String literals not allowed as non type template parameters

Question

The following quote is from C++ Templates by Addison Wesley. Could someone please help me understand in plain English/layman\'s terms its gist?

Answer 1

It means you can't do this...

#include 

template 
void f() { std::cout << P << '\n'; }

int main()
{
    f<"hello there">();
}

...because "hello there" isn't 100% guaranteed to resolve to a single integral value that can be used to instantiate the template once (though most good linkers will attempt to fold all usages across linked objects and produce a new object with a single copy of the string).

You can, however, use extern character arrays/pointers:

...
extern const char p[];
const char p[] = "hello";
...
    f
();
...