strcpy&memcpy&memmove

strcpy

extern char *strcpy(char *dest,char *source);
{
    assert((dest!=NULL)&&(source!=NULL));

    char *address=dest;
    while((*dest++=*source++)!='\0');

    return address;
}

　　把source所指由NULL结束的字符串复制到dest所指的数组中。source和dest所指内存区域不可以重叠且dest必须有足够的空间来容纳source的字符串。返回指向dest的指针。

memcpy

void *memcpy(void *dest, const void *source, size_t count)//没有对内存重叠进行检查
{
    assert((dest!=NULL)&&(source!=NULL));

    char* tmpDest=(char*)dest;
    char* tmpSource=(const char*)source;
    while(count--)
        *tmpDest++=*tmpSource++;
    return tmpDest;
}

memmove

　　Copies the values of num bytes from the location pointed by source to the memory block pointed by destination. Copying takes place as if an intermediate buffer were used, allowing the destination and source to overlap

void* memmove(void* dest,const void* src,size_t num)
{
    assert((dest!=NULL)&&(src!=NULL));

    char* tmpDest=(char*)dest;
    char* tmpSrc=(const char*)src;

    if(src>dest||src+num<dest)
    {
        while(num--)
            *tmpDest++=*tmpSrc++;
    }
    else
    {
        tmpDest=dest+num-;
        tmpSrc=src+num-;
        while(num--)
            *tmpDest--=*tmpSrc--;
    }
    return dest;
}