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STRTOK
Section: Linux Programmer's Manual (3)
Updated: 2000-02-13
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NAME
strtok, strtok_r - extract tokens from strings
SYNOPSIS
#include <string.h>
char *strtok(char *str, const char *delim);
char *strtok_r(char *str, const char *delim, char **saveptr);
DESCRIPTION
The strtok() function parses a string into a sequence of 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 should be NULL.
The delim argument specifies a set of characters 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 character.
If no more tokens are found, strtok() returns NULL.
A sequence of two or more contiguous delimiter characters in
the parsed string is considered to be a single delimiter.
Delimiter characters at the start or end of the string are ignored.
Put another way: the tokens returned by strtok()
are always non-empty strings.
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.
EXAMPLE
The following program 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 character(s)
to be used to separate that string into "major" tokens.
The third argument specifies the delimiter character(s)
to be used to separate the "major" tokens into subtokens.
#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, j, token);
for (str2 = token; ; str2 = NULL) {
subtoken = strtok_r(str2, argv[3], &saveptr2);
if (subtoken == NULL)
break;
printf(" --> %s, subtoken);
}
}
exit(EXIT_SUCCESS);
} /* main */
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
BUGS
Avoid 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 character 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.
RETURN VALUE
The strtok() and strtok_r() functions return a pointer to
the next token, or NULL if there are no more tokens.
CONFORMING TO
- strtok()
-
SVr4, POSIX.1-2001, 4.3BSD, C89.
- strtok_r()
-
POSIX.1-2001
SEE ALSO
index(3),
memchr(3),
rindex(3),
strchr(3),
strpbrk(3),
strsep(3),
strspn(3),
strstr(3),
wcstok(3)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- EXAMPLE
-
- BUGS
-
- RETURN VALUE
-
- CONFORMING TO
-
- SEE ALSO
-
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