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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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strtok(3) Library Functions Manual strtok(3)
strtok, strtok_r - extract tokens from strings
Standard C library (libc, -lc)
#include <string.h>
char *strtok(char *_Nullable restrict str, const char *restrict delim);
char *strtok_r(char *_Nullable restrict str, const char *restrict delim,
char **restrict saveptr);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
strtok_r():
_POSIX_C_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
The strtok() function breaks a string into a sequence of zero or
more nonempty 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 must be NULL.
The delim argument specifies a set of bytes 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 byte. If no more tokens are found, strtok()
returns NULL.
A sequence of calls to strtok() that operate on the same string
maintains a pointer that determines the point from which to start
searching for the next token. The first call to strtok() sets
this pointer to point to the first byte of the string. The start
of the next token is determined by scanning forward for the next
nondelimiter byte in str. If such a byte is found, it is taken as
the start of the next token. If no such byte is found, then there
are no more tokens, and strtok() returns NULL. (A string that is
empty or that contains only delimiters will thus cause strtok() to
return NULL on the first call.)
The end of each token is found by scanning forward until either
the next delimiter byte is found or until the terminating null
byte ('\0') is encountered. If a delimiter byte is found, it is
overwritten with a null byte to terminate the current token, and
strtok() saves a pointer to the following byte; that pointer will
be used as the starting point when searching for the next token.
In this case, strtok() returns a pointer to the start of the found
token.
From the above description, it follows that a sequence of two or
more contiguous delimiter bytes in the parsed string is considered
to be a single delimiter, and that delimiter bytes at the start or
end of the string are ignored. Put another way: the tokens
returned by strtok() are always nonempty strings. Thus, for
example, given the string "aaa;;bbb,", successive calls to
strtok() that specify the delimiter string ";," would return the
strings "aaa" and "bbb", and then a null pointer.
The strtok_r() function is a reentrant version of 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 (but see
VERSIONS). In subsequent calls, str should be NULL, and saveptr
(and the buffer that it points to) 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.
The strtok() and strtok_r() functions return a pointer to the next
token, or NULL if there are no more tokens.
For an explanation of the terms used in this section, see
attributes(7).
┌────────────────────────┬───────────────┬───────────────────────┐
│ Interface │ Attribute │ Value │
├────────────────────────┼───────────────┼───────────────────────┤
│ strtok() │ Thread safety │ MT-Unsafe race:strtok │
├────────────────────────┼───────────────┼───────────────────────┤
│ strtok_r() │ Thread safety │ MT-Safe │
└────────────────────────┴───────────────┴───────────────────────┘
On some implementations, *saveptr is required to be NULL on the
first call to strtok_r() that is being used to parse str.
strtok()
C11, POSIX.1-2008.
strtok_r()
POSIX.1-2008.
strtok()
POSIX.1-2001, C89, SVr4, 4.3BSD.
strtok_r()
POSIX.1-2001.
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 byte 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.
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 byte(s) to be used to
separate that string into "major" tokens. The third argument
specifies the delimiter byte(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("\t --> %s\n", subtoken);
}
}
exit(EXIT_SUCCESS);
}
Another example program using strtok() can be found in
getaddrinfo_a(3).
memchr(3), strchr(3), string(3), strpbrk(3), strsep(3), strspn(3),
strstr(3), wcstok(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 strtok(3)
Pages that refer to this page: strchr(3), string(3), strpbrk(3), strsep(3), strspn(3), strstr(3), wcstok(3), signal-safety(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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