显示这行错误 - 编程论坛

#2

rjsp2020-11-30 08:24

字符串赋值用 strcpy
数组赋值（包括字符数组）用 memcpy

#3

rjsp2020-11-30 08:28

程序代码：

#include <iostream>

struct box
{
    char maker[40];
    float height;
    float width;
    float length;
    float volume;
};

std::ostream& operator<<( std::ostream& os, const box& a )
{
    return os << a.maker  << '\n'
                << a.height << '\n'
                << a.width  << '\n'
                << a.length << '\n'
                << a.volume << '\n';
}

using namespace std;

int main( void )
{
    box a = { "asfdji", 2.3f, 5.6f, 4.7f, 7.8f };
    cout << a << endl;

    box b = a;
    cout << b << endl;
}

#4

hffjhhh2020-11-30 16:03

以下是引用rjsp在2020-11-30 08:28:35的发言：

#include <iostream>

struct box
{
    char maker[40];
    float height;
    float width;
    float length;
    float volume;
};

std::ostream& operator<<( std::ostream& os, const box& a )
{
    return os << a.maker  << '\n'
                << a.height << '\n'
                << a.width  << '\n'
                << a.length << '\n'
                << a.volume << '\n';
}

using namespace std;

int main( void )
{
    box a = { "asfdji", 2.3f, 5.6f, 4.7f, 7.8f };
    cout << a << endl;

    box b = a;
    cout << b << endl;
}

这个方法虽然可行，但是这一行看不懂：

std::ostream& operator<<( std::ostream& os, const box& a )

对于新手来说，我希望用更加基本的方法来做，修改如下：

程序代码：

#include<iostream>
using namespace std;
struct box{
    char maker[40];
    float height;
    float width;
    float length;
    float volume;
};
void function(box a){
    cout<<a.maker<<endl<<a.height<<endl<<a.width<<endl<<a.length<<endl<<a.volume<<endl<<endl;
}
box function1(box *a){
    box total;
    memcpy(total.maker,a->maker,8);
    total.height=a->height;
    total.width=a->width;
    total.length=a->length;
    total.volume=(a->height*a->width*a->length);
    return total;
}
int main(void){
    box aa={"asfdji",2.3,5.6,4.7,7.8};
    function(aa);
    box bb=function1(&aa);
    cout<<bb.maker<<endl<<bb.height<<endl<<bb.width<<endl<<bb.length<<endl<<bb.volume;
    return 0;
}

#5

rjsp2020-11-30 19:13

回复 4楼 hffjhhh

加上 #include <cstring>

再将 memcpy(total.maker,a->maker,8);
改为 memcpy(total.maker,a->maker,sizeof box::maker);

#6

hffjhhh2020-11-30 19:55

以下是引用rjsp在2020-11-30 19:13:25的发言：

加上 #include <cstring>

再将 memcpy(total.maker,a->maker,8);
改为 memcpy(total.maker,a->maker,sizeof box::maker);

发现将 memcpy(total.maker,a->maker,8)改为：

memcpy(total.maker,a->maker,sizeof box::maker);

或：

memcpy(total.maker,a->maker,sizeof(a->maker));

或：

memcpy(total.maker,a->maker,sizeof(total.maker));

编译器都没有报错,是不是这几种表示方法都可以？

[此贴子已经被作者于2020-11-30 21:46编辑过]

#7

rjsp2020-11-30 23:25

回复 6楼 hffjhhh

一样的，完全等价