C++拷贝、赋值与销毁

copy

当用一个类的变量去初始化一个类的时候，会复制出该类的一个副本，而不是淡出的引用，即，改变新的变量，原来的变量不会改变。

用构造函数或者赋值均会复制出该类的一个副本。

代码

#include<iostream>
#include<exception>
#include<fstream>
#include<sstream>
#include<string>
#include<vector>
#include<iterator>
#include<list>
#include<deque>
#include<stack>
#include<queue>
#include<concurrent_priority_queue.h>
#include<algorithm>
#include<numeric>
#include<functional>  //bind
#include<map>
#include<set>
#include<unordered_map>
#include<memory>
using namespace std;

class TestCopy
{
public:
int num[10];
string str;

TestCopy(int n, string s)
{
num[0] = n;
str = s;
}
};

int main()
{
cout << "start!" << endl;

TestCopy tc1(1, "233");
TestCopy tc2(tc1);

tc2.num[0] = 3;
tc2.str = "after-change";

cout << "test copy 1 : " << tc1.num[0] << ", " << tc1.str << endl;
cout << "test copy 2 : " << tc2.num[0] << ", " << tc2.str << endl;

TestCopy tc3 = tc1;
tc3.num[0] = 100;

cout << "test copy 1 : " << tc1.num[0] << ", " << tc1.str << endl;
cout << "test copy 3 : " << tc3.num[0] << ", " << tc3.str << endl;

cout << "end!" << endl;
system("pause");
return EXIT_SUCCESS;
}

上面的代码中，

tc1

复制后生成了

tc2

，修改

tc2

，

tc1

不发生改变。修改

tc3

，

tc1

也不发生改变。

左值和右值

返回值是引用类型，且没有被

const

修饰时，可以将其返回值作为左值

代码

#include<iostream>
#include<exception>
#include<fstream>
#include<sstream>
#include<string>
#include<vector>
#include<iterator>
#include<list>
#include<deque>
#include<stack>
#include<queue>
#include<concurrent_priority_queue.h>
#include<algorithm>
#include<numeric>
#include<functional>  //bind
#include<map>
#include<set>
#include<unordered_map>
#include<memory>
#include<assert.h>
using namespace std;

char &lV(string &a, int idx)
{
assert((!a.empty()) && a.length() > idx);
return a[idx];
}

int main()
{
cout << "start!" << endl;

string s("ABCDEF");
cout << s << endl;

lV(s, 0) = 'Z';
cout << s << endl;

cout << "end!" << endl;
system("pause");
return EXIT_SUCCESS;
}

参考链接:http://blog.csdn.net/sunshinewave/article/details/7830701