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

17 Jun, 2022
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() 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.
char * strtok(char str[], const char *delims);
Example:
C
// C/C++ program for splitting a string// using strtok()#include& lt; stdio.h & gt;#include& lt; string.h & gt; 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 & quot;, 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() : 
CPP
// 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
Example 2 
C
// C code to demonstrate working of// strtok#include <stdio.h>#include <string.h> // Driver functionint 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
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 delimiters.
Example:
C
// C code to demonstrate practical application of// strtok#include <stdio.h>#include <string.h> // Driver functionint main(){    // Declaration of string    // Information to be converted into CSV file    char gfg[100] = " 1997 Ford E350 ac 3000.00";     // 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, ", tok);         // Use of strtok        // go through other tokens        tok = strtok(0, s);    }     return (0);}
Output: 
1997, Ford, E350, ac, 3000.00,
Let us see the differences in a tabular form as shown below as follows: 
The syntax is as follows:
char *strtok(char *str, const char *delim)
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