Deferring C++ static object construction - GCC on Linux

Question

Imagine I have a C++ class called MyClass.

Imagine that I have no access to the source code of MyClass ... it is contained in a library and I am supplied only the library and the header file for MyClass.

Imagine that the class itself requires environment pre-configuration ... for example ... before the constructor of the class can be called, I need to do some setup. The class is normally meant to be used as follows:

void func() {
   doGlobalSetup();
   MyClass myInstance(1,2,3);
   myInstance.doSomething();
   ...
}

Now I have the situation where we need to create a global instance of the class such as:

MyClass myInstance(1,2,3);

int main(int argc, char *argv[]) {
   doGlobalSetup();
   myInstance.doSomething();
}

The problem is that in this story, the instance of MyClass is created before the call to doGlobalSetup(). It is instantiated before main() is called. What I want to do is either defer the creation of myInstance() till later or be able to run doGlobalSetup() somehow before the instantiation of the class.

This is a simplification of the actual story ... so let us assume:

1. I can't change the internals of MyClass.
2. There must be an instance variable called myInstance of type MyClass (I can't change the logic to MyClass *pMyInstance).

Many thanks for reading.

Answer 1

Since you've constrained the problem such that new cannot be used, you should be able to create the object as always and copy it to the global instance. For example:

MyClass createMyClass()
{
    doGlobalSetup();
    return MyClass(1, 2, 3);
}

MyClass myInstance = createMyClass();

int main()
{
    myInstance.doSomething();

    return 0;
}

Answer 2

Does it suit your needs?

namespace
{
    int doStaticGlobalSetup()
    {
        doGlobalSetup();
        return 0;
    }
}
MyClass myInstance(doStaticGlobalSetup() + 1,2,3);

int main() {
   myInstance.doSomething();
   return 0;
}