CODEWITHSUNDEEP
c++classtemplates
Uwe_98
Uwe_98

Reputation: 919

Templates just work with inline definition

The following code works fine, when my template class is defined inline:

main
{
   unsigned int A=0;                       //local variable in  'main'.
   Test<int>  TestObjekt;   //Object.
   //do something
   cout<<TestObjekt.calculate_a(A);
};

The Class is just made 4 test reasons and it adds a '2' to the given data 'a' and it returns the result the local variable 'A' of main:

template <typename T> class Test        //dichiarazione classe
{
private: 
     T a;      //private variable of changeable type T.

public:               
  Test(T InitA)     //constructor
  {
     a=InitA;
  }

  T calculate_a(T a)  //method
  {
     a+=2;
     return a;
  }
};

In this way, everything works fine, but when I make an outline definition of the class, the compiler doesn't accept it anymore. Here is the decleration:

template <typename T> class Test        //class declaration
{
private: 
  T a;      //private variable

public:               
  Test(T InitA);  //constructor
  T calculate_a(T);  //method
};

Now my Definitions:

template <typename T>  Test<T>::Test(T InitA)
{
   a=InitA;
}

template <typename T> T Test<T>::calculate_a(T)  //metodo della classe Test
{
   a+=2;
   return a;
}

The error messages are the following:

1.error C2512: 'Test<T>': non è disponibile alcun costruttore predefinito...  
  means: there is no appropriate, predefined constructor available

1>        with
1>        [
1>            T=int
1>        ]

I'm using the Visual C++ 2008 Express Version Compiler. I'm a C++ beginner and I've neaerly had a nervous breakdown, because I'm already fighting a long time to make the program run.

Hope somebody could help me

Thanks and regards

Uwe

Upvotes: 0

Views: 114

Answers (2)

Panda
Panda

Reputation: 1239

The line Test<int> TestObjekt; is implicitly calling the default constructor Test<int>() which doesn't exist.

You either need to add arguments to your constructor call in your main: Test<int> TestObjekt(0);

Or, alternatively, define a constructor that doesn't require a value Test(){ \\do something }

Also the template definitions must be in the header file.

See this answer for a good explanation of why the definitions are required in the header.

Upvotes: 1

Nicholaz
Nicholaz

Reputation: 1429

In your main function, where an Test object is made, add a value to the constructor (make the TestObject with init-value): 

Test<int>  TestObjekt(0);   // Object with init value

or make a constructor that doesn't require a value, e.g. in your class declaration add a default value to the prototype of the constructor: 

Test(T InitA= 0);  //constructor with default value

Full version: 

template <typename T> class Test        //class declaration
{
    private: T a;      //private variable

    public:               
        Test(T InitA= 0);  // <<<-- either change here
        T calculate_a(T);  //method
};

Or change main: 

void main()
{
    unsigned int A=0;             //local variable in  'main'.

    Test<int>  TestObjekt(0);   // <<<--- change here.

    //do something
    printf("%d", TestObjekt.calculate_a(A));
};

Upvotes: 1

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