返回stack上变量的const ref

const_ref_return.cpp

#include <iostream>
#include <memory>
#include <vector>
#include <string>
using namespace std;

class TestVector
{
    public:
    ~TestVector()
    {
        cout << "Destruct TestVector" << endl;
    }
    void push_back(const string& str)
    {
        m_vector.push_back(str);
    }
    int size() const
    {
        cout << "m_vector location: " << (size_t)(&m_vector) << endl;
        return m_vector.size();
    }
    private:
    vector<string> m_vector;
};

const vector<string>& func()
{
    vector<string> result = {"test"}; 
    return result;
}

const vector<string>& func_return()
{
    return vector<string>{"test"};
}

const TestVector& func_class()
{
    TestVector test;
    test.push_back("test");
    cout << "func_class size in func " << test.size() << endl;    
    return test;
}

const string& func_str()
{
    string result("test");
    return result;
}

int main()
{
    const auto& result = func();
    cout << result.size() << endl;

    const auto& result_return = func_return();
    cout << result_return.size() << endl;    


    auto result_str = func_str();
    cout << result_str << endl;

    const auto& resultClass = func_class();
    cout << resultClass.size() << endl;    
    
    // 被析构的vector，如果调用它的成员函数是什么的结果？

    auto testVector = new vector<string>{"test"};
    cout << testVector->size() << endl;     // 输出1

    delete testVector;
    cout << testVector->size() << endl;      // 输出0

 /*
 所以这个最终表现的结果是，我调用了一个dangle的vector返回的结果
 两步：
 1. 返回的变量已经被析构
 2. 我调用已经析构变量的成员函数
 */

    // const vector<string>& testConstRef;
    // cout << testConstRef.size() << endl;
    return 0;
}