遇到关于strtok的一个问题，郁闷了好一会儿终于找到答案

今天用这个函数用的郁闷了好一会儿，就是因为字符串是用的test2指针形式，而没有用test1那样的数组形式！

下面是我在网上看到的：

int main() {

char test1[] = "feng,ke,wei";

char *test2 = "feng,ke,wei";

char *p; p = strtok(test1, ",");

while(p)

{

printf("%s\n", p);

p = strtok(NULL, ",");

}

return 0;

}

运行结果:

feng

ke

wei

但如果用p = strtok(test2, ",")则会出现内存错误,这是为什么呢?是不是跟它里面那个静态变量有关呢? 我们来看看它的原码:

/***
*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.
*       //这里已经说得很详细了!!比MSDN都好! 
*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;                          //保存剩余子串的静态变量      
#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;                               //第一次调用函数所用到的原串

else
#ifdef _MT
                  str = ptd->_token;
#else  /* _MT */
                str = nextoken;                        //将函数第一参数设置为NULL时调用的余串

#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;                                    //此时的string返回余串的执行结果

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

//这里就是处理的核心了, 找到分隔符,并将其设置为'\0',当然'\0'也将保存在返回的串中
          for ( ; *str ; str++ )
                  if ( map[*str >> 3] & (1 << (*str & 7)) ) {
                        *str++ = '\0';                //这里就相当于修改了串的内容 ①
                          break;
                  }

/* Update nextoken (or the corresponding field in the per-thread data
           * structure */
#ifdef _MT
          ptd->_token = str;
#else  /* _MT */
        nextoken = str;                   //将余串保存在静态变量中,以便下次调用
#endif  /* _MT */

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