Undeclared identifier when it is obviously declared

Question

I have a code like the snippet below:

#include <map>
//using namespace std;

int main(){
constexpr int defval = -2e9;
struct defint
{
    int i = -defval;
    bool operator==(const int& j) { return i == j; }
    defint& operator=(int x) { i = x; return *this; }
};
std::map<char, defint> ci;
ci['a'] = 0;
}

This gives me C2065: 'defval': undeclared identifier at the line int i = defval;, but the defval is obviously declared before. How do I use the declared const in a struct or class so that the compiler sees it as it should? defval is not declared anywhere before the definition in the snippet and the error appears only when I add the line that makes use of the map, which is ci['a'] = 0;. The compiler I am using is the one from MSVS 2022 with the C++20 standard.

Answer 1

This seems to be a msvc bug and the program is well-formed.

Workarounds

There are two ways to solve this. Basically, msvc seems to have issue with defval not having static storage duration. So the ways just give defval static storage duration.

Solution 1

Here we add static constexpr to defval

int main(){
    //--------vvvvvv--------------------->added static
    constexpr static int defval = -2e9;
    //same code as before below
}

Working demo

Solution 2

Another way of giving defval a static storage duration is by making it global:

//no need to write static explicitly at global scope for constexpr variable
constexpr int defval = -2e9;
int main(){
   
    //same code as before here
}

---

Here is the newly submitted msvc bug:

MSVC rejects use of constexpr local variable when used with std::map