C string as template non-type parameter works in gcc 6.3 but does not work in Visual Studio 2017 (19.16.27027.1 for x64)

Question

The following code:

#include <iostream>

template<const char* Pattern> void f() {
    std::cout << Pattern << "\n";
}

static constexpr const char hello[] = "Hello";

int main() {
    f<hello>(); //Microsoft (R) C/C++ Optimizing Compiler Version 19.16.27027.1 for x64
    //  Copyright (C) Microsoft Corporation.  All rights reserved.
    //
    //  string-as-template-parameter.cpp
    //  string-as-template-parameter.cpp(10): fatal error C1001: An internal error has occurred in the compiler.
    //  (compiler file 'msc1.cpp', line 1518)
    //   To work around this problem, try simplifying or changing the program near the locations listed above.
    //  Please choose the Technical Support command on the Visual C++
    return 0;
}

works when compiled by gcc (g++ (Debian 6.3.0-18+deb9u1) 6.3.0 20170516) but results in C1001 when compiled by VS 2017.

As a workaround I use:

#include <iostream>

template<const char** Pattern> void f() {
    std::cout << *Pattern << "\n";
}

static const char* hello = "Hello";

int main() {
    f<&hello>();
    return 0;
}

Does anybody have idea of more beautiful solution? May be initial code has an error which is skipped by gcc?

Answer 1

Does anybody have idea of more beautiful solution?

You can use a reference to std::string instead.

#include <iostream>
#include <string>

template<std::string & Pattern> void f() {
    std::cout << Pattern << "\n";
}

static std::string hello = "Hello";

int main() {
    f<hello>(); 
    return 0;
}

This compiles with MSVC in Visual Studio.

This works because as per Cppreference, a named lvalue reference with linkage is allowed as a non-type parameter. (Note that hello is not local.)