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

   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

   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

   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

   Interface   Attribute      Value                 
   strtok()    Thread safety  MT-Unsafe race:strtok 
   strtok_r()  Thread safety  MT-Safe               


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

          POSIX.1-2001, POSIX.1-2008.


   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


   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 4.09 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


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.