How to define string literal with character type that depends on template parameter?

Question

template
class StringTraits {
public:
    static const CharType NULL_CHAR = \'\\0\';
    static constexpr CharType* WHITESPACE_STR = \" \";
};

         


        

Answer 1

I've just came up with a compact answer, which is similar to other C++17 versions. Similarly, it relies on implementation defined behavior, specifically on the environment character types. It supports converting ASCII and ISO-8859-1 to UTF-16 wchar_t, UTF-32 wchar_t, UTF-16 char16_t and UTF-32 char32_t. UTF-8 input is not supported, but more elaborate conversion code is feasible.

template 
constexpr auto any_string(const char (&literal)[S]) -> const array {
        array r = {};

        for (size_t i = 0; i < S; i++)
                r[i] = literal[i];

        return r;
}

Full example follows:

$ cat any_string.cpp 
#include 
#include 

using namespace std;

template 
constexpr auto any_string(const char (&literal)[S]) -> const array {
        array r = {};

        for (size_t i = 0; i < S; i++)
                r[i] = literal[i];

        return r;
}

int main(void)
{
    auto s = any_string("Hello");
    auto ws = any_string(", ");
    auto s16 = any_string("World");
    auto s32 = any_string("!\n");

    ofstream f("s.txt");
    f << s.data();
    f.close();

    wofstream wf("ws.txt");
    wf << ws.data();
    wf.close();

    basic_ofstream f16("s16.txt");
    f16 << s16.data();
    f16.close();

    basic_ofstream f32("s32.txt");
    f32 << s32.data();
    f32.close();

    return 0;
}
$ c++ -o any_string any_string.cpp -std=c++17
$ ./any_string 
$ cat s.txt ws.txt s16.txt s32.txt 
Hello, World!