memmove（）与memcpy（）的区别与实现

equalsnull



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// MemMove.cpp : 定义控制台应用程序的入口点。

//

#include "stdafx.h"

#include <iostream>

using namespace std;

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void* memmove(void* dest, const void* src, size_t n)

{

if (n <= 0)

{

cout << "Invalid count number." << endl;

}

if (dest == NULL || src == NULL)

{

cout << "The dest or src address is null." << endl;

}

if (dest == src)

{

cout << "The dest equals src." << endl;

}

if ((char*)dest <= (char*)src || (char*)dest >= (char*)src + n)

{//对应图中2,3,4三种情况，赋值过程中，src中未使用的不会被覆盖

char* de = (char*)dest;

const char* sr = (const char*)src;

while (n--)

{

*de++ = *sr++;

}

}

else

{//对应图中的第一种情况

char* de = (char*)dest + n -1;

const char* sr = (const char*)src + n - 1;

while (n--)

{

*de-- = *sr--;

}

}

return dest;

}

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void* memmcpy(void* dest, const void* src, size_t n)

{

if (n <= 0)

{

cout << "Invalid count number." << endl;

}

if (dest == NULL || src == NULL)

{

cout << "The dest or src address is null." << endl;

}

if (dest == src)

{

cout << "The dest equals src." << endl;

}

char* de = (char*)dest;

const char* sr = (const char*)src;

while (n--)

{

*de++ = *sr++;

}

return dest;

}

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int _tmain(int argc, _TCHAR* argv[])

{

char* p = "hello,world";

char dest[12] = {0};

char *q = (char*)memmove(dest,p,5);

cout << dest << endl;

cout << q << endl;

return 0;

}