How should I define and initialize a non-global namespace member variable?

Question

In my Memory.hpp file, I have a namespace boolean named isMHinit:

namespace Memory
{
    static bool isMHInit = false;
    DWORD HookFunction(LPVOID pTarget, LPVOID pDetour, LPVOID pTrampoline, BOOL isWriteCopy);
    static UINT64 CheckCodeAccess(UINT64 startaddress);
    DWORD OnAccessHookFunction(PVOID pTarget, LPVOID pDetour, LPVOID pTrampoline, BOOL isWriteCopy);
}; // namespace Memory

And inside Memory.cpp, I use and modify it:

// this function is a member of Memory, I removed most functionality for brevity.
DWORD HookFunction(LPVOID pTarget, LPVOID pDetour, LPVOID pTrampoline, BOOL isWriteCopy)
{
    if (!isMHInit) {
        if (MH_Initialize() != MH_OK) {
            std::cout << "Error: MHInit failed." << "\n";
            return 1;
        }
        isMHInit = true;
    }

When going through clang-tidy, I get this warning, even though I clearly modify it inside the function:

Variable 'isMHInit' is non-const and globally accessible, consider making it const

Is this an issue with clang-tidy, or should I modify something in my code?

Answer 1

You should never declare a variable static in a header (when it is not a class member). When a header contains

static bool isMHInit = false;

this means a separate variable isMHInit in each *.cpp file where the header is included. If you want to have a globally accessible variable shared between all source files, you can declare it as

inline bool isMHInit = false;

However, using non-const globally accessible variables is poor design, and Clang-tidy warns you about it.

If you actually use the variable in a single source file only, then keep your declaration as is but move it to the *.cpp file. This makes the design a little better.