Question

I have written the following program to resolve a path to several directory names

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *
tokenizer(char *path, char **name){
  char s[300];
  char *buffer;
  memcpy(s, path, strlen(path)+1);
  printf("%s\n",s);    // PROBLEM
  int i=0;
  while(s[i] == '/'){
    i++;
  }
  if (i == strlen(path)){
    return NULL;
  }
  *name = strtok_r(s, "/", &buffer);
  return buffer;
}

int main(void){
  char str[300];
  char *token, *p;
  scanf("%s",str);
  p = tokenizer(str, &token);
  if (p != NULL)
    printf("%s\n",token);
  else
    printf("Nothing left\n");
  while((p=tokenizer(p, &token)) != NULL){
    printf("%s\n",token);
  }
}

Output of the above program

Input: a/b/c
Output: a/b/c
a/b/c
a
b/c
b
c
c

If I comment the line labelled PROBLEM

Input: a/b/c
Output: Some garbage value

Can somebody explain me the reason for this strange behavior?

Note:
I have realised that s is a stack allocated variable and it ceases to exist in function main() but why does the program works when I use printf() ?

Answer 1

In addition to what geekasaur says:

strtok_r‘s 3rd parameter is used incorrectly, in two ways:
1. It should be initialized to NULL before the first call.
2. It shouldn’t be used in any way (you return it to the caller). It should only be passed to another strtok_r call.