return value for operator + ( ) overloading

Question

Why compiler doesn't return error if operator+() member function of date class is not returning anything. if i do

date d1,d2;
date any = d1 + d2;

then d1 + d2 will create a temporary, what does this temporary gets initialized with?

date operator+(date d)  
{  
    day += d.day; 
    month += d.month; 
    year += d.year; 
}

Note: its just for test purpose only. Not for commercial use or anything.

I also think you need to reconsider your implementation - otherwise you are going to get odd results like 60th of the 15th month! — Ed Heal, Feb 01 '12 at 08:37

score 4 · Accepted Answer · edited May 23 '17 at 11:48

4

Since, it's operator +() and not operator +=(), you should be creating a temporary and return the same:

date operator + (const date &d) const
{            //  ^^^^ 1         ^^^^^ 2
  date temp = *this;  // copy current object
  ...
  return temp;  // important: -Wall warned you for missing 'return'
}

There are other 2 important changes you can see:

(1) Passing d as const reference; because you don't need another copy

(2) Making operator + as const correct by adding const at end; because you are not going to modify this object

Update: For your updated question, here is a link which answers it.

Why “not all control paths return a value” is warning and not an error?

edited May 23 '17 at 11:48

Community

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answered Feb 01 '12 at 08:25

iammilind

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+1 for using a reference constant parameter. too many people use "stack" non-reference non-pointer arguments for non-predefined types! – vulkanino Feb 01 '12 at 08:27
1

It might be worth adding that the usual idiom here is 1) to make `operator+` a free function (but this is certainly not necessary unless there are implicit conversions to `date`) and 2) to implement it in terms of `operator+=`. (You've also got several instances of `data` which should be `date`.) – James Kanze Feb 01 '12 at 08:36
+1 for the sample code with the correct function prototype for operator+ – nitin_cherian Feb 01 '12 at 08:48
@vulkanino if a date is only a few bytes, pass-by-value could be faster – user253751 Mar 06 '14 at 06:05

score 2 · Answer 2 · answered Feb 01 '12 at 08:25

What does the following overloaded operator of date class should return? I see that it returns garbage.

You are not returning anything from the function, and hence the value returned is any randowm value and it is an Undefined Behavior.

You should return an object of the type Date explicitly by using :

return objName;

score 2 · Answer 3 · answered Feb 01 '12 at 08:26

2

You're modifying the first operand of +, which is incorrect. Get a copy and return it:

date operator+(date d) const { 
    date r = *this;
    r.day += d.day; r.month += d.month; r.year += d.year;
    return r;
}

answered Feb 01 '12 at 08:26

Yakov Galka

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score 0 · Answer 4 · answered Feb 01 '12 at 08:27

0

An object of type date.

You should construct a new date and not do the += of the various components. This is due to you wanting the + operator to behave in the traditional way as the + operator for numbers.

answered Feb 01 '12 at 08:27

Ed Heal

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score 0 · Answer 5 · answered Feb 01 '12 at 09:17

0

There is no way but create a new object to return. Don't worry about copying temporary object, most compilers would using NRVO here.

answered Feb 01 '12 at 09:17

Healer

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return value for operator + ( ) overloading

5 Answers5