strtok, strtok_s

• If str is not a null pointer, 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 is a null pointer, the call is treated as a subsequent call 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

Return value

Returns pointer to the beginning of the next token or a null pointer 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 strtok modifies a static variable: is not thread safe.

Unlike most other tokenizers, the delimiters in strtok can be different for each subsequent token, and can even depend on the contents of the previous tokens.

The strtok_s function differs from the POSIX strtok_r function by guarding against storing outside of the string being tokenized, and by checking runtime constraints. The Microsoft CRT strtok_s signature matches this POSIX strtok_r definition, not the C11 strtok_s .

Example

#define __STDC_WANT_LIB_EXT1__ 1
#include <string.h>
#include <stdio.h>
 
int main(void)
{
    char input[] = "A bird came down the walk";
    printf("Parsing the input string '%s'\n", input);
    char *token = strtok(input, " ");
    while(token) {
        puts(token);
        token = strtok(NULL, " ");
    }
 
    printf("Contents of the input string now: '");
    for(size_t n = 0; n < sizeof input; ++n)
        input[n] ? putchar(input[n]) : fputs("\\0", stdout);
    puts("'");
 
#ifdef __STDC_LIB_EXT1__
    char str[] = "A bird came down the walk";
    rsize_t strmax = sizeof str;
    const char *delim = " ";
    char *next_token;
    printf("Parsing the input string '%s'\n", str);
    token = strtok_s(str, &strmax, delim, &next_token);
    while(token) {
        puts(token);
        token = strtok_s(NULL, &strmax, delim, &next_token);
    }
 
    printf("Contents of the input string now: '");
    for(size_t n = 0; n < sizeof str; ++n)
        str[n] ? putchar(str[n]) : fputs("\\0", stdout);
    puts("'");
#endif
}

Parsing the input string 'A bird came down the walk'
A
bird
came
down
the
walk
Contents of the input string now: 'A\0bird\0came\0down\0the\0walk\0'
Parsing the input string 'A bird came down the walk'
A
bird
came
down
the
walk
Contents of the input string now: 'A\0bird\0came\0down\0the\0walk\0'

References