strsep(3) Linux Man Page - System Grab Bag

Name

strsep - extract token from string

Library

Standard C library ( libc ", " -lc )

Synopsis

#include <string.h> 
char *strsep(char **restrict " stringp ", const char *restrict  delim );

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

strsep()

    Since glibc 2.19:
        _DEFAULT_SOURCE
    glibc 2.19 and earlier:
        _BSD_SOURCE

Description

If *stringp is NULL, the strsep() function returns NULL and does nothing else. Otherwise, this function finds the first token in the string *stringp that is delimited by one of the bytes in the string delim. This token is terminated by overwriting the delimiter with a null byte ('\e0'), and *stringp is updated to point past the token. In case no delimiter was found, the token is taken to be the entire string *stringp, and *stringp is made NULL.

Return Value

The strsep() function returns a pointer to the token, that is, it returns the original value of *stringp.

Attributes

For an explanation of the terms used in this section, see attributes(7). allbox; lbx lb lb T{ strsep()

Interface	Attribute	Value
T}	Thread safety	MT-Safe

Standards

None.

History

4.4BSD.

The strsep() function was introduced as a replacement for strtok(3), since the latter cannot handle empty fields. However, strtok(3) conforms to C89/C99 and hence is more portable.

Bugs

Be cautious when using this function. If you do use it, note that:

This function modifies its first argument.

This function cannot be used on constant strings.

The identity of the delimiting character is lost.

Examples

The program below is a port of the one found in strtok(3), which, however, doesn't discard multiple delimiters or empty tokens:

"$" " ./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/'" 1: a/bbb///cc
         --> a
         --> bbb
         -->
         -->
         --> cc
2: xxx
         --> xxx
3: yyy
         --> yyy
4:
         -->

Program Source

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

int
main(int argc, char *argv[])
{
    char *token, *subtoken;

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

    for (unsigned int j = 1; (token = strsep(&argv[1], argv[2])); j++) {
        printf("%u: %s\en", j, token);

        while ((subtoken = strsep(&token, argv[3])))
            printf("\et --> %s\en", subtoken);
    }

    exit(EXIT_SUCCESS);
}