Question

So I wrote the following code in linux(Ubuntu) using the emacs text editor it basically supposed to split the string on the delimeter passed in . When I ran it it segfaulted I ran it though GDB and it gives me an error at strcpy(which I don’t invoke) but is probably done implicitly in sprintf. I didn’t think I was doing anything wrong so I booted into windows and ran it through visual studio and it works fine I am new to writing C in Linux and know the problem is in the While loop where i call sprintf() (which is odd because the call outside of the loop writes without causing an error) to write the token to the array. If anyone can tell me where I am going wrong I would greatly appreciate it. Here is the code

/*    split()
 Description:
 - takes a string and splits it into substrings "on" the 
 <delimeter>*/
void split(char *string, char *delimiter)
{
    int i;
    int count = 0;
    char *token;

    //large temporary buffer to over compensate for the fact that we have
    //no idea how many arguments will be passed with a command
    char *bigBuffer[25];

    for(i = 0; i < 25; i++)
    {
        bigBuffer[i] = (char*)malloc(sizeof(char) * 50);
    }

    //get the first token and add it to <tokens> 
    token = strtok(string, delimiter);
    sprintf(bigBuffer[0], "%s", token);

    //while we have not encountered the end of the string keep
    //splitting on the delimeter and adding to <bigBuffer>
    while(token != NULL)
    {
        token = strtok(NULL, delimiter);
        sprintf(bigBuffer[++count], "%s", token);
    }

    //for(i = 0; i < count; i++)
    //printf("i = %d : %s\n", i, bigBuffer[i]);
    for(i = 0; i< 25; i++)
    {
        free(bigBuffer[i]);
    }

} //end split()

Answer 1

You aren’t checking for NULL from the return of strtok on the last iteration of the loop … so strtok can return NULL, yet you still pass the NULL value in the token pointer to sprintf.

Change your while-loop to the following:

while(token = strtok(NULL, delimiter)) sprintf(bigBuffer[++count], "%s", token);

That way you can never pass a NULL pointer to strtok because the while-loop NULL-pointer check will enforce that token always has a valid value when sprintf is called with it as an argument.