STRTOK(3)						     Linux Programmer's Manual							 STRTOK(3)

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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       strtok_r(): _POSIX_C_SOURCE
	   || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

       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 delim-
       iters 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  ('')
       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.

RETURN VALUE

       The strtok() and strtok_r() functions return a pointer to the next token, or NULL if there are no more tokens.

ATTRIBUTES

       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		   |
       +-----------+---------------+-----------------------+
CONFORMING TO

       strtok()
	      POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

       strtok_r()
	      POSIX.1-2001, POSIX.1-2008.

BUGS

       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.

EXAMPLE

       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
",
		       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);
       }

       Another example program using strtok() can be found in getaddrinfo_a(3).

SEE ALSO

       index(3), memchr(3), rindex(3), strchr(3), string(3), strpbrk(3), strsep(3), strspn(3), strstr(3), wcstok(3)

COLOPHON

       This page is part of release 4.15 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
								    2017-09-15								 STRTOK(3)