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I'm using a cross compiler. My code is:
class WindowsTimer{ public: WindowsTimer(){ _frequency.QuadPart = 0ull; } private: static LARGE_INTEGER _frequency; }; I get the following error:
undefined reference to `WindowsTimer::_frequency'
I also tried to change it to
LARGE_INTEGER _frequency.QuadPart = 0ull; or
static LARGE_INTEGER _frequency.QuadPart = 0ull; but I'm still getting errors.
anyone knows why?
529
When we declare a member of a class as static it means no matter how many objects of the class are created, there is only one copy of the static member. A static member is shared by all objects of the class. All static data is initialized to zero when the first object is created, if no other initialization is present.
An “Undefined Reference” error occurs when we have a reference to object name (class, function, variable, etc.) in our program and the linker cannot find its definition when it tries to search for it in all the linked object files and libraries.
The static member functions are special functions used to access the static data members or other static member functions. A member function is defined using the static keyword. A static member function shares the single copy of the member function to any number of the class' objects.
Because static member variables are not part of the individual class objects (they are treated similarly to global variables, and get initialized when the program starts), you must explicitly define the static member outside of the class, in the global scope.
You need to define _frequency in the .cpp file.
i.e.
LARGE_INTEGER WindowsTimer::_frequency; With C++17, you can declare your variable inline, no need to define it in a cpp file any more.
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