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 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 NOTES). 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 |
- strtok()
- POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
- strtok_r()
- POSIX.1-2001, POSIX.1-2008.
On some implementations,
*saveptr is required to be NULL on the first
call to
strtok_r() that is being used to parse
str.
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
#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)