c++ - 什么时候创建本地静态对象？

Question

C++ Primer 一书的第 6.1.1 章说:

Each local static object is initialized before the first time execution passes through the object’s definition. Local statics are not destroyed when a function ends; they are destroyed when the program terminates.

为了检查这一点，我运行了以下代码:

#include <iostream>

using std::clog;
using std::endl;

struct Bar {
    Bar() {
        clog << "constructing Num object" << endl;
    }

    int i = 0,
        j = 0;

    ~Bar() {
        clog << "destructing Num object" << endl;
    }
};

void foo() {
    clog << "foo() started" << endl;
    static Bar b;
    return;
}

int main() {
    if (true) {
        clog << "if-statement started" << endl;
        foo();
    }

    clog << "if-statement exited" << endl;

    return 0;
}

在本书的这一点上，我还没有介绍 structs 和 classes，但我的理解是函数 Bar() 在创建时将一条消息记录到标准输出，并且 b 被默认初始化。如果是这样，那为什么输出显示对象在控制到达static Bar b;时被构造/初始化，而不是在到达这条语句之前？

输出:

if-statement started
foo() started
constructing Num object
if-statement exited
destructing Num object

Answer 1

When are local static objects created?

正如你的书所说:“在第一次执行通过对象的定义之前”。

更准确地说，标准的措辞是:

Dynamic initialization of a block-scope variable with static storage duration or thread storage duration is performed the first time control passes through its declaration; such a variable is considered initialized upon the completion of its initialization.

我认为你对“之前”这个词太执着了。 🙂