关于strcpy的问题，解释一下为什么VS中标准的方法不用memcpy实现

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原文：http://blog.csdn.net/youyouzhishen/archive/2008/11/02/3207836.aspx

#include <cstring>

using namespace std;

inline char* myStrcpy(char* apszDest, char* apszSrc)

{

memcpy(apszDest, apszSrc, strlen(apszSrc) + 1);

return apszDest;

}

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

{

char lszSrc[] = "GOD, I'm a test string./n";

char lszDest[256];

printf("%s",myStrcpy(lszDest, lszSrc));

printf("%s",strcpy(lszDest, lszSrc));

return 0;

}

其实strcpy实现成我上面写的那样一样也可以实现strcpy,并且平均效率似乎要更高。这种错觉来自于debug时看到的strcpy的源代码（K&R中，一般的笔试题也广为通用此源代码）

其实到最近才知道，debug时可以看到strcpy的实现，memcpy一般情况下比strcpy那样的实现效率要高，这是很明显的，哪怕字符数量比较小，memcpy起码也不输给strcpy，但是，事实上，在优化后的release汇编代码就能发现，其实strcpy这样常用的函数（虽然是C Runtime Library的函数），但是编译器实际是做了优化的，这些叫做内部函数（中文版VS2005标准译法），直接就通过strcpy生成了汇编代码，所以实现上就没有必要使用memcpy了，见下面的汇编代码。

printf("%s",myStrcpy(lszDest, lszSrc));

00401026 8D 44 24 08 lea eax,[esp+8]

0040102A A4 movs byte ptr es:[edi],byte ptr [esi]

0040102B 8D 50 01 lea edx,[eax+1]

0040102E 8B FF mov edi,edi

00401030 8A 08 mov cl,byte ptr [eax]

00401032 83 C0 01 add eax,1

00401035 84 C9 test cl,cl

00401037 75 F7 jne wmain+30h (401030h)

00401039 2B C2 sub eax,edx

0040103B 83 C0 01 add eax,1

0040103E 50 push eax

0040103F 8D 44 24 0C lea eax,[esp+0Ch]

00401043 50 push eax

00401044 8D 4C 24 2C lea ecx,[esp+2Ch]

00401048 51 push ecx

00401049 E8 26 08 00 00 call memcpy (401874h)

0040104E 8B 35 A0 20 40 00 mov esi,dword ptr [__imp__printf (4020A0h)]

00401054 8D 54 24 30 lea edx,[esp+30h]

00401058 52 push edx

00401059 68 10 21 40 00 push offset string "%s" (402110h)

0040105E FF D6 call esi

00401060 83 C4 14 add esp,14h

printf("%s",strcpy(lszDest, lszSrc));

00401063 33 C0 xor eax,eax

00401065 8A 4C 04 08 mov cl,byte ptr [esp+eax+8]

00401069 88 4C 04 24 mov byte ptr [esp+eax+24h],cl

0040106D 83 C0 01 add eax,1

00401070 84 C9 test cl,cl

00401072 75 F1 jne wmain+65h (401065h)

00401074 8D 44 24 24 lea eax,[esp+24h]

00401078 50 push eax

00401079 68 10 21 40 00 push offset string "%s" (402110h)

0040107E FF D6 call esi

没有见过strcpy的汇编代码前。。。。哪想的到原来这么简单