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) ; |
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.
The strtok
() and
strtok_r
() functions return a
pointer to the next token, or NULL if there are no more
tokens.
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. Usestrtok_r
() if this matters to you.
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\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); } /* 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
index(3), memchr(3), rindex(3), strchr(3), strpbrk(3), strsep(3), strspn(3), strstr(3), wcstok(3)
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