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strtok.3

STRTOK

Section: Linux Programmer's Manual (3)
Updated: 2008-10-29
Index Return to Main Contents
 

NAME

strtok, strtok_r - extract tokens from strings  

SYNOPSIS

#include <string.h>

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

char *strtok_r(char *str, const char *delim, char **saveptr);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

strtok_r(): _SVID_SOURCE || _BSD_SOURCE || _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE  

DESCRIPTION

The strtok() function parses a string into a sequence of tokens. On the first call to strtok() the string to be parsed should be specified in str. In each subsequent call that should parse the same string, str should be NULL.

The delim argument specifies a set of characters that delimit the tokens in the parsed string. The caller may specify different strings in delim in successive calls that parse the same string.

Each call to strtok() returns a pointer to a null-terminated string containing the next token. This string does not include the delimiting character. If no more tokens are found, strtok() returns NULL.

A sequence of two or more contiguous delimiter characters in the parsed string is considered to be a single delimiter. Delimiter characters at the start or end of the string are ignored. Put another way: the tokens returned by strtok() are always non-empty strings.

The strtok_r() function is a reentrant version strtok(). The saveptr argument 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.

On the first call to strtok_r(), str should point to the string to be parsed, and the value of saveptr is ignored. In subsequent calls, str should be NULL, and saveptr should be unchanged since the previous call.

Different strings may be parsed concurrently using sequences of calls to strtok_r() that specify different saveptr arguments.  

RETURN VALUE

The strtok() and strtok_r() functions return a pointer to the next token, or NULL if there are no more tokens.  

CONFORMING TO

strtok()
SVr4, POSIX.1-2001, 4.3BSD, C89, C99.
strtok_r()
POSIX.1-2001.
 

BUGS

Be cautious when using these functions. If you do use them, note that:
*
These functions modify their first argument.
*
These functions cannot be used on constant strings.
*
The identity of the delimiting character is lost.
*
The strtok() function uses a static buffer while parsing, so it's not thread safe. Use strtok_r() if this matters to you.
 

EXAMPLE

The program below uses nested loops that employ strtok_r() to break a string into a two-level hierarchy of tokens. The first command-line argument specifies the string to be parsed. The second argument specifies the delimiter character(s) to be used to separate that string into "major" tokens. The third argument specifies the delimiter character(s) to be used to separate the "major" tokens into subtokens.

An example of the output produced by this program is the following:

$ ./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/'
1: a/bbb///cc
         --> a
         --> bbb
         --> cc
2: xxx
         --> xxx
3: yyy
         --> yyy
 

Program source

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int
main(int argc, char *argv[])
{
    char *str1, *str2, *token, *subtoken;
    char *saveptr1, *saveptr2;
    int j;

    if (argc != 4) {
        fprintf(stderr, "Usage: %s string delim subdelim\n",
                argv[0]);
        exit(EXIT_FAILURE);
    }

    for (j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
        token = strtok_r(str1, argv[2], &saveptr1);
        if (token == NULL)
            break;
        printf("%d: %s\n", j, token);

        for (str2 = token; ; str2 = NULL) {
            subtoken = strtok_r(str2, argv[3], &saveptr2);
            if (subtoken == NULL)
                break;
            printf("	 --> %s\n", subtoken);
        }
    }

    exit(EXIT_SUCCESS);
} /* main */
 

SEE ALSO

index(3), memchr(3), rindex(3), strchr(3), strpbrk(3), strsep(3), strspn(3), strstr(3), wcstok(3)  

COLOPHON

This page is part of release 3.21 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
CONFORMING TO
BUGS
EXAMPLE
Program source
SEE ALSO
COLOPHON

 

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