The same member function for 100 classes

[Tru]

Hello all.

Is it possible to declare and define a function once:

int MyFunc (int a, int b)
{
  int c;
  c=a+b;
  return c;
}

And use it in classes, say MyClass1 to MyClass100, without defining again?

class MyClass1 {
    // ...
  public:
    int MyFunc(int,int);
   // ...
}

Compiler doesn't see MyFunc from within the class as expected. Is there a way to make it work?

[Ganado]

You can define a function outside of a class, and then simply call it from any other function, whether in a class or not. You don't need to re-define the function 100 times.

[keskiverto]

"100 times"
I have an eerie feeling ...

Would you tell how MyClass2 and MyClass3 differ from each other?

[jonnin]

100 very similar classes implies a design problem. I would post more words here to see if someone can give you a better approach. Its doable, depending on what you want, in a number of ways, but you are throwing up all kinds of red flags that something isnt quite right.

[George P]

line 4 in your class snippet.....

friend int MyFunc(int,int);

[Tru]

@Ganado Thank you very much. It compiled and the exe worked. But it does not print anything. Am I missing something?

using namespace std;


int MyFunc(int a, int b)
{
	int c;
	c = a + b;
	return c;
}



class MyClass1 {
	// ...
public:
	int aa, bb;
	int cc;
	MyClass1(int, int);
	int sum(void);
	// ...
};

   MyClass1::MyClass1(int a0, int b0)
{
	aa = a0;
	bb = b0;
	cc = 0;
}

int MyClass1::sum(void)
{
	cc = MyFunc(aa, bb);
}




int main()
{
	MyClass1 mc1(2,3);
	mc1.sum();
	cout << "Print Test " << endl;
	cout << "Sum= " << mc1.cc << endl;
	return 0;
}

@keskiverto, @jonnin
Sorry about the number 100. I wrote it to emphasize my aim. But it will be definitely more than one. The function is coordinate transformation. It will transform coordinates in a class and transform displacements, forces, moment forces in other corresponding classes. It may increase.

[Ganado]

Turn on compiler warnings. Your sum function requires an int to be returned, but you don't return anything. But beyond that, it #worksforme, because I see 5 printed. But it's undefined behavior, so anything could happen.

Also, small tip: Next time, if you post a compilable example, also post the #includes, as it makes it so we don't have to type them ourselves.

[jonnin]

It may increase.
design as if it will, then.
you may want to use inheritance to re-use some code blocks, for example ... put ALL the reused stuff in one, and pull it into the others.... same idea just design it in by intent going forward.

[Tru]

@ Ganado:
It works now. Thank you. This is my first post, I will.

@jonnin:
I don't want to use classes because it will be multi multi inheritance which freaks me out. And there will be variable adjustments. May be I am thinking function oriented still because I just switched to object oriented.

[Tru]

And the working code is:

#include <iostream>

using namespace std;


int MyFunc(int a, int b)
{
	int c;
	c = a + b;
	return c;
}



class MyClass1 {
	// ...
public:
	int aa, bb;
	int cc;
	MyClass1(int, int);
	void sum(void);
	// ...
};

MyClass1::MyClass1(int a0, int b0)
{
	aa = a0;
	bb = b0;
	cc = 0;
}

void MyClass1::sum(void)
{
	cc = MyFunc(aa, bb);
}




int main()
{
	MyClass1 mc1(2, 3);
	mc1.sum();
	cout << "Print Test " << endl;
	cout << "Sum= " << mc1.cc << endl;
	return 0;
}

(Edit: Visual Studio 2019 with clang 10.0)

[George P]

Without headers that code does not compile.

[Tru]

@Furry Guy:
I got it now. Thanks. I added the .h content.