what does strtok(NULL, "\n") do?

Question

The C library function char *strtok(char *str, const char *delim) breaks string str into a series of tokens using the delimiter delim.

What happens when you put s = strtok(NULL, "\n")? what does it mean splitting null by \n?

Answer 1

It doesn't mean splitting NULL by \n.

If you pass a non-NULL value, you are asking it to start tokenizing the passed string.

If you pass a NULL value, you are asking to continue tokenizing the same string as before (usually used in loops).

Example:

int main(void)
{
   char *token, string[] = "a string, of,; ;;;,tokens";

   token = strtok(string, ", ;");
   do
   {
      printf("token: \"%s\"\n", token);
   }
   while (token = strtok(NULL, ", ;"));
}

Result:

token: "a"                                                                                                                                                   
token: "string"                                                                                                                                              
token: "of"                                                                                                                                                  
token: "tokens"