strtok()

/***
*strtok.c - tokenize a string with given delimiters
*
*         Copyright (c) Microsoft Corporation. All rights reserved.
*
*Purpose:
*         defines strtok() - breaks string into series of token
*         via repeated calls.
*
*******************************************************************************/

#include <cruntime.h>
#include <string.h>
#ifdef _MT
#include <mtdll.h>
#endif  /* _MT */

/***
*char *strtok(string, control) - tokenize string with delimiter in control
*
*Purpose:
*         strtok considers the string to consist of a sequence of zero or more
*         text tokens separated by spans of one or more control chars. the first
*         call, with string specified, returns a pointer to the first char of the
*         first token, and will write a null char into string immediately
*         following the returned token. subsequent calls with zero for the first
*         argument (string) will work thru the string until no tokens remain. the
*         control string may be different from call to call. when no tokens remain
*         in string a NULL pointer is returned. remember the control chars with a
*         bit map, one bit per ascii char. the null char is always a control char.
*       //          !! MSDN  ! 
*Entry:
*         char *string - string to tokenize, or NULL to get next token
*         char *control - string of characters to use as delimiters
*
*Exit:
*         returns pointer to first token in string, or if string
*         was NULL, to next token
*         returns NULL when no more tokens remain.
*
*Uses:
*
*Exceptions:
*
*******************************************************************************/

char * __cdecl strtok (
          char * string,
          const char * control
          )
{
          unsigned char *str;
          const unsigned char *ctrl = control;

          unsigned char map[32];
          int count;

#ifdef _MT
          _ptiddata ptd = _getptd();
#else  /* _MT */
          static char *nextoken;                       //                 
#endif  /* _MT */

          /* Clear control map */
          for (count = 0; count < 32; count++)
                  map[count] = 0;

          /* Set bits in delimiter table */
          do {
                  map[*ctrl >> 3] |= (1 << (*ctrl & 7));
          } while (*ctrl++);

          /* Initialize str. If string is NULL, set str to the saved
           * pointer (i.e., continue breaking tokens out of the string
           * from the last strtok call) */
          if (string)
                  str = string;                             //                       

else
#ifdef _MT
                  str = ptd->_token;
#else  /* _MT */
               str = nextoken;                      //          NULL      

#endif  /* _MT */

          /* Find beginning of token (skip over leading delimiters). Note that
           * there is no token iff this loop sets str to point to the terminal
           * null (*str == '\0') */
          while ( (map[*str >> 3] & (1 << (*str & 7))) && *str )
                  str++;

        string = str;                                  //   string          

          /* Find the end of the token. If it is not the end of the string,
           * put a null there. */

//          ,      ,      '\0',  '\0'          
          for ( ; *str ; str++ )
                  if ( map[*str >> 3] & (1 << (*str & 7)) ) {
                        *str++ = '\0';              //              ①
                          break;
                  }

          /* Update nextoken (or the corresponding field in the per-thread data
           * structure */
#ifdef _MT
          ptd->_token = str;
#else  /* _MT */
        nextoken = str;                 //           ,      
#endif  /* _MT */

          /* Determine if a token has been found. */
          if ( string == str )
                return NULL;
          else
                  return string;


1. strtok  

    ，strtok             （             “，。”）

            "\0".



  ，   =“，”    =“Fred，John，Ann”

  strtok     3     “Fred”      “John”       “Ann”    。

   C   

}