Do I need to free the strtok resulting string?

Sunspawn picture Sunspawn · Jan 3, 2014 · Viewed 15.8k times · Source

Or rather, how does strtok produce the string to which it's return value points? Does it allocate memory dynamically? I am asking because I am not sure if I need to free the token in the following code:

The STANDARD_INPUT variables is for exit procedure in case I run out of memory for allocation and the string is the tested subject.

int ValidTotal(STANDARD_INPUT, char *str)
{
    char *cutout = NULL, *temp, delim = '#';
    int i = 0; //Checks the number of ladders in a string, 3 is the required number
    temp = (char*)calloc(strlen(str),sizeof(char));
    if(NULL == temp)
        Pexit(STANDARD_C); //Exit function, frees the memory given in STANDARD_INPUT(STANDARD_C is defined as the names given in STANDARD_INPUT)
    strcpy(temp,str);//Do not want to touch the actual string, so copying it
    cutout = strtok(temp,&delim);//Here is the lynchpin - 
    while(NULL != cutout)
    {
        if(cutout[strlen(cutout) - 1] == '_')
            cutout[strlen(cutout) - 1] = '\0'; \\cutout the _ at the end of a token
        if(Valid(cutout,i++) == INVALID) //Checks validity for substring, INVALID is -1
            return INVALID;
        cutout = strtok(NULL,&delim);
        strcpy(cutout,cutout + 1); //cutout the _ at the beginning of a token
    }
    free(temp);
return VALID; // VALID is 1
}

Answer

Andreas picture Andreas · Jan 3, 2014

strtok manipulates the string you pass in and returns a pointer to it, so no memory is allocated.

Please consider using strsep or at least strtok_r to save you some headaches later.