The code is as follows:

//template_test.h
enum SnType
{
    Sa,
    Sb,
    Sc
};
//main.cc
#include <iostream>
#include "template_test.h"
using namespace std;
template<SnType _Tsn>
class Test
{
    public:
        void print()
        {
            cout << "Type is " << _Tsn << endl;
        }
    
};
int main()
{
    SnType type = Sa;
    switch (type)
    {
        case Sa:
            Test<Sa> A;
            break;
        case Sb:
            Test<Sb> A;
            break;
        case Sc:
            Test<Sc> A;
            break;
        default:
            break;
    }
    A.print();
    return 0;
}

when I run code , then the terminal shows the error: 'A' was not declared in this scope.

How can I use A out of the switch scop? Out of the switch scope, how can I use the template variable which is defined in switch scope in C Thanks a lot!

CodePudding user response：

How can I use A out of the switch scope?

You can't. It has ceased to exist.

Aside: All names that start with and underscore and are followed by a capital letter are reserved, _Tsn makes your program is ill-formed.

You'll have to do your type-dependant things within the switch, e.g.

#include <iostream>

enum SnType
{
    Sa,
    Sb,
    Sc
};

template<SnType Tsn>
class Test
{
    public:
        void print()
        {
            std::cout << "Type is " << Tsn << std::endl;
        }
    
};

template<SnType Tsn>
void testPrint()
{
    Test<Tsn>{}.print();
}

int main()
{
    SnType type = Sa;
    switch (type)
    {
        case Sa:
            testPrint<Sa>();
            break;
        case Sb:
            testPrint<Sb>();
            break;
        case Sc:
            testPrint<Sc>();
            break;
        default:
            break;
    }
    return 0;
}