Undefined reference to a static member
C++Undefined ReferenceCross CompilingC++ Problem Overview
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?
C++ Solutions
Solution 1 - C++
You need to define _frequency
in the .cpp file.
i.e.
LARGE_INTEGER WindowsTimer::_frequency;
Solution 2 - C++
With C++17, you can declare your variable inline, no need to define it in a cpp file any more.
inline static LARGE_INTEGER _frequency;
Solution 3 - C++
Linker doesn't know where to allocate data for _frequency
and you have to tell it manually. You can achieve this by simple adding this line: LARGE_INTEGER WindowsTimer::_frequency = 0;
into one of your C++ sources.
More detailed explanation here
Solution 4 - C++
If there is a static variable declared inside the class then you should define it in the cpp file like this
LARGE_INTEGER WindowsTimer::_frequency = 0;
Solution 5 - C++
This is a full code example for this other question which is indeed a duplicate of this one.
#include <iostream>
#include <vector>
using namespace std;
class Car
{
public:
static int b; // DECLARATION of a static member
static char* x1(int x)
{
b = x; // The static member is used "not as a constant value"
// (it is said ODR used): definition required
return (char*)"done";
}
};
int Car::b; // DEFINITION of the static
int main()
{
char* ret = Car::x1(42);
for (int x = 0; x < 4; x++)
{
cout << ret[x] << endl;
}
return 0;
}