There are a lot of restrictions on what a pointer-type template parameter can point to. In particular it needs to have linkage (which for example string literal

There are a lot of restrictions on what a pointer-type template parameter can point to. In particular it needs to have linkage (which for example string literals do not have). Whether the results of constexpr functions must, can or can't have linkage is beyond my paygrade, but I suspect this is an MSVC extension. edit: linkage appears to propagate through constexpr. So it depends on how ultimately the original string is generated. I don't know what guarantee the standard gives (cppreference doesn't mention anything and I can't be bothered to look at the standard).