strtok的多线程实现
下面这段是vc库里strtok的源码，应该是实现了多线程的吧，但其中有些代码不明白，我在代码后做了标记
/***
*strtok.c - tokenize a string with given delimiters
*
* Copyright (c) 1989-1997, 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.
*
*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();*****************************作用？？？？？****************************
#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;******************************这里是怎样实现多线程的？
#else /* _MT */**********************************************************************************
str = nextoken;
#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;

/* Find the end of the token. If it is not the end of the string,
* put a null there. */
for ( ; *str ; str++ )
if ( map[*str >> 3] & (1 << (*str & 7)) ) {

*str++ = '\0';
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;
}


[解决办法]
不懂
线程安全的strtok_r()
[解决办法]
每个线程有自己专用的_tiddata内存块
当使用/MT编译时，不是使用静态变量nextoken来保存下一次查询的起点位置
而是使用线程自有的对象_tiddata里的_token来保存
这样不同线程同时调用就没有问题了