CODEWITHSUNDEEP
c++class
Dementor
Dementor

Reputation: 251

C++ generic classes

I have a (simple) question about generic classes in c++. I have some knowledge of using them in C# like list but now I tried to implement one in c++ and i have a error and I don't know what i should do for the program to work. This is not a homework or something i need to but its research for myself.

Code:

#include <iostream>
using namespace std;

template<class A>class genericClass
{
    A ceva;
    char* clasa;
public: 
    void afisClasa(void);
    genericClass(A);
    ~genericClass(void);
};

template<class A>genericClass<A>::afisClasa()
{
    cout << clasa;
}

template<class A>genericClass<A>::genericClass(A myType)
{
    myType = ceva;

    if((int)ceva == ceva)
    {
        clasa = "INT";
        goto label;
    }       

    if((float)ceva == ceva)
    {
        clasa = "FLOAT";
        goto label;
    }   

    if((double)ceva == ceva)
    {
        clasa = "DOUBLE";
        goto label;
    }   

    label:
    //cout << clasa;
}

template<class A>genericClass<A>::~genericClass(void)
{
}


int main()
{
    int n;

    genericClass<float> A(6.2);

    cin >> n;
}

This program is supposed to take a generic number and to say what type it is, but when i implement the afisClass method i get an error:

C4430: Missing type specifier - int assumed. Note c++ does not support default-in

Upvotes: 1

Views: 6469

Answers (2)

JaredPar
JaredPar

Reputation: 754893

This is a case where you'd likely want to do template specialization. C++ allows you to customize the behavior of a template based off it's instantiated type. For example 

template <typename T> 
void PrintMyType(T& arg) {
  cout << "Unknown type" << endl;
}

template <>
void PrintMyType<int>(int& arg) {
  cout << "int" << endl;
}

template <>
void PrintMyType<float>(float& arg) {
  cout << "float" << endl;
}

PrintMyType(42);  // prints "int"
PrintMyType("hello"); // prints "Unknown type"

Upvotes: 0

Kerrek SB
Kerrek SB

Reputation: 477150

You have to say:

template <class A> void genericClass<A>::afisClasa() { cout << clasa; }
//                 ^^^^

The function definition has to have the exact same form as the previous declaration.

Upvotes: 6

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