`f(g(),h())` is not UB. The order of evaluation of parameters is unspecified, but it's not undefined. They will be evaluated in some order before the call to `f

`f(g(),h())` is not UB. The order of evaluation of parameters is unspecified, but it's not undefined. They will be evaluated in some order before the call to `f()` takes place. If both functions modify the same global state, the order of modification is unspecified. It's still not undefined, and your use of global variables is still not recommended.