GCC/Clang doesn't make temporary object

Question

class Sample {
private:
    int         data = 0;
    std::string name = nullptr;

public:
    Sample(int m_data, const std::string& pName) : data(m_data), name(pName) {
        std::cout << "Sample(int, const std::string&): " << name << "\n";
    }

    Sample(const Sample& rhs) : data(rhs.data), name(rhs.name) {
        std::cout << "Sample(const Sample&): " << name << "\n";
    }

    ~Sample() {
        std::cout << "~Sample(): " << name << "\n";
    }
}

Sample TestFunc(int param) {
    Sample a(param, "a");

    return a;
}

I've made a class like this and called TestFunc(20); in main(). Then following output came out.

Sample(int, const std::string&): a
~Sample(): a

I expected that a temporary Sample object is made so copy constructor should be called, but it wasn't.

This code has compiled with GCC & Clang, and with MSVC, copy constructor is called as I expect.

Sample(int, const std::string&): a
Sample(const Sample&): a  // temporary object constructor
~Sample(): a
~Sample(): a  // temporary object destructor

What is the problem with GCC/Clang?

https://stackoverflow.com/questions/12953127/what-are-copy-elision-and-return-value-optimization — VLL, Apr 01 '19 at 12:34
FWIW, it should never be a problem if a temporary is not created. If your code relies on it then it is broken. Temporaries cost resources so avoiding them is a good thing. — NathanOliver, Apr 01 '19 at 12:35
You're right. I'm just wondering why is it different by compiler. — EnDelt64, Apr 01 '19 at 12:37
With MSVS did you compile is release or debug mode? With GCC/Clang, what options did you use to compile the code? — NathanOliver, Apr 01 '19 at 12:37
CMake option in GCC: `-std=c++14 -m64 -pedantic -Wall -Wextra -Werror` — EnDelt64, Apr 01 '19 at 12:41

GCC/Clang doesn't make temporary object

0 Answers0