Trying to pass string literals as template arguments [duplicate]

Answer 1

re: your OP: I'd like to know why a couple of them failed.

The comment by @NatanReed is correct:

• Your first snippet fails because Get needs a TYPE and is given an object.
• Your second snippet fails because it is illegal to define a template argument as reference to an object.
  • until C++2003, that is. Then reference to an object became legal.

Template arguments must be constants from a limited set of types.

• See: ISO/IEC 14882-2003 §14.1: Template parameters
• See: ISO/IEC 14882-2003 §14.3.2: Template non-type arguments

And even then, the String constexpr str = "hello"; must have external linkage. So putting it on the stack inside of main() is not going to work.

Give this a try:

#include 
#include 

using namespace std;

struct String {
    char const *m_sz;

    constexpr String(char const *a_sz)
        :
    m_sz(a_sz) {}
};

template
string const Get() {
    return _rstr.m_sz;
}

extern String constexpr globally_visible_str = "hello";
int main() {
    cout << Get() << endl;
    return 0;
}