Parsing a string in C with strsep (alternative methods)

c, parsing, strsep, valgrind

Solution

`strsep` overwrites the target of its first (pointer-to-pointer) argument, so you lose the pointer to the `malloc`'d buffer's base. In fact, if you were do put a `printf("%p\n", r);` just before the `free`, you'd find out that you're freeing a null pointer, which has no effect.

The easy solution is to introduce an additional variable to keep that pointer around and `free` it when you're done. Idiomatic usage would be

char *r = strdup("Marco:Q:3F7PKC");
// check for errors

char *tok = r, *end = r;
while (tok != NULL) {
    strsep(&end, ":");
    puts(tok);
    tok = end;
}

free(r);

Problem

I want to parse a string, and I use `strsep` function: ``` #include <stdio.h> #include <stdlib.h> #include <string.h> int main() { char str[] = "Marco:Q:2F7PKC"; char *token1, *token2, *token3; char *r = malloc(30); strcpy(r, str); token1 = strsep(&r, ":"); token2 = strsep(&r, ":"); token3 = strsep(&r, ":"); printf("tok1 = %s\n", token1); printf("tok2 = %s\n", token2); printf("tok3 = %s\n", token3); free(r); return 0; } ``` The function do its job well, but If I launch valgrind, the allocated string `char * r` does not freed correctly (definitely lost: 30 bytes in 1 blocks). I'd like to know why and if there are alternative way to do the same thing, maybe without call strsep. I call valgrind with `valgrind --tool=memcheck --leak-check=full --show-reachable=yes ./a.out`

Original source