Q51327: INFO: strtok(): C Function – Documentation Supplement

Article: Q51327
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,2.0,4.0,5.0,6.0
Operating System(s): 
Keyword(s): kbcode kbCRT kbVC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
Last Modified: 25-JUL-2001

MS-DOS:5.1,6.0,6.00a,6.00ax,7.0; OS/2:5.1,6.0,6.00a; WINDOWS:1.0,1.5;
WINDOWS NT:1.0,2.0,4.0,5.0


-------------------------------------------------------------------------------
The information in this article applies to:

- The C Run-Time (CRT), used with:
   - Microsoft C for MS-DOS 
   - Microsoft C for OS/2 
   - Microsoft C/C++ for MS-DOS 
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5 
   - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0, 5.0, 6.0 
-------------------------------------------------------------------------------

SUMMARY
=======

In Microsoft C, the strtok() function takes two strings as arguments. The first
is a series of zero or more tokens separated by delimiters defined by the second
string. The first call to strtok() returns a pointer to the first token in the
first argument. To get the next token in the original string, a call to strtok()
must be made with NULL as the first argument, which tells strtok() to search for
the next token in the previous token string.

Keep the following information in mind when using strtok():

- strtok() will replace a delimiter in the original string with a NULL each
  time the function is called using the same string, so the original string is
  modified by the use of strtok().

- The second argument to strtok() can be changed at any time to a different
  delimiter.

- Only single characters are considered to be delimiters.

MORE INFORMATION
================

On the first call to strtok(), the function searches the string argument given
as the first parameter for any token delimiter defined in the second string
argument. Any further call to strtok() with NULL as the first argument will
return a pointer to the next token in the original string. The following sample
program from page 603 of the "Microsoft C Optimizing Compiler: Run-Time Library
Reference" manual for version 5.1 shows how strtok() searches a token string:

Sample Code
-----------

  /* Compile options needed: none
  */ 

  #include <string.h>
  #include <stdio.h>

  char string[] = "a string,of ,,tokens";
  char *token;

  void main(void)
  {
          token = strtok(string," ,"); /*There are two delimiters here*/ 
          while (token != NULL){
                  printf("The token is:  %s\n", token);
                  token = strtok(NULL," ,");
          }
  }

The output of this program is as follows:

- The token is: a

- The token is: string

- The token is: of

- The token is: tokens

The following is a sample representation of the area in memory around the token
pointer during execution of the above program. Note the replacement of the
delimiter with a NULL character each time a token is found:

  -------------------------------------------------------------
  |a |  |s |t |r |i |n |g |, |o |f |  |, |, |t |o |k |e |n |s |
  -------------------------------------------------------------
  This is the original string before the first call to strtok().

  -------------------------------------------------------------
  |a |\0|s |t |r |i |n |g |, |o |f |  |, |, |t |o |k |e |n |s |
  -------------------------------------------------------------
   ^----- Token will point here on the first call.

  -------------------------------------------------------------
  |a |\0|s |t |r |i |n |g |\0|o |f |  |, |, |t |o |k |e |n |s |
  -------------------------------------------------------------
         ^------ Token will point here on the second call.

  -------------------------------------------------------------
  |a |\0|s |t |r |i |n |g |\0|o |f |\0|, |, |t |o |k |e |n |s |
  -------------------------------------------------------------
                              ^----- Token will point here on
                                     the third call.

                               (and so on)

Additional query words:

======================================================================
Keywords          : kbcode kbCRT kbVC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : :1.0,1.5,2.0,4.0,5.0,6.0
Issue type        : kbinfo

=============================================================================

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