Question

I have some global variables (classes) that as I understand have created before main() call. I need some technique to add data to a List of something either global or as member of that class from any part of my code and it have to be filled before Linker. To use it inside globally created classes. Is it possible? I did not find any similar solution or even question, so any help will be appreciated.

Detailed example:

I’ve have singleton class which has a variable that was filled in the constructor. All other classes use data from the class at run time someone early someone later. Singleton class is created at the begin of main function. I am using singleton in different projects, data that it has mostly universal for all projects and modules except special flag which should show requirement for this module. If singleton throw exception program exits and we know it at the first steps of execution because singleton creates at first lines of the main. So singleton has a lot of universal data for all projects but I need to add flags to point for singleton which data is required for each module. I have created template for main so for each project I have the same main with just simple define PROJECT_NAME later I add .cpp to the project and they have to register which data is required and which not.

This explanation not looks like perfect, if it is not understandable don’t hesitate to say it I will organize it more deliberately.

Edited:

I’m still looking for solution in the Internet, and found constexpr it looks like what I need, but at this moment it is not supported by all compilers, is there some workaround ?

Answer 1

First step is to not use global variables, but instead use static variables within a global function. The first time the function is called the variable will be initialized and then have the function return a reference to the varaible.

my_class& instnace() {
   static my_class i;
   return i;
}

A list example:

std::list<my_class>& global_list() { 
   static std::list<my_class> m; return m;
}


static int x = []()->int{ global_list().push_back(my_class); return 0;}();