strsep(3) Library Functions Manual strsep(3)

strsep - extract token from string

Standard C library (libc, -lc)

#include <string.h>
char *strsep(char **restrict stringp, const char *restrict delim);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):


Since glibc 2.19:
glibc 2.19 and earlier:

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 ('\0'), 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.

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

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
strsep () Thread safety MT-Safe


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

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.

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:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
main(int argc, char *argv[])

char *token, *subtoken;
if (argc != 4) {
fprintf(stderr, "Usage: %s string delim subdelim\n", argv[0]);
for (unsigned int j = 1; (token = strsep(&argv[1], argv[2])); j++) {
printf("%u: %s\n", j, token);
while ((subtoken = strsep(&token, argv[3])))
printf("\t --> %s\n", subtoken);

memchr(3), strchr(3), string(3), strpbrk(3), strspn(3), strstr(3), strtok(3)

2023-02-05 Linux man-pages 6.03