Trusted answers to developer questions

Splitting a string using strtok() in C

Get Started With Data Science

Learn the fundamentals of Data Science with this free course. Future-proof your career by adding Data Science skills to your toolkit — or prepare to land a job in AI, Machine Learning, or Data Analysis.

In C, the strtok() function is used to split a string into a series of tokens based on a particular delimiter. A token is a substring extracted from the original string.

How strtok( ) works
How strtok( ) works

Syntax

The general syntax for the strtok() function is:

char *strtok(char *str, const char *delim)

Parameters

Let’s look at the parameters the strtok() function takes as input:

  • str: The string which is to be split
  • delim: The character on the basis of which the split will be done

Return value

The function performs one split and returns a pointer to the token split up. A null pointer is returned if the string cannot be split.

Example

Let’s start off by a simple example!

1. Extracting a single token

The following piece of code will just split up the Hello world string in two and will return the first token extracted from the function.

#include<stdio.h>
#include <string.h>
int main() {
char string[50] = "Hello world";
// Extract the first token
char * token = strtok(string, " ");
printf( " %s\n", token ); //printing the token
return 0;
}

2. Extracting all possible tokens

To find all possible splits of the string, based on a given delimiter, the function needs to be called in a loop. See the example below to see how this works.

Let’s see how we can split up a sentence on each occurrence of the white space character:

#include<stdio.h>
#include <string.h>
int main() {
char string[50] = "Hello! We are learning about strtok";
// Extract the first token
char * token = strtok(string, " ");
// loop through the string to extract all other tokens
while( token != NULL ) {
printf( " %s\n", token ); //printing each token
token = strtok(NULL, " ");
}
return 0;
}

Note: The strtok() function also modifies the original string. The original string is truncated to the first token.

#include<stdio.h>
#include <string.h>
int main() {
char string[50] = "Hello world";
printf( "Original string: %s\n", string ); //printing the string
// Extract the first token
char * token = strtok(string, " ");
printf( " %s\n", token ); //printing the token
printf( "String after strtok(): %s\n", string ); //printing the string
return 0;
}

Characteristics and limitations of strtok()

  • The input string is modified by replacing the delimiter with null characters. This is not a good thing when we want to preserve the original string.

  • It is not thread-safeThread-safe means that a piece of code or function can be safely used by multiple threads concurrently without causing unexpected behavior or data corruption..

  • We use strtok() in a loop in order to extract all tokens from a string.

Test your knowledge !

1

What does the strtok() function do in C?

A)

Concatenates two strings

B)

Searches for a substring within a string

C)

Splits a string into smaller tokens based on a delimiter

D)

Copies a string into another string

Question 1 of 30 attempted

RELATED TAGS

c
string split
strtok
Copyright ©2024 Educative, Inc. All rights reserved
Did you find this helpful?