C++:memset ,memcpy 和strcpy 的根本区别!

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <assert.h>

 

//memcpy：按字节复制

原型：extern void* memcpy(void *dest,void *src,unsigned int count)

//功能：由src所指内存区域复制count个字节到dest所指的内存区域；

//同strcpy

void *memcpy_su(void *dest, void *src, unsigned int count)

{

      

       assert ((dest!=NULL)&&(src!=NULL));

       char* bdest = (char*)dest;

       char* bsrc = (char*) src;

       while(count-->0)

        *bdest++ = *bsrc++;

       return dest;

}

 

 

 

//strcpy：复制字符串，遇到’\0’就结束

//原型：extern char *strcpy(char *dest,char *src)

//功能：把src所指由’\0’结束的字符串复制到dest所指的数组中；

//说明：src和dest所指内存区域是不可以重叠的且dest必须有足够的空间来容纳字符串。返回dest指针。

char *strcpy_su(char *dest,char *src)

{

       assert((dest!=NULL)&&(src!=NULL));

       char *address = dest;

       while((*dest++=*src++)!='\0')

              continue;

       return dest;

}

 

 

//memset：设置buffer所指的内存区域的前count个字节，用字符c来代替

//原型：extern void *memset(void *buffer,int c,int count);

 void *memset_su(void *buffer, int c, int count)

{

   assert ((buffer!=NULL));

   char* buffer2 = (char*)buffer;

   while(count-->0)

        *buffer2++ = c;

       return buffer;

}

 

 

 

 

void main()

{

       char str1[100]="abchjhgjghjgjgh";

       char str2[50]="efghdfkdjf";

      

       strcpy(str1, str2);

       printf("%s\n",str1);

 

 

       char a[3];

       memset(a, 'a', sizeof(a)-1);

       memset(&a[2], '\0',1);

       printf("%s\n",a);

 

      

       memcpy(str1, str2, strlen(str2));

       printf("%s\n",str1);

 

}