = realloc(buffer, sizeof(char) * baseSize);
            if (buffer == NULL) {
                return NULL;
            }
            printf("\nReallocated space: baseSize = %d, index = %d", 
                   baseSize, index);
            
        }
        buffer[index] = c;
        index++;
    }
    //adds '\0' to end of the string (needed for string functions)
    buffer[index] = '\0';
    
    //checks length of string
    int len = strlen(buffer);
    printf("\nLength of final string (without 0) = %d", len);
    
    //Dynamic allocation of correct sized memory
    char * stringReturn = malloc(sizeof(char) * (len + 1) );
    if (stringReturn == NULL) {
        return NULL;
    }
    
    //copies buffer to return string
    strncpy(stringReturn, buffer, len+1);
    //adds '\0' to end of return string
    stringReturn[len] = '\0';
    
    //frees buffer
    free(buffer);
    buffer = NULL;
    
    return stringReturn;
}