My Issue with TcpListener listen() method

[KRS]

Hello! I'll be happy if someone will share their thought with me about this
Basically when

listen(unsigned short port);

is called like this

class C
{
        TcpListener l;
public:
        C() { l.listen(53000); };
};

C c;

int main()
{
        return 0;
}      

it prints in console
Failed to create socket

but if it's called like this

class C
{
        TcpListener l;
public:
        C() { l.listen(53000); };
};

int main()
{
        C c;
        return 0;
}

it's all good. Only difference I'm spotting is that in second variant, call is inside the main(). I want to know why is that happening, maybe I'm missing something. And is it connected with location like I noticed?

[Kvaz1r]

I think the reason in Zero initialization. Here is blog post with more human explanation - Initialization in C++ is bonkers.

[eXpl0it3r]

You'd have to trace the code to see what state isn't necessarily lining up.

But using global variables is highly discouraged and not really supported by SFML.

[Nexus]

A bit late, but the reason is not zero initialization -- both times, the same constructor is called, default-constructing the sf::TcpListener member variable.

As expl0it3r mentioned, initialization at startup (i.e. from global variables) is a big mess in C++, as there's no deterministic order. So better avoid global variables in general, good design almost always makes them obsolete.