Program showing no output on console.

[patkipramod]

Hi all,

I am trying a program with friend function(max) which is common to 2 classes(XYZ and ABC). Here though compilation doesn't show any error/warning, I can't see expected output on console. So I tried to display something just to see if it comes on screen. But strange enough, nothing comes up on the screen.

Can you please have a look at the code below? Am I missing something? (specially to include any required header file)

#include <iostream>

class ABC;		//Forward declaration
//-----------------------------------------------------------------------------//

class XYZ
{
	int x;
public:
	void setvalue(int i) {x = i;}
	friend void max(XYZ, ABC);	
};
//-----------------------------------------------------------------------------//

class ABC
{
	int a;
public:
	void setvalue(int i) {a = i;}
	friend void max(XYZ, ABC);	
};
//-----------------------------------------------------------------------------//

void max(XYZ m, ABC n)	//Definition of friend
{
	if(m.x >= n.a)
		std::cout << m.x;	//no output
	else
		std::cout << n.a;	//no output
	std::cout << "Test1";	//for testing only
}
//-----------------------------------------------------------------------------//

int main()
{
	std::cout << "Test2";		//for testing only
	class ABC abc;
	abc.setvalue(10);
	XYZ xyz;
	xyz.setvalue(20);
	max(xyz, abc);
	std::cout << "Test3";		//for testing only
	return 0;
}

[MikeyBoy]

So you're not even getting "Test2" and "Test3" displayed in the console?

What OS are you using? What compiler/IDE?

Edit: Have you tried stepping through it with a debugger?

[patkipramod]

I am using g++ compiler on a GNU/Linux and don't have a debugger... :(
Just using crimson editor.
And yes, I am not getting Test1, Test2 or Test3 on screen

[MatthewRock]

How do you run this program? Afaik, this program will not do anything by itself - it won't start terminal; you have to either use it from terminal, or have some IDE provide you with their terminal for program to work.

[Lowest0ne]

A shot in the dark: You are naming the program "test" when you build it. Unix/Linux already have a program named test, so you are running that program and not yours. Try giving the absolute path:
$ ./test

Pro tip: If you aren't seeing "Test2" or "Test3" on console, you need to try this:

#include <iostream>

int main( void )
{
  std::cout << "hello world\n";
  return 0;
}

Knowing if that works changes the direction of your problem solving significantly.

[patkipramod]

Thanks for your inputs MatthewRock & LowestOne

@MatthewRock: I am compiling and running it from bash shell prompt like below
Compile:
-bash-3.00$ g++ Friend_Function_2Classes.cpp -o Friend_Function_2Classes

Run:
-bash-3.00$ ./Friend_Function_2Classes
Test220Test1Test3-bash-3.00$

@LowestOne: It worked. I added void in int main() as suggested by you and it showed output. Also to add, now when I remove void again from int main() and recompile and run it, it still shows output :-)

Can you please explain the reason behind this behavior?

[nvrmnd]

int main() and int main( void ) are both same ;

The latter is use to explicitly define that the function takes no arguments

[ne555]

The former is also used to explicitly define that the function takes no arguments

[MaxterTheTurtle]

Linux is kindof funky. I was using std::cout in constructors and it showed the output on Windows, but not on Linux. I don't think it is related, but Linux is a bit weird sometimes.

[TheIdeasMan]

@patkipramod

You should get into the habit of turning on all the warnings when compiling, use at least the g++ options -Wall -Wextra -pedantic.

To be really thorough, you can upgrade warnings to errors with -Werror.

Even though there are a zillion options, it is worth having a read of the gcc manual page.

There are others handy options to do floating point comparison & narrowing, default cases in switches, Plus other goodies.

Have fun.



Edit:

With int main( void ), it has never been a requirement for C++, Although it was for ANSI C - if my memory serves me correctly from 25 years ago!

[patkipramod]

Thank you all for your informative and wonderful replies.
@TheIdeasMan: I'll try to explore more gcc options and will make use of manual also. Thanks for the suggestion. :-)

I have started to enjoy c++