Pass by reference with template functions C++

Question

I'm Trying to make a template function and pass two variables to it by reference , every thing sounds good but it never compiled and the error message is :-

error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

I tried a small part of code and it gives me same error, any help please??

And this a part of code, the all other code is just like this:

int size , found = -1 ; 

template<class type> Read_Data( type &key , type &arr)
{ 
    cout << " please enter the size of your set \n " ; 
    cin >> size ;
    arr = new type[size]; 

    cout << " please enter the elements of your set : \n " ;
    for (int i = 0 ; i <size ; i ++ )
    {
        cout << " enter element number " << i << ": "  ;  
        cin >> arr[i] ;
    }
    cout << " please enter the key elemente you want to search for : \n " ;
    cin >> key ; 
}

void main(void)
{ 
    int key , arr ; 
    Read_Data (key, arr);

    /*after these function there is two other functions one to search for key 
    in array "arr" and other to print the key on the screen */ 
}

Answer 1

You are just missing a couple of things to get the code compiling (resolving the error you saw).

Basically, in int main(), you need to specify the type when instantiating the template, as in:

Read_Data <int> (key, value); 

so that the compiler knows what type you really want to instantiate it with.

Also note that the array should be of type int *. So in the templated function the signature has to change to:

template<class type> Read_Data( type &key , type* &arr)

This is the corrected code which won't show the error you were previously seeing:

#include<iostream>  

using namespace std;

int size , found = -1 ; 

template<class type> void Read_Data( type &key , type* &arr)
{ 
    cout << " please enter the size of your set \n " ; 
    cin >> size ;
    arr = new type[size]; 
    cout << " please enter the elements of your set : \n " ;

    for (int i = 0 ; i <size ; i ++ )
    {   
        cout << " enter element number " << i << ": "  ;   
        cin >> arr[i] ;
    }   

    cout << " please enter the key elemente you want to search for : \n " ;
    cin >> key;                                                                                                                                         
}

int main()
{   
    int key;
    int * arr;
    Read_Data<int> (key, arr);

    /* after these function there is two other functions one to search for key 
     * in array "arr" and other to print the key on the screen 
     */ 
}   

Answer 2

You need to specify a return-value type in the declaration of function Read_Data.

A few examples:

template<class type> void Read_Data( type &key , type &arr)
template<class type> int  Read_Data( type &key , type &arr)
template<class type> type Read_Data( type &key , type &arr)

The first example is probably what you need if you're not planning to return anything in that function...

BTW, you also need to:

• In function main, change int arr to int* arr.
• In function main, change Read_Data to Read_Data<int>.
• In function main, call delete[] arr after you finish using it.
• In function Read_Data, change type &arr to type* &arr.