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       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

       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 of 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 (but see NOTES).  In subsequent calls, str should be NULL,
       and saveptr (and the buffer that it points to) 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 attributes(7).

       │InterfaceAttributeValue                 │
       │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.


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


       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;

           if (argc != 4) {
               fprintf(stderr, "Usage: %s string delim subdelim\n",

           for (int 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)


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