Is a global boolean variable reliable during global destruction?

Question

If I have a simple data type as a global variable -- like a boolean flag; specifically, something that doesn't have a destructor -- does that variable remain reliable even during global destruction? Or is that not guaranteed?

For example, would the result for the following code be well-defined?

Flag.h:

void SetFlagState(bool flag);
bool GetFlagState();

Flag.cpp:

#include <Flag.h>
namespace { // local declarations
bool g_flag; 
}

void SetFlagState(bool flag)
{
    g_flag = flag;
}
bool GetFlagState()
{
    return g_flag;
}

Main:

#include <iostream>
#include <Flag.h>

class FlagChecker
{
public:
    ~FlagChecker()
    {
        std::cout << "Flag value: " << GetFlagState() << std::endl;
    }
};
FlagChecker g_FlagChecker; // global instance; dtor will be called on exit

int main()
{
    SetFlagState(true);
}

Answer 1

Yes, this is safe. The lifetime of the storage is the duration of the program. The chief issue during that lifetime is with the moment of initialization (via your g_Flagchecker). As there's no such thing "de-initialization" for built-in types, your g_flag remains valid as long as there's code executing in your process.