How to create a global object for all project elements?

Question

C++ / C#

I want to create a global vector in the project. It is needed so that all forms / classes of the project have access to the same data. The problem is visible on the screenshot:

The screenshot shows part of the code (the global variable declaration itself) of the header.h file, which I include in the files where I want to use this vector.

Answer 1

The declaration of the tasks vector must be present in the corresponding cpp file (technically, in any other translation unit) besides extern in the h file in the screenshot. But generally speaking, there is a "singleton" pattern, it is much more feng shui for this situation.

Answer 2

Well , extern tells the compiler that somewhere (in some cpp module) this object is without extern.

Answer 3

In general, you should read about singletons in C ++, but if you are lazy, the safest option is the Myers singleton:

#include <string>

// Синглтон Майерса. Переменная str будет создана один раз при первом вызове getPrefix, начиная с c++11 это ещё и потокобезопастно.
const std::string& getPrefix(){ 
    static std::string str  {"pref::"}; // Инициализация должна быть в конструкторе. 
    return str;
}

// Его использование.
std::string addPrefix(const std::string& str){
    return getPrefix() + str; 
}