strcpy实现

Posted 2020-09-09

#include <bits/stdc++.h>
#include <iostream>
using namespace std; 



void* my_memcpy(void* dest,const void* src,unsigned int count)
{
    if (dest == NULL || src == NULL)
    {
        return NULL;
    } 
    void * ret = dest;
    if (dest <= src || ((char*) dest) >= ((char*)src + count))        // 低地址到高地址 
    {
        while (count--)
        {
            *(char*)dest = *(char*)src;
            dest = (char*)dest + 1;
            src = (char*)src + 1;
        }
    }
    else                                                             //高地址向低地址 
    {
        dest = (char*) dest + count -1;
        src  = (char*) src + count -1;
        while (count --)
        {
            *(char*)dest = *(char*)src;
            dest = (char*)dest - 1;
            src = (char*) src - 1;
        }
    }
    return ret;
}

char* my_strcpy(char* dest,const char* src)
{
    if (dest == NULL || src == NULL)
    {
        return NULL;
    }
    char* ret = dest;
    //没有考虑内存重叠情况 
    //while ((*dest++ = *src++) != ‘\0‘);
    my_memcpy(dest,src,strlen(src)+1);
    return ret;
}
int main()
{
    char str[10] = "abc";
    //my_strcpy(str+1,str);
    memcpy(str+1,str,sizeof(str)); 
    cout << str << endl;
}