Why does the following C program give a bus error?

Question

I think it's the very first strtok call that's failing. It's been a while since I've written C and I'm at a loss. Thanks very much.

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

int main(int argc, char **argv) {
  char *str = "one|two|three";

  char *tok = strtok(str, "|");

  while (tok != NULL) {
    printf("%s\n", tok);
    tok = strtok(NULL, "|");
  }

  return 0;
}

Answer 1

String literals should be assigned to a const char*, as modifying them is undefined behaviour. I'm pretty sure that strtok modifies it's argument, which would explain the bad things that you see.

Answer 2

There are 2 problems:

1. Make str of type char[]. GCC gives the warning foo.cpp:5: warning: deprecated conversion from string constant to ‘char*’ which indicates this is a problematic line.

2. Your second strtok() call should have NULL as its first argument. See the docs.

The resulting working code is:

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

int main(int argc, char **argv) {
  char str[] = "one|two|three";

  char *tok = strtok(str, "|");

  while (tok != NULL) {
    printf("%s\n", tok);
    tok = strtok(NULL, "|");
  }

  return 0;
}

which outputs

one
two
three

Answer 3

I'm not sure what a "bus" error is, but the first argument to strtok() within the loop should be NULL if you want to continue parsing the same string.

Otherwise, you keep starting from the beginning of the same string, which has been modified, by the way, after the first call to strtok().