class - Unresolved external symbol C++

Question

I ahve a problem with a code below:

ProgrammSettings.h

#pragma once
static class ProgrammSettings
{
public:
    static int fd;
};

Settings.cpp

#include "ProgrammSettings.h"

static bool LoadSettings()
{
    ProgrammSettings::fd = 2; // here error Unresolved symbol!!
    return true;
}

What i'm doing wrong? Thanks!

Answer 1

Unlike instance variables that require only a declaration, static member variabs of the class must also be defined.

Currently, your code contains only a declaration. Add a definition of your static fd variable to a cpp file to fix the error:

int ProgrammSettings::fd;