strtok

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  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
       pointer.

       The  strtok_r()  function  is  a  reentrant  version  of strtok().  The
       saveptr argument is a pointer to a char * variable that is used  inter-
       nally  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 (but see NOTES).  In sub-
       sequent calls, str should be NULL, and saveptr (and the buffer that  it
       points to) 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  to-
       ken, or NULL if there are no more tokens.

ATTRIBUTES
       For  an  explanation  of  the  terms  used  in  this  section,  see at-
       tributes(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.

NOTES
       On some implementations, *saveptr is required to be NULL on  the  first
       call to strtok_r() that is being used to parse str.

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 speci-
       fies the delimiter byte(s) to be used to separate that string into "ma-
       jor" 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\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(" --> %s\n", subtoken);
               }
           }

           exit(EXIT_SUCCESS);
       }

       Another   example  program  using  strtok()  can  be  found  in  getad-
       drinfo_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 5.05 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                               2019-10-10                         STRTOK(3)