Simple C++ template question.

[moma]

Hello all,

I have created a template class for Point. The template can create a Point for several basic types such as Integer, Float and Double.

In this first example everything is OK, but the second example fails. Read on....

The first example:


template <typename T>
class Point
{
public:
T x;
T y;

Point() : x(0), y(0) {}

Point(T _x, T _y) : x(_x), y(_y) {}
};


int main()
{
Point<int> point(15,17);

Point<int> point2 = Point<int>(2,2);

return 0;
}

Compile and run
$ g++ -Wall main.cpp -o main
$ ./main

It's Ok.
----------------------------------------------------------------------------------

Example 2;
Now I want to extend the Point class with a 'copy constructor' and a function for operator '=' .


template <typename T>
class Point
{
public:
T x;
T y;

Point() : x(0), y(0) {}

Point(T _x, T _y) : x(_x), y(_y) {}

Point (Point &_other)
{
*this = _other;
}

Point &operator = (Point &_other)
{
x = _other.x;
y = _other.y;
return *this;
}

};

No changes in the main() functions.

Compilation fails. Do you know why and how to fix this? What happens?

/home/moma/code/test5/main.cpp:: In function ‘int main()’:
/home/moma/code/test5/main.cpp:98: error: no matching function for call to ‘Point<int>::Point(Point<int>)’
/home/moma/code/test5/main.cpp:65: note: candidates are: Point<T>::Point(Point<T>&) [with T = int]
:: === Build finished: 2 errors, 0 warnings ===
----------------------------------------------------------------------------------

I have also tried this but no success.


template <class T>
class Point
{
....

Point<T> (Point<T> &_other)
{
*this = _other;
}

Point<T> &operator = (Point<T> &_other)
{
x = _other.x;
y = _other.y;
return *this;
}

};

I thought I could do templates but now am quite confused.
TIA a lot.

[PandaGoat]

I am not exactly sure why this cause that error, but the arguments for the copy constructor and operator need to have the const keyword.



template <typename T>
class Point
{
public:
T x;
T y;

Point() : x(0), y(0) {}

Point(T _x, T _y) : x(_x), y(_y) {}

Point(const Point &_other)
{
*this = _other;
}

Point &operator = (const Point &_other)
{
x = _other.x;
y = _other.y;
return *this;
}

};

[moma]

Ok, thank you.

The const keyword fixed it. Now it compiles without errors.

Here is the code: http://www.futuredesktop.org/stdkit/basictypes.h