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 C89/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

#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)

2023-10-31 Linux man-pages 6.7