Templates Confusion

[baray98]

Guys I have this simple code on templates

#include <iostream.h>
#include <vector>
 
template <typename T>
class MyQueue
{
    std::vector<T> data;
public:
    void Add(T const &);
    void Remove();
    void Print();
};
 
template <typename T> void MyQueue<T> ::Add(T const &d)
{
    data.push_back(d);
}
 
template <typename T> void MyQueue<T>::Remove()
{
    data.erase(data.begin( ) + 0,data.begin( ) + 1);
}
 
template <typename T> void MyQueue<T>::Print()
{
    std::vector <double>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;
 
}
 
 
int main (int argc,char *argv[])
{
    MyQueue<double> q;
    q.Add(1.34);
    q.Add(2.24);
 
    cout<<"Before removing data"<<endl;
    q.Print();
 
    q.Remove();
    cout<<"After removing data"<<endl;
    q.Print();
    return 0;
}

#include <iostream.h>
#include <vector>

template <typename T>
class MyQueue
{
    std::vector<T> data;
public:
    void Add(T const &);
    void Remove();
    void Print();
};

template <typename T> void MyQueue<T> ::Add(T const &d)
{
    data.push_back(d);
}

template <typename T> void MyQueue<T>::Remove()
{
    data.erase(data.begin( ) + 0,data.begin( ) + 1);
}

template <typename T> void MyQueue<T>::Print()
{
    std::vector <double>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;

}


int main (int argc,char *argv[])
{
    MyQueue<double> q;
    q.Add(1.34);
    q.Add(2.24);

    cout<<"Before removing data"<<endl;
    q.Print();

    q.Remove();
    cout<<"After removing data"<<endl;
    q.Print();
    return 0;
}

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in my

template <typename T> void MyQueue<T>::Print()

method I want this iterator to be synchronize with my typename T

std::vector <double>::iterator It1;

std::vector <double>::iterator It1;

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meaning if i say

MyQueue<int> q;

MyQueue<int> q;

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the iterator should adjust himself to int, right now its always expecting a double.
Please help,
baray98

[lyuts]

Wouldn't it be right to have std::vector <T>::iterator It1; ? Or am i missing something?

[baray98]

I think you are missing something. The way that i can think of specialized template where if
T (in my case) is not double , then do something like this on the print method

template <typename T> void MyQueue <T>::Print()
{
    std::vector <double>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;
}
template <> void MyQueue<long>::Print()
{
    std::vector <long>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;
 
 
}
template <> void MyQueue<int>::Print()
{
    std::vector <int>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;
}
template <> void MyQueue<bool>::Print()
{
    std::vector <bool>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout <<std::boolalpha << *It1<<endl;
}

template <typename T> void MyQueue <T>::Print()
{
    std::vector <double>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;
}
template <> void MyQueue<long>::Print()
{
    std::vector <long>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;


}
template <> void MyQueue<int>::Print()
{
    std::vector <int>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;
}
template <> void MyQueue<bool>::Print()
{
    std::vector <bool>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout <<std::boolalpha << *It1<<endl;
}

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but now I want to extract the real printing itself and have just one method that will do this

// this is the real printing part 
It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout <<std::boolalpha << *It1<<endl;

// this is the real printing part 
It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout <<std::boolalpha << *It1<<endl;

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how can i have just one method to do all this on all type of T

baray98

[wysota]

What exactly is the problem? Is there an error message you could show us?

[baray98]

My problem is that in my class template method

template <typename T> void MyQueue<T>::Print(){
    std::vector <double>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;
 }

template <typename T> void MyQueue<T>::Print(){
    std::vector <double>::iterator It1;
    It1 = data.begin();
    for ( It1 = data.begin( ) ; It1 != data.end( ) ; It1++ )
        cout << " " << *It1<<endl;
 }

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this will only work for doubles since It1 is instantiated with doubles. I wanted to change this so that it will work on any T.

and the only thing i can think of is using special template and give each type a print method

baray98

[caduel]

replace

std::vector <double>::iterator It1;

std::vector <double>::iterator It1;

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by

typename std::vector<T>::iterator It1;
// Or make it a const_iterator since you do not want to modify things.
// For the same reason your method could (should) be declared const.

typename std::vector<T>::iterator It1;
// Or make it a const_iterator since you do not want to modify things.
// For the same reason your method could (should) be declared const.

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(You might want to provide a typedef for that in your class.)

HTH

[wysota]

If you want something to adjust "on the fly" then you can't do it with templates. What you want can probably be done with subclassing and virtual methods.