内存拷贝实现

void* _memove(void* dest,const void*src,size_t count)
{
    assert((dest != NULL) && (src != NULL));
    assert(count>0);

    char* psrc = (char*)src;
    char* pdest = (char*)dest;

    //检查是否有重叠问题   
    if(pdest < psrc)
    {
        //正向拷贝   
        while(count--)
            *pdest++ = *psrc++;
    }
    else if(psrc < pdest)
    {
        //反向拷贝   
        psrc = psrc + count;
        pdest = pdest + count;
        while(count--)
            *pdest-- = *psrc--;
    }

    return dest;
}

void* _memcpy(void* dest,const void* src,size_t count)
{
    assert((dest != NULL) && (src != NULL));
    assert(count > 0);

    char* psrc = (char*)src;
    char* pdest = (char*)dest;
    while(count --)
        *pdest++ = *psrc++;

    return dest;
}