Constexpr for creating objects

问题

I'm trying to figure out if there is a performance gain of creating objects with constexpr instead of normally.

Here is the code snippet for constexpr.

class Rect
{
    const int a;
    const float b;
public:
    constexpr Rect(const int a,const float b)
    : a(a),b(b){}
};

int main()
{
     constexpr Rect rect = Rect(1,2.0f);
}

And without constexpr.

class Rect
{
    int a;
    float b;
public:
    Rect(int a, float b)
    : a(a),b(b){}
};

int main()
{
    Rect rect = Rect(1,2.0f);
}

I was expecting there will be a lot less code for constexpr since the memory should be initialized at compile-time.

Am I using constexpr properly? And if that is not true, can you use constexpr to create the objects at compile-time and then use them without any runtime overhead?

Thanks!

回答1:

It turned out that I had some headers included which were responsible for the similarity of the code.

The answer is that there is a big difference between both cases.

When compiling without optimizations, there is a substantial difference in the generated code... -cdhowie

来源：https://stackoverflow.com/questions/44678277/constexpr-for-creating-objects