C++中关于strtok()函数的用法

strtok:
#include <string.h>
char *strtok(char *str, const char *delim);
char *strtok_r(char *str, const char *delim, char **saveptr);
功能：分解字符串为一组标记串。str为要分解的字符串，delim为分隔符字符串。
说明：首次调用时，str必须指向要分解的字符串，随后调用要把s设成NULL。
     strtok在str中查找包含在delim中的字符并用NULL('/0')来替换，直到找遍整个字符串。
     返回指向下一个标记串。当没有标记串时则返回空字符NULL。
实例：用strtok来判断ip地址是否合法：ip_strtok.c：
[c-sharp] view plaincopy
//ip_strtok.c  
#include <stdio.h>  
#include <string.h>  
int main(int argc, char **argv)  
{  
  char temp_buf[100] = {};  
  char p_temp[100];  
  char *p=NULL;  
  char *t = ".";  
  int m,n,i;  
  int j=0,s=0;  
   
  if(argc!=2)  
  {  
    printf("param must 2/n");  
    return -1;  
  }  
  strcpy(temp_buf, argv[1]);  
  for(i=0; i<strlen(temp_buf);i++)  
  {  
    if(temp_buf[i] == *t)j++;  
    if(temp_buf[i] == *t && (temp_buf[i+1]>='0'&&temp_buf[i+1]<='9'))  
    {  
      s++;  
    }  
  }  
  if(j!=3 || j!=s)  
  {  
    printf("ip param format error/n");  
    return -1;  
  }  
  p = strtok(temp_buf, t);  
   
  while(p!=NULL)  
  {  
     strcpy(p_temp, p);  
     printf("%s /n", p_temp);  
     for(n=0; n<strlen(p_temp);n++)  
     {  
       if(!(p_temp[n]>='0'&&p_temp[n]<='9'))  
       {  
         printf("ip param error/n");  
         return -1;  
       }  
     }  
       
     m = atoi(p_temp);  
     if(m>255)  
     {  
       printf("ip invalid /n");  
       return -1;  
     }  
       
     p=strtok(NULL, ".");  
     printf("p = %s/n",p);  
  }  
  printf("ok! ip correct! ip=%s/n", argv[1]);  
  return 0;  
}  
编译运行：
[root@localhost liuxltest]# uname -r
2.6.26  
[root@localhost liuxltest]# gcc -Wall ip_strtok.c -o ip_strtok
[root@localhost liuxltest]# ./ip_strtok 172.18.4.255
172
p = 18
18
p = 4
4
p = 255
255
p = (null)
ok! ip correct! ip=172.18.4.255
[root@localhost liuxltest]# ./ip_strtok 172.18.
ip param format error
strtok实现函数：
xl_strtok.c
[c-sharp] view plaincopy
#include <string.h>  
#include <stdio.h>  
#include <stdlib.h>  
char *xl_strtok(char *str, const char *delim);  
int main(int argc, char **argv)  
{        
   if(argc != 3)  
   {  
       printf("param must be 3 /n");  
       return -1;  
   }  
         
       char *temp;  
       char *p_temp;  
   char *p;  
   temp=(char *)malloc(100);  
   p_temp=(char *)malloc(100);  
   strcpy(temp, argv[1]);  
   strcpy(p_temp, argv[2]);  
   printf("temp = %s /n",temp);  
   printf("p_temp = %s /n", p_temp);  
       p = xl_strtok(temp, p_temp);  
       printf("%s/n", p);  
       return 0;  
}  
char *xl_strtok(char *s, const char *dm)  
{  
       static char *last;  
       char *tok;  
       if(s == NULL)  
               s = last;  
       if(s == NULL)  
               return NULL;  
       tok = s;  
       while (*s != '/0')  
   {  
               while (*dm)  
       {  
                       if (*s == *dm)  
           {  
                               *s = '/0';  
                               last = s + 1;  
                               break;  
                       }  
                       s++;  
               }  
       }  
       return tok;  
}  
strtok源码：
/*********************************************************************/
/***
*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 _SECURE_VERSION
#include <internal.h>
#else  /* _SECURE_VERSION */
#include <mtdll.h>
#endif  /* _SECURE_VERSION */
/***
*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:
*
*******************************************************************************/
#ifdef _SECURE_VERSION
#define _TOKEN *context
#else  /* _SECURE_VERSION */
#define _TOKEN ptd->_token
#endif  /* _SECURE_VERSION */
#ifdef _SECURE_VERSION
char * __cdecl strtok_s (
       char * string,
       const char * control,
       char ** context
       )
#else  /* _SECURE_VERSION */
char * __cdecl strtok (
       char * string,
       const char * control
       )
#endif  /* _SECURE_VERSION */
{
       unsigned char *str;
       const unsigned char *ctrl = control;
       unsigned char map[32];
       int count;
#ifdef _SECURE_VERSION
       /* validation section */
       _VALIDATE_RETURN(context != NULL, EINVAL, NULL);
       _VALIDATE_RETURN(string != NULL || *context != NULL, EINVAL, NULL);
       _VALIDATE_RETURN(control != NULL, EINVAL, NULL);
       /* no static storage is needed for the secure version */
#else  /* _SECURE_VERSION */
       _ptiddata ptd = _getptd();
#endif  /* _SECURE_VERSION */
       /* 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
               str = _TOKEN;
       /* 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 */
       _TOKEN = str;
       /* Determine if a token has been found. */
       if ( string == str )
               return NULL;
       else
               return string;
}