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

C provides two functions strtok() and strtok_r() for splitting a string by some delimiter. Splitting a string is a very common task. For example, we have a comma separated list of items from a file and we want individual items in an array.

strtok()

// Splits str[] according to given delimiters.
// and returns next token. It needs to be called
// in a loop to get all tokens. It returns NULL
// when there are no more tokens.
char * strtok(char str[], const char *delims);

// A C/C++ program for splitting a string 
// using strtok() 
#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; 
} 

Output:

Geeks
for
Geeks

strtok_r()
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()

There are two ways we can call strtok_r()

// The third argument saveptr 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.
char *strtok_r(char *str, const char *delim, char **saveptr);

Below is a simple C program to show the use of strtok_r() :

// C program to demonstrate working of strtok_r() 
// by splitting string based on space character. 
#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

Another Example of strtok :

// C code to demonstrate working of 
// strtok 
#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 delimeter 
    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

Practical Application
strtok can be used to split a string in multiple strings based on some separators. A simple CSV file support might be implemented using this function. CSV files have commas as delimeters.

// C code to demonstrate practical application of 
// strtok 
#include <stdio.h> 
#include <string.h> 
  
// Driver function 
int main() 
{ 
    // Declaration of string 
    // Information to be converted into CSV file 
    char gfg[100] = " 1997 Ford E350 ac 3000.00"; 
  
    // Declaration of delimeter 
    const char s[4] = " "; 
    char* tok; 
  
    // Use of strtok 
    // get first token 
    tok = strtok(gfg, s); 
  
    // Checks for delimeter 
    while (tok != 0) { 
        printf("%s, ", tok); 
  
        // Use of strtok 
        // go through other tokens 
        tok = strtok(0, s); 
    } 
  
    return (0); 
} 

Output:

1997, Ford, E350, ac, 3000.00,

Reference:
1) manual page strtok_r()
2) http://stackoverflow.com/questions/15961253/c-correct-usage-of-strtok-r

This article is contributed by MAZHAR IMAM KHAN and shantanu_23. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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