C++ 销毁表达式中的临时对象 [英] C++ destruction of temporary object in an expression
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问题描述
给定以下代码:
#include <iostream>
struct implicit_t
{
implicit_t(int x) :
x_m(x)
{
std::cout << "ctor" << std::endl;
}
~implicit_t()
{
std::cout << "dtor" << std::endl;
}
int x_m;
};
std::ostream& operator<<(std::ostream& s, const implicit_t& x)
{
return s << x.x_m;
}
const implicit_t& f(const implicit_t& x)
{
return x;
}
int main()
{
std::cout << f(42) << std::endl;
return 0;
}
我得到以下输出:
ctor
42
dtor
虽然我知道这是正确的,但我不确定为什么.有stdc++知识的可以给我解释一下吗?
While I know this is correct, I'm not certain why. Is there anyone with stdc++ knowledge who can explain it to me?
推荐答案
临时对象被销毁作为评估完整表达式 (1.9) 的最后一步,该表达式(词法上)包含它们的创建点.[12.2/3]
Temporary objects are destroyed as the last step in evaluating the full-expression (1.9) that (lexically) contains the point where they were created. [12.2/3]
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