How to initialize static class varible by function return in C++?

Question

I have some class in .h file, for example:

class Test {
public:
    static const char* superData;
private:
    static const char* getSuperData();
};

then I want to init superData in .cpp file in such a way:

const char* Test::superData = getSuperData();

But when I get superData there is only some garbage.

const char* Config::getSuperData()
{
    char username[UNLEN + 1];
    DWORD username_len = UNLEN + 1;
    GetUserName(username, &username_len);

    return username;
}

If I call getSuperData() it gives me username, not garbage. Test::superData I call in my main() function.

Please create a [mcve] to show us. When and where do you have the definition and the initialization of the variable? When and where and *how* do you check the variable `superData`? What does the `getSuperData` function do? Shouldn't the `getSuperData` function also be `static`? — Some programmer dude, Jun 09 '19 at 10:04
[Can a local variable's memory be accessed outside its scope?](https://stackoverflow.com/q/6441218/3309790) — songyuanyao, Jun 09 '19 at 10:11

score 2 · Accepted Answer · answered Jun 09 '19 at 10:11

Your initialisation is correct but your definition of getSuperdata is flawed because you are returning a pointer to a stack based array. The array no longer exists once the function has been exited, so the pointer points at garbage.

The best way to avoid this kind of problem is to avoid pointers.

#include <string>

class Test {
public:
    static std::string superData;
private:
    static std::string getSuperData();
};

std::string Test::superData = getSuperData();

std::string Config::getSuperData()
{
    char username[UNLEN + 1];
    DWORD username_len = UNLEN + 1;
    GetUserName(username, &username_len);

    return username;
}

How to initialize static class varible by function return in C++?

1 Answers1