strtok

 

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Null-terminated byte strings

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Defined in header <string.h>
char *strtok( char          *str, const char          *delim );		(until C99)
char *strtok( char *restrict str, const char *restrict delim );		(since C99)

Finds the next token in a null-terminated byte string pointed to by str. The separator characters are identified by null-terminated byte string pointed to by delim.

This function is designed to be called multiples times to obtain successive tokens from the same string.

• If str != NULL, the call is treated as the first call to strtok for this particular string. The function searches for the first character which is not contained in delim.

• If no such character was found, there are no tokens in str at all, and the function returns a null pointer.
• If such character was found, it is the beginning of the token. The function then searches from that point on for the first character that is contained in delim.

• If no such character was found, str has only one token, and future calls to strtok will return a null pointer
• If such character was found, it is replaced by the null character '\0' and the pointer to the following character is stored in a static location for subsequent invocations.

• The function then returns the pointer to the beginning of the token

• If str == NULL, the call is treated as a subsequent calls to strtok: the function continues from where it left in previous invocation. The behavior is the same as if the previously stored pointer is passed as str.

Parameters

str	-	pointer to the null-terminated byte string to tokenize
delim	-	pointer to the null-terminated byte string identifying delimiters

Return value

Pointer to the beginning of the next token or NULL if there are no more tokens.

Note

This function is destructive: it writes the '\0' characters in the elements of the string str. In particular, a string literal cannot be used as the first argument of strtok.

Each call to this function modifies a static variable: is not thread safe.

Example

Run this code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
int main(void) 
{
    char *str = malloc(20);
    char *tok = NULL;
    int len = 0;
 
    strcpy(str, "This is a string");
    len = strlen(str);
 
    printf("string before strtok(): %s\n", str);
    tok = strtok(str, " ");
    while (tok) {
        printf("Token: %s\n", tok);
        tok = strtok(NULL, " ");
    }
 
    printf("Print mangled string after strtok()\n");
    for (int i = 0; i < len; i++) {
        if (str[i] == '\0') {
            printf("'\\0'");
        } else {
            printf("%c", str[i]);
        }
    }
    printf("\n");
    free(str);
 
    return 0;
}

Output:

string before strtok(): This is a string
Token: This
Token: is
Token: a
Token: string
Print mangled string after strtok()
This'\0'is'\0'a'\0'string

See also

C++ documentation for strtok