如果对象是在库中定义的，为什么静态创建的对象的构造函数不会在 main 函数之前执行？

问：

我正在尝试创建“插件”工厂。当用户请求创建对象工厂时，会查询其子工厂，并选择合适的子工厂来创建对象。

子库的实例是静态对象。创建后，它们将自己注册到顶级工厂。

以下是简化版本：

// ifactory.h
#ifndef _IFACTORY_H_
#define _IFACTORY_H_

#include <string>

class IFactory {
public:
    virtual int createNumber(const std::string& name, std::pair<int, int> range) = 0;

    virtual std::string getName() const = 0;

    virtual ~IFactory() = default;
};

#endif

// defaul_factory.h:
#ifndef _DEFAULT_FACTORY_H_
#define _DEFAULT_FACTORY_H_

#include "ifactory.h"

#include <vector>
#include <stdexcept>

class DefaultFactory : public IFactory {
public:
    int createNumber(const std::string& name, std::pair<int, int> range) override {
        for (auto factory: g_factories) {
            if (factory->getName() == name) {
                return factory->createNumber(name, range);
            }
        }

        throw std::runtime_error{"No factory can create requested number"};
    }

    std::string getName() const override {
        return "default";
    }

    static void registerFactory(IFactory* factory) {
        g_factories.push_back(factory);
    }

private:
    static std::vector<IFactory*> g_factories;
};
#endif

// defalut_factory.cpp
#include "default_factory.h"

std::vector<IFactory*> DefaultFactory::g_factories;

// even_factory.cpp
#include "default_factory.h"

class EvenFactory : public IFactory {
public:
    EvenFactory() {
        DefaultFactory::registerFactory(this);
    }

    int createNumber(const std::string& name, std::pair<int, int> range) override {
        return range.first % 2 == 0 ? range.first + 4 : range.first + 3;
    }

    std::string getName() const override {
        return "even";
    }
};

// Hopefully registers itself to the default factory
static EvenFactory evenFactory;

// main.cpp
#include "default_factory.h"

#include <iostream>

int main() {
    DefaultFactory factory;
    std::cout << factory.createNumber("even", {100, 200}) << std::endl;
}

# Makefile:
all: foo

foo: libdefault_factory.so libeven_factory.so main.cpp
    $(CXX) -L./ -o foo main.cpp -ldefault_factory -Wl,--no-as-needed -leven_factory

libdefault_factory.so: default_factory.cpp default_factory.h ifactory.h
    $(CXX) -shared -fPIC -o libdefault_factory.so default_factory.cpp

libeven_factory.so: even_factory.cpp default_factory.h ifactory.h
    $(CXX) -shared -fPIC -o libeven_factory.so even_factory.cpp

bar: default_factory.cpp even_factory.cpp default_factory.h ifactory.h main.cpp
    $(CXX) -o bar main.cpp default_factory.cpp even_factory.cpp

.PHONY: clean

clean:
    rm foo bar *.so

当我执行时，我得到一个运行时异常，该异常是从 抛出的，就好像构造函数没有运行一样。fooDefalutFactoryevenFactory

按预期运行打印。bar104

为什么不为构造函数调用？foo

注意：我使用 g++ 版本 9 和 g++ 版本 10.2 测试了该示例。