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jstarx@gmail.com · Guest

Hi, I'm having trouble understanding what's going on with my template
member functions. For example:

/////////////////////////////////////////////////////////////////
#include <iostream>
using namespace std;

//testClass1
class testClass1
{
public:
testClass1(int x = 0)
{ data = x; }
friend ostream& operator <<(ostream& out, const testClass1& source)
{ out << source.data; return out; }
template testClass1& operator =(const numericType& rhs)
{ *this = testClass1(rhs); return *this; }
private:
int data;
};

//testClass2
class testClass2
{
public:
testClass2(int x = 0)
{ data = x; }
friend ostream& operator <<(ostream& out, const testClass2& source)
{ out << source.data; return out; }
template testClass2& operator =(const numericType& rhs);
private:
int data;
};

template <class numericType>
testClass2& testClass2::operator =(const numericType& rhs)
{ *this = testClass2(rhs); return *this; }

//Main program
int main(int argc, char* argv[])
{
testClass1 a(1);
testClass2 b(1);
cout << a << ',' << b << " - ";
a = 2;
b = 2;
cout << a << ',' << b << endl;
return 0;
}
////////////////////////////////////////////////////////

In VC++ 6.0 this compiles and runs fine. But the output is "1,1 -
2,1". I don't know why the assignment operator isn't functioning the
way it should in testClass2. The only difference between the two
classes is the overloaded assignment operator. One is inline, one has
a seperate implementation. But both functions use exactly the same
code, so why the difference?

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thoth39 · Guest

Output with g++ 3.4 and g++ 4.0 is "1,1 - 2,2".

--
Pedro Lamarão

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Zedzed · Guest

this works correctly in VC++ 7.1 but I would have defined testClass1 as
follows:
class testClass1
{
public:
explicit testClass1(int x = 0)
{ data = x; }
testClass1& operator =(const testClass1& rhs)
{ data = rhs.data; return *this; }
testClass1& operator = (const int i) {
data = i; return *this; }
int getData() const
{
return data;
}
private:
int data;

};

ostream& operator <<(ostream& out, const testClass1& source)
{ out << source.getData(); return out; }

I am not sure I see the need for a template function.

and testClass2 in a similar way.

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Ismail Pazarbasi · Guest

Let me ask an awkward question; did you debug the code and see that it
hits assignment operator? If so, what are values before and after
function call?

Zedzed is right about class design. I did not test the code, but I
guess it works as expected.

Ismail

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Starx · Guest

The reason I am using a template function is because I would like my
constructor to be explicit but I would also like the assignment
operator to work with any data type that I have a constructor for. I
need the explicit to prevent the compiler from messing up the typecasts
and I'm overloading quite a few operators for quite a few data types,
I'd rather not write a function for each of them (it would be 80 or so
of them) so I was hoping a template function would do the trick.

I'm not sure how to use the debuger, but I did put output statements
into the assignment operator to see and they never get executed either.

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pavana.murthy@gmail.com · Guest

Answer is that VC6 deos not 'fully' support "template member function"
in "non-template" class. [Although standard allows it ]
The fact that VC6 compiles the above program is a bug in VC6 compiler(
see MSDN for Standard non-conformance page)

The above non- conformance has been fixed in VC7 compiler.
Of course gcc supports it

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