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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(): _SVID_SOURCE || _BSD_SOURCE || _POSIX_C_SOURCE >= 1 || _XOPEN_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

       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

       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.

   Multithreading (see pthreads(7))
       The strtok() function is not thread-safe.

       The strtok_r() function is thread-safe.

              SVr4, POSIX.1-2001, 4.3BSD, C89, C99.


       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>

       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",

           for (j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
               token = strtok_r(str1, argv[2], &saveptr1);
               if (token == NULL)
               printf("%d: %s\n", j, token);

               for (str2 = token; ; str2 = NULL) {
                   subtoken = strtok_r(str2, argv[3], &saveptr2);
                   if (subtoken == NULL)
                   printf(" --> %s\n", subtoken);


       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 3.74 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 http://www.kernel.org/doc/man-pages/.

GNU                                         2013-05-19                                  STRTOK(3)

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