memccpy ( )【C語言庫函數原始碼】

【C語言庫函數原始碼】

【本程式在Dev C++ 4.9.9.2 下編譯通過】

#include <stdlib.h>

/*

   Copies bytes from src to dest until count bytes have been  copied,or up to and including the character c, whichever comes first.

   如果src前n個位元組中存在’c’，返回指向字元’c’後的第一個字元的指標；

否則返回NULL，src被複製。

*/

void * my_memccpy(void *dest,const void *src,int c,int count)

{

      while ( count && (*((char *)(dest = (char *)dest + 1) - 1) =

   *((char *)(src = (char *)src + 1) - 1)) != (char)c )

        count--;

   return(count ? dest : NULL);

}

/*這個函數的while條件判斷寫的比較長，看的眼疼，等價與以下寫法：*/

void * my_memccpy01(void *dst,const void *src,int c,int count)

{

   while (count)

   {

      *(char *)dst = *(char *)src;

      dst = (char *)dst + 1;

      if(*(char *)src == (char) c)

        break;

      src = (char *)src + 1;

      count--;

   }

   return(count ? dst : NULL);

}

int main()

{

   char a[12];

   char * p;

   char * str ="ammana_babi";

   char ch;

  

   ch =  '9';

   p = (char *)my_memccpy01(a,str,ch,strlen(str)+1);

   if(p == NULL)

      printf("/nCan't not find character. /n");

   else

   {

      printf("/nFind the character! /n");

      *p= '/0';

   }

   printf("/nThe String which has been copied is:/t");

   puts(a);

  

   printf("************************************");

 

   ch =  'b';

   p = (char *)my_memccpy01(a,str,ch,strlen(str)+1);

   if(p == NULL)

      printf("/nCan't not find character. /n");

   else

   {

      printf("/nFind the character! /n");

      *p = '/0';

   }

   printf("/nThe String which has been copied is:/t");

   puts(a);

  

   system("pause");

   return 0;

}