.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 18:00:10 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Mon Jan 20 12:04:18 1997 by Andries Brouwer (aeb@cwi.nl)
.\" Modified Tue Jan 23 20:23:07 2001 by Andries Brouwer (aeb@cwi.nl)
.\"
.TH STRSEP 3  2021-03-22 "GNU" "Linux Programmer's Manual"
.SH NAME
strsep \- extract token from string
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <string.h>
.PP
.BI "char *strsep(char **restrict " stringp ", const char *restrict " delim );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR strsep ():
.nf
    Since glibc 2.19:
        _DEFAULT_SOURCE
    Glibc 2.19 and earlier:
        _BSD_SOURCE
.fi
.SH DESCRIPTION
If
.I *stringp
is NULL, the
.BR strsep ()
function returns NULL
and does nothing else.
Otherwise, this function finds the first token
in the string
.I *stringp
that is delimited by one of the bytes in the string
.IR delim .
This token is terminated by overwriting the delimiter
with a null byte (\(aq\e0\(aq),
and
.I *stringp
is updated to point past the token.
In case no delimiter was found, the token is taken to be
the entire string
.IR *stringp ,
and
.I *stringp
is made NULL.
.SH RETURN VALUE
The
.BR strsep ()
function returns a pointer to the token,
that is, it returns the original value of
.IR *stringp .
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR strsep ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
4.4BSD.
.SH NOTES
The
.BR strsep ()
function was introduced as a replacement for
.BR strtok (3),
since the latter cannot handle empty fields.
However,
.BR strtok (3)
conforms to C89/C99 and hence is more portable.
.SH BUGS
Be cautious when using this function.
If you do use it, note that:
.IP * 2
This function modifies its first argument.
.IP *
This function cannot be used on constant strings.
.IP *
The identity of the delimiting character is lost.
.SH EXAMPLES
The program below is a port of the one found in
.BR strtok (3),
which, however, doesn't discard multiple delimiters or empty tokens:
.PP
.in +4n
.EX
.RB "$" " ./a.out \(aqa/bbb///cc;xxx:yyy:\(aq \(aq:;\(aq \(aq/\(aq"
1: a/bbb///cc
         \-\-> a
         \-\-> bbb
         \-\->
         \-\->
         \-\-> cc
2: xxx
         \-\-> xxx
3: yyy
         \-\-> yyy
4:
         \-\->
.EE
.in
.SS Program source
\&
.EX
#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 (int j = 1; (token = strsep(&argv[1], argv[2])); j++) {
        printf("%d: %s\en", j, token);

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

    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR index (3),
.BR memchr (3),
.BR rindex (3),
.BR strchr (3),
.BR string (3),
.BR strpbrk (3),
.BR strspn (3),
.BR strstr (3),
.BR strtok (3)