STRTOK(3) | Library Functions Manual | STRTOK(3)

# NAME

`strtok`, `strtok_r` — string token operations

# SYNOPSIS

`#include <string.h>`

char *
`strtok`(char *str, const char *sep);

char *
`strtok_r`(char *str, const char *sep, char **last);

# DESCRIPTION

This interface is obsoleted by strsep(3).

The `strtok`() function is used to isolate sequential tokens in a NUL-terminated string, str. These tokens are separated in the string by at least one of the characters in sep. The first time that `strtok`() is called, str should be specified; subsequent calls, wishing to obtain further tokens from the same string, should pass a null pointer instead. The separator string, sep, must be supplied each time, and may change between calls.

The `strtok_r`() function is a version of `strtok`() that takes an explicit context argument and is reentrant.

Since `strtok`() and `strtok_r`() modify the string, str should not point to an area in the initialized data segment.

# RETURN VALUES

The `strtok`() and `strtok_r`() functions return a pointer to the beginning of each subsequent token in the string, after replacing the separator character itself with a NUL character. When no more tokens remain, a null pointer is returned.

# EXAMPLES

The following will construct an array of pointers to each individual word in the string s:

    #define MAXTOKENS	128

    char s[512], *p, *tokens[MAXTOKENS];
    char *last;
    int i = 0;

    snprintf(s, sizeof(s), "cat dog horse cow");

    for ((p = strtok_r(s, " ", &last)); p;
        (p = strtok_r(NULL, " ", &last))) {
    	if (i < MAXTOKENS - 1)
    		tokens[i++] = p;
    }
    tokens[i] = NULL;

That is, `tokens[0]` will point to "cat", `tokens[1]` will point to "dog", `tokens[2]` will point to "horse", and `tokens[3]` will point to "cow".

# SEE ALSO

memchr(3), strchr(3), strcspn(3), strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3), wcstok(3)

# STANDARDS

The `strtok`() function conforms to ANSI X3.159-1989 (“ANSI C89”). The `strtok_r`() function conforms to IEEE Std 1003.1-2001 (“POSIX.1”).

# HISTORY

The `strtok`() function first appeared in AT&T System III UNIX and was reimplemented for 4.3BSD. The `strtok_r`() function first appeared in NetBSD 1.3 and was reimplemented for OpenBSD 2.7.

# BUGS

The System V `strtok`(), if handed a string containing only delimiter characters, will not alter the next starting point, so that a call to `strtok`() with a different (or empty) delimiter string may return a non-null value. Since this implementation always alters the next starting point, such a sequence of calls would always return `NULL`.

December 11, 2024 | Debian