CODEWITHSUNDEEP
c++templates
user1899020
user1899020

Reputation: 13575

Is it possible to make a string as a template parameter?

Is it possible to make a string as a template parameter and how? Like

A<"Okay"> is a type.

Any string (std::string or c-string) is fine.

Upvotes: 2

Views: 166

Answers (2)

Suedocode
Suedocode

Reputation: 2524

Here's one way to make the string contents determine uniqueness 

#include <windows.h> //for Sleep()
#include <iostream>
#include <string>

using namespace std;

template<char... str>
struct TemplateString{
    static const int n = sizeof...(str);
    string get() const {
        char cstr[n+1] = {str...}; //doesn't automatically null terminate, hence n+1 instead of just n
        cstr[n] = '\0'; //and our little null terminate
        return string(cstr); 
    }
};

int main(){
    TemplateString<'O','k','a','y'> okay;
    TemplateString<'N','o','t',' ','o','k','a','y'> notokay;
    cout << okay.get() << " vs " << notokay.get() << endl;
    cout << "Same class: " << (typeid(okay)==typeid(notokay)) << endl;
    Sleep(3000); //Windows & Visual Studio, sry
}

Upvotes: 1

James Kanze
James Kanze

Reputation: 153899

Yes, but you need to put it in a variable with external linkage (or does C++11 remove the requirement for external linkage). Basically, given:

template <char const* str>
class A { /* ... */ };

this:

extern char const okay[] = "Okay";

A<okay> ...

works. Note thought that it is not the contents of the string which define uniqueness, but the object itself: 

extern char const okay1[] = "Okay";
extern char const okay2[] = "Okay";

Given this, A<okay1> and A<okay2> have different types.

Upvotes: 2

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