Member Avatar for pushpat

Hi folks,
I am learning operator overloading concept in c++, wrote sample program to test overloading of unary operator '!' and '-'.
Code will work if i use them as friend function but not for member function. Can anybody tell where am i going wrong in function bool operator!(const co_ordi &a) and co_ordi operator-(const co_ordi &x); . Is that correct way to declare and define.

I am getting following error
Error:
op_ovld_unary.cc:18: error: ‘bool co_ordi::operator!(const co_ordi&)’ must take ‘void’
op_ovld_unary.cc: In function ‘int main()’:
op_ovld_unary.cc:45: error: no match for ‘operator!’ in ‘!a’
op_ovld_unary.cc:45: note: candidates are: operator!(bool) <built-in>
op_ovld_unary.cc:50: error: no match for ‘operator-’ in ‘-b’
op_ovld_unary.cc:22: note: candidates are: co_ordi co_ordi::operator-(const co_ordi&)

#include<iostream>
using namespace std;

class co_ordi
{
	int cx,cy,cz;
	public:
	co_ordi(int x=0,int y=0,int z=0):cx(x),cy(y),cz(z)
	{
		cout<<"in c_tor="<<cx<<cy<<cz<<endl;
	}
	void get_coordi()
	{
		cout<<"x="<<cx<<"y="<<cy<<"z="<<cz<<endl;
	}
 // friend co_ordi operator- (const co_ordi &a);
 // friend bool operator! (const co_ordi &a);
 bool operator!(const co_ordi &a)
	{
		return (a.cx == 0 && a.cy == 0 && cz==0);
	}
	co_ordi operator-(const co_ordi &x)
	{
		co_ordi k(-x.cx,-x.cy,-x.cz);
		return k;
	}
		     
};
/**co_ordi operator- (const co_ordi &x)
{
	cout<<"me minus"<<endl;
	return co_ordi(-x.cx,-x.cy,-x.cz);
}
bool operator! (const co_ordi &a)
{

	return (a.cx == 0 && a.cy == 0 && a.cz == 0);
}**/


int main()
{
	co_ordi a,b(4,5,6);

	if(!a)
	cout<<"a at origin"<<endl;
	else
		cout<<"a not at origin"<<endl;
	b.get_coordi();
    b =	-b;
    b.get_coordi();
	return 0;
}
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  • Latest Post Latest Post by pushpat

Dani AI

Generated

Short explanation: the compiler message “‘must take ‘void’’” is telling you that, as a member, a unary operator already has the left-hand operand as this — so it must be declared with no parameters. pointed that out correctly and ’s change fixed the immediate error. The original errors happened because the compiler saw your member operator!/operator- with a parameter and therefore treated them as binary operators (which does not match expressions like !a or -b).

A slightly safer production form is to make these operators const (and optionally noexcept) since they do not modify the object. Example improved signatures:

bool operator!() const noexcept { return cx == 0 && cy == 0 && cz == 0; }
co_ordi operator-() const noexcept { return co_ordi(-cx, -cy, -cz); }

Notes and practical tips:

  • If you prefer a boolean conversion so if(a) works, implement an explicit conversion instead of relying only on operator!:

    explicit operator bool() const noexcept { return cx!=0 || cy!=0 || cz!=0; }

    Using explicit (C++11+) avoids unwanted implicit conversions. With an operator bool, !a becomes the built-in negation of that bool.

  • Member vs non-member: a non-member (friend) unary operator takes one parameter (the operand). A member unary operator takes zero parameters. For binary a - b as a member, declare a single-parameter operator-(const co_ordi& rhs) const; as a non-member you would take two parameters.

  • Const correctness matters: if you need to call the operator on const objects or temporaries, mark it const. Return by value for unary operator- (you are producing a new object).

— your fix was the right direction; the above tweaks (const/noexcept/explicit bool) will make the behavior more robust and predictable.

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Member Avatar for Caligulaminus

op_ovld_unary.cc:18: error: ‘bool co_ordi::operator!(const co_ordi&)’ must take ‘void’

i.e. bool co_ordi::operator!() must not take const co_ordi& .

Member Avatar for pushpat

Thank you Caligulaminus :).. I made the changes and its working

bool operator!()
	{
		return (cx == 0 && cy == 0 && cz==0);
	}
	co_ordi operator-()
	{
		co_ordi k(-cx,-cy,-cz);
		return k;
	}
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