strtok(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

STRTOK(3P)              POSIX Programmer's Manual             STRTOK(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       strtok, strtok_r — split string into tokens

SYNOPSIS         top

       #include <string.h>

       char *strtok(char *restrict s, const char *restrict sep);
       char *strtok_r(char *restrict s, const char *restrict sep,
           char **restrict state);

DESCRIPTION         top

       For strtok(): The functionality described on this reference page
       is aligned with the ISO C standard. Any conflict between the
       requirements described here and the ISO C standard is
       unintentional. This volume of POSIX.1‐2017 defers to the ISO C
       standard.

       A sequence of calls to strtok() breaks the string pointed to by s
       into a sequence of tokens, each of which is delimited by a byte
       from the string pointed to by sep.  The first call in the
       sequence has s as its first argument, and is followed by calls
       with a null pointer as their first argument. The separator string
       pointed to by sep may be different from call to call.

       The first call in the sequence searches the string pointed to by
       s for the first byte that is not contained in the current
       separator string pointed to by sep.  If no such byte is found,
       then there are no tokens in the string pointed to by s and
       strtok() shall return a null pointer. If such a byte is found, it
       is the start of the first token.

       The strtok() function then searches from there for a byte that is
       contained in the current separator string. If no such byte is
       found, the current token extends to the end of the string pointed
       to by s, and subsequent searches for a token shall return a null
       pointer. If such a byte is found, it is overwritten by a NUL
       character, which terminates the current token. The strtok()
       function saves a pointer to the following byte, from which the
       next search for a token shall start.

       Each subsequent call, with a null pointer as the value of the
       first argument, starts searching from the saved pointer and
       behaves as described above.

       The implementation shall behave as if no function defined in this
       volume of POSIX.1‐2017 calls strtok().

       The strtok() function need not be thread-safe.

       The strtok_r() function shall be equivalent to strtok(), except
       that strtok_r() shall be thread-safe and the argument state
       points to a user-provided pointer that allows strtok_r() to
       maintain state between calls which scan the same string. The
       application shall ensure that the pointer pointed to by state is
       unique for each string (s) being processed concurrently by
       strtok_r() calls. The application need not initialize the pointer
       pointed to by state to any particular value. The implementation
       shall not update the pointer pointed to by state to point
       (directly or indirectly) to resources, other than within the
       string s, that need to be freed or released by the caller.

RETURN VALUE         top

       Upon successful completion, strtok() shall return a pointer to
       the first byte of a token. Otherwise, if there is no token,
       strtok() shall return a null pointer.

       The strtok_r() function shall return a pointer to the token
       found, or a null pointer when no token is found.

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

   Searching for Word Separators
       The following example searches for tokens separated by <space>
       characters.

           #include <string.h>
           ...
           char *token;
           char line[] = "LINE TO BE SEPARATED";
           char *search = " ";

           /* Token will point to "LINE". */
           token = strtok(line, search);

           /* Token will point to "TO". */
           token = strtok(NULL, search);

   Find First two Fields in a Buffer
       The following example uses strtok() to find two character strings
       (a key and data associated with that key) separated by any
       combination of <space>, <tab>, or <newline> characters at the
       start of the array of characters pointed to by buffer.

           #include <string.h>
           ...
           char    *buffer;
           ...
           struct element {
               char *key;
               char *data;
           } e;
           ...
           // Load the buffer...
           ...
           // Get the key and its data...
           e.key = strtok(buffer, " \t\n");
           e.data = strtok(NULL, " \t\n");
           // Process the rest of the contents of the buffer...
           ...

APPLICATION USAGE         top

       Note that if sep is the empty string, strtok() and strtok_r()
       return a pointer to the remainder of the string being tokenized.

       The strtok_r() function is thread-safe and stores its state in a
       user-supplied buffer instead of possibly using a static data area
       that may be overwritten by an unrelated call from another thread.

RATIONALE         top

       The strtok() function searches for a separator string within a
       larger string. It returns a pointer to the last substring between
       separator strings.  This function uses static storage to keep
       track of the current string position between calls. The new
       function, strtok_r(), takes an additional argument, state, to
       keep track of the current position in the string.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       The Base Definitions volume of POSIX.1‐2017, string.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                        STRTOK(3P)

Pages that refer to this page: string.h(0p)localeconv(3p)