What is strtok_r() function in C language?

This function is similar to the strtok() function. The only key difference is that the _r, which is called as re-entrant function.

A re-entrant function is a function which can be interrupted during its execution. This type of function can be used to resume execution.

Because of this fact, re-entrant functions are thread-safe, means they can safely be interrupted by threads without any harm.

strtok_r() function has an extra parameter called the context. so that function can resume at the right place.

The syntax for strtok_r() function is as follows:

#include <string.h>
char *strtok_r(char *string, const char *limiter, char **context);

Example

Following is the C program for the use of strtok_r() function −

 Live Demo

#include <stdio.h>
#include <string.h>
int main(){
   char input_string[] = "Hello Tutorials Point";
   char token_list[20][20];
   char* context = NULL;
   char* token = strtok_r(input_string, " ", &context);
   int num_tokens = 0; // Index to token list. We will append to the list
   while (token != NULL){
      strcpy(token_list[num_tokens], token); // Copy to token list
      num_tokens++;
      token = strtok_r(NULL, " ", &context);
   }
   // Print the list of tokens
   printf("Token List:
");
   for (int i=0; i < num_tokens; i++) {
      printf("%s
", token_list[i]);
   }
   return 0;
}

Output

When the above program is executed, it produces the following result −

Token List:
Hello
Tutorials
Point