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 ||

       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 main-
       tains 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 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  ('\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 speci-
       fies  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  getad-

       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 4.04 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

GNU                               2015-08-08                         STRTOK(3)
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