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() 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 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
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 function int 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:
strtok() | strtok_r() |
It is used to break string str into a series of tokens | It is used to decode a string into a pattern for tokens. |
The syntax is as follows: char *strtok(char *str, const char *delim) | Its syntax is as follows: char *strtok_r(char *string, const char *limiter, char **context); |
It uses the delimiter to proceed. | It is a re-entered variant of strtok(). |
It takes two parameters. | It takes three parameters. |
Its return value is a pointer to the first token found in the string | It is defined in header file <string.h> |
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