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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | BUGS | EXAMPLE | SEE ALSO | COLOPHON |
STRTOK(3) Linux Programmer's Manual STRTOK(3)
strtok, strtok_r - extract tokens from strings
#include <string.h>
char *strtok(char *str, const char *delim);
char *strtok_r(char *str, const char *delim, char **saveptr);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
strtok_r(): _POSIX_C_SOURCE
|| /* Glibc versions <= 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 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. In subsequent calls,
str should be NULL, and saveptr 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 │
└───────────┴───────────────┴───────────────────────┘
strtok()
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
strtok_r()
POSIX.1-2001, POSIX.1-2008.
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(" --> %s\n", subtoken);
}
}
exit(EXIT_SUCCESS);
}
Another example program using strtok() can be found in
getaddrinfo_a(3).
index(3), memchr(3), rindex(3), strchr(3), string(3), strpbrk(3),
strsep(3), strspn(3), strstr(3), wcstok(3)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2016-03-15 STRTOK(3)
Pages that refer to this page: index(3), strchr(3), string(3), strpbrk(3), strsep(3), strspn(3), strstr(3), wcstok(3), signal-safety(7)