string - memmove源码

////  main.cpp//  AUTO_PRO////  Created by yanzhengqing on 12-12-11.//  Copyright (c) 2012年 yanzhengqing. All rights reserved.//#include #include using namespace std;/****memmove - Copy source buffer to destination buffer**Purpose:*       memmove() copies a source memory buffer to a destination memory buffer.*       This routine recognize overlapping buffers to avoid propogation.*       For cases where propogation is not a problem, memcpy() can be used.**Entry:*       void *dst = pointer to destination buffer*       const void *src = pointer to source buffer*       size_t count = number of bytes to copy**Exit:*       Returns a pointer to the destination buffer**Exceptions:*******************************************************************************///////////////////////////////////////////////////////////////////////////////////*说明：  1. __cdecl 是C Declaration的缩写（declaration，声明），表示C语言默认的函数调用方法：所有参数从右到左依次入栈，这些参数由调用者清除，称为手动清栈。被调用函数不会要求调用者传递多少参数，调用者传递过多或者过少的参数，甚至完全不同的参数都不会产生编译阶段的错误。  2.  将n字节长的内容从一个内存地址复制到另一个地址；与memcpy不同的是它可以正确作用于两个存在重叠的地址。  3.  按照ANSI(American National Standards Institute)标准，不能对void指针进行算法操作，即不能对void指针进行如p++的操作,所以需要转换为具体的类型指针来操作,例如char *。（引用网友的结论）  4.  size_t 类型定义在cstddef头文件中，该文件是C标准库的头文件stddef.h的C++版。它是一个与机器相关的unsigned类型，其大小足以保证存储内存中对象的大小。*/void * __cdecl smemmove (                       void * dst,                       constvoid * src,                       size_t count                        ){   void * ret = dst;#if defined (_M_MRX000) || defined (_M_ALPHA) || defined (_M_PPC)    {       externvoid RtlMoveMemory(void *,constvoid *, size_t count );        RtlMoveMemory( dst, src, count );    }#else  /* defined (_M_MRX000) || defined (_M_ALPHA) || defined (_M_PPC) */   if (dst <= src || (char *)dst >= ((char *)src + count)) {       /*         * Non-Overlapping Buffers  没有重叠         * copy from lower addresses to higher addresses         */       while (count--) {            *(char *)dst = *(char *)src;            dst = (char *)dst +1;            src = (char *)src +1;        }    }   else {       /*         * Overlapping Buffers    重叠了         * copy from higher addresses to lower addresses         */        dst = (char *)dst + count -1;        src = (char *)src + count -1;       while (count--) {            *(char *)dst = *(char *)src;            dst = (char *)dst -1;            src = (char *)src -1;        }    }#endif  /* defined (_M_MRX000) || defined (_M_ALPHA) || defined (_M_PPC) */   return(ret);}int main(){    constchar src[50] ="blog.csdn.net/barry_yan";    char dst[50]="you are a good boy and she is a good girl !!!!";   cout<endl;   smemmove(dst,src,strlen(src));   cout<endl;   return0;}/////////////////////////////////////////////////////////////////////////////////实验调试：you are a good boy and she is a good girl !!!!blog.csdn.net/barry_yanshe is a good girl !!!!