strtok() and strtok_r() functions in C with examples (original) (raw)

Last Updated : 3 Jun, 2026

String splitting is the process of dividing a string into smaller parts based on a specified delimiter. In C, the strtok() and strtok_r() functions are commonly used to split strings into tokens.

• strtok() splits a string by a delimiter and returns one token at a time.
• strtok_r() is a reentrant version of strtok() that is safer for multithreaded programs.

strtok() Function

The strtok() method splits str[] according to given delimiters and returns the next token. It needs to be called in a loop to get all tokens. It returns NULL when there are no more tokens.

Syntax

char *strtok(char *str, const char *delims);

**Parameters:

• **str: It is the pointer to the string to be tokenized.
• **delims: It is a string containing all delimiters.

**Return Value:

• It returns the pointer to the first token encountered in the string.
• It returns NULL if there are no more tokens found.

**Example: C Program to demonstrate how to split a string using strtok().

C `

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

int main() { char str[] = "Geeks-for-Geeks";

// Returns first token
char* token = strtok(str, " - ");

// Keep printing tokens while one of the
// delimiters present in str[].
while (token != NULL) {
    printf(" % s\n", token);
    token = strtok(NULL, " - ");
}

return 0;

}

`

**Example: Program to demonstrates the use of the strtok() function to tokenize a string based on a delimiter.

C `

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

// Driver function int main() { // Declaration of string char gfg[100] = " Geeks - for - geeks - Contribute";

// Declaration of delimiter
const char s[4] = "-";
char* tok;

// Use of strtok
// get first token
tok = strtok(gfg, s);

// Checks for delimiter
while (tok != 0) {
    printf(" %s\n", tok);

    // Use of strtok
    // go through other tokens
    tok = strtok(0, s);
}

return (0);

}

`

Output

Geeks for geeks Contribute

strtok_r() Function

Just like strtok() function in C, strtok_r() does the same task of parsing a string into a sequence of tokens. strtok_r() is a reentrant version of strtok(), hence it is thread safe.

Syntax

char *strtok_r(char *str, const char *delim, char **saveptr);

**Parameters:

• **str: It is the pointer to the string to be tokenized.
• **delims: It is a string containing all delimiters.
• **saveptr: It is a pointer to a char * variable that is used internally by strtok_r() in order to maintain context between successive calls that parse the same string.

**Return Value:

• It returns the pointer to the first token encountered in the string.
• It returns NULL if there are no more tokens found.

**Example: a Simple C program to show the use of strtok_r().

C `

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

int main() { char str[] = "Geeks for Geeks"; char* token; char* rest = str;

while ((token = strtok_r(rest, " ", &rest)))
    printf("%s\n", token);

return (0);

}

`

**Output

Geeks for Geeks

**Example: The below C program demonstrates the use of strtok_r() function for Nested Tokenization.

C `

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

int main() { char str[] = "Hello, World! Geeks for Geeks."; const char outer_delimiters[] = "!."; const char inner_delimiters[] = " ,";

char* token;
char* outer_saveptr = NULL;
char* inner_saveptr = NULL;

token = strtok_r(str, outer_delimiters, &outer_saveptr);

while (token != NULL) {
    printf("Outer Token: %s\n", token);

    char* inner_token = strtok_r(
        token, inner_delimiters, &inner_saveptr);

    while (inner_token != NULL) {
        printf("Inner Token: %s\n", inner_token);
        inner_token = strtok_r(NULL, inner_delimiters,
                               &inner_saveptr);
    }

    token = strtok_r(NULL, outer_delimiters,
                     &outer_saveptr);
}

return 0;

}

`

**Output

Outer Token: Hello, World Inner Token: Hello Inner Token: World Outer Token: Geeks for Geeks Inner Token: Geeks Inner Token: for Inner Token: Geeks

Difference Between strtok() and strtok_r()

Let us see the differences between strtok() and strtok_r() functions in a tabular form as shown below: