c++ - 为什么在函数内部初始化时 C++ 对象会被破坏？我能做些什么来防止它？

Question

在这里，当我插入堆栈时，为什么对象会被销毁？

#include <iostream>
#include <stack>

class One
{
private:
        int i;
public:
        One(int i) {this->i = i;}
        ~One() {std::cout << "value " << this->i << " is destroyed\n";}
};

int main()
{
        std::stack<One> stack;
        stack.push(One(1));
        stack.push(One(2));

        std::cout << "Now I'll stop\n";
}

我预计在 Now I'll stop 之前看不到任何输出.但我明白了

value 1 is destroyed
value 2 is destroyed
Now I'll stop
value 1 is destroyed
value 2 is destroyed

如果我想防止它们被破坏，我该怎么办？

Answer 1

One(1)和 One(2)构造两个临时对象，传递给 push然后复制(移动)到 stack .临时表在完整表达式后立即销毁。
如果你想避免构建临时文件，你可以使用 emplace 反而。

Pushes a new element on top of the stack. The element is constructed in-place, i.e. no copy or move operations are performed.

例如。

stack.emplace(1);
stack.emplace(2);