operator overload problem

I make a "+" overload for my class as what CString does but found it cannot give the right result.

Here is my code:

CmyClass& operator +(CmyClass& a, CmyClass& b)
{
CmyClass c(...);
// assign a+b value to c
return c;
}

and then if i run
CmyClass a, b, c;
c = a+b;
give a wrong c result;

I have thought about c is supposed to have only local lifetime, but CString does the same

this is what CString does:

CString AFXAPI operator+(const CString& string1, const CString& string2)
{
CString s;
s.ConcatCopy(string1.GetData()->nDataLength, string1.m_pchData, string2.GetData()->nDataLength, string2.m_pchData);
return s;
}

You return local object by reference, what is wrong. CString returns local object by value (so it's returning a copy of local object), what is OK. You have to change return valuefrom CMyClass& to CMyClass.

Cheers,
Hob

And for const correctness, CmyClass should be passed as const reference.

Hobson,

Thank you for your help. Actually that is a typo. But i do have it solved by your words of "copy object". I forgot to make a copy construct function. Thank you!

Hi,

Once i add const prefix, i got an error below while compiling.

error C2662: 'Func' : cannot convert 'this' pointer from 'const class CMyClass' to 'class CMyClass &'

in Func, i return a class member;

do you know what the problem is? Thank you!

Quote:

---

Originally Posted by SuperKoko

And for const correctness, CmyClass should be passed as const reference.

---

I got it. i forget to use const member funcion in the class with const reference.

sorry to bother. I haven't used c++ for a while, some basics just slip out of my mind. :)

Quote:

---

Originally Posted by olin

Hi,

Once i add const prefix, i got an error below while compiling.

error C2662: 'Func' : cannot convert 'this' pointer from 'const class CMyClass' to 'class CMyClass &'

in Func, i return a class member;

do you know what the problem is? Thank you!

---

http://www.codeguru.com/forum/showthread.php?t=401691