strncpy和memcpy

strcpy strncpy

memcpy

#include <string.h>

char *strncpy(char *restrict s1, const char *restrict s2, size_t n);

DESCRIPTION       

The  strncpy()  function shall copy not more than n bytes (bytes that follow a null byte are not copied) from the array pointed to by s2 to the array pointed to by s1.  If copying takes place between objects that overlap, the behavior is undefined.If the array pointed to by s2 is a string that is shorter than n bytes, null bytes shall be appended to the copy in the array pointed  to by s1, until n bytes in all are written.

RETURN VALUE       

The strncpy() function shall return s1; no return value is reserved to indicate an error.

#include<string.h>
int main(int agrn,char *agrc[])
{
        char dest[1024] = {0};
        char *src="Hello,Wrold";
        strncpy(dest,src,sizeof(dest)-1);
        dest[1024-1] = 0;
        return 0;
}

SYNOPSIS       #include <string.h>
void *memcpy(void *restrict s1, const void *restrict s2, size_t n);
DESCRIPTION       

The  memcpy()  function  shall copy n bytes from the object pointed to by s2 into the object pointed to by s1. If copying takes place between objects that overlap, the behavior is undefined.

RETURN VALUE       

The memcpy() function shall return s1; no return value is reserved to indicate an error.

#include<string.h>
#include<iostream>
using namespace std;
struct Object
{
        char name[255];
        void print()
        {
                cout<<"Name:"<<name;
        }
};
struct Test:public Object
{
        int id;
        short sex;
};
int main(int agrn,char*agrc[])
{
        Test obj1;
        strncpy(obj1.name,"Liuda",sizeof(obj1.name));
        obj1.name[sizeof(obj1.name)-1] = 0;
        obj1.id = 123;
        obj1.sex = 0;
        Test obj2;
        memcpy(&obj2,&obj1,sizeof(obj1));
        obj2.print();
        return 0;
}

在来说说他们的区别。

strncpy复制n个，但是，他毕竟是字符串函数，所以碰到\0，就不复制了。

memcpy就不是，他一定会复制n个字节的数据。