Help! Operator + problems

[Timothy Stark]

Hello folks,

I am trying get operator + working. I developed a class for a pair (left
and right values).

class Word10 {
public:
uint18 left, right;

:
:

inline Word10& operator += (const Word10& val)
{
if ((right += val.right) & H10_MASK)
(right &= H10_MASK, left++);
left = (left + val.left) & H10_MASK;
return *this;
}
};

inline Word10& operator + (const Word10& x, const Word10& y)
{ return Word10 (x) += y; }

:
:

Word10 x(2, 2), y(3, 3), z;

z = x + y;

cout << "Z = (" << z.left << "," << z.right << ")" << endl;

I tried to print but it did not work. It crashed with segmentation fault or
incorrect result of sum (scrambled results). However, it works so well with
using += operator. Does anyone have resolve the problem with that? I am
using GCC C/C++ compiler.

Thank you!
Tim

[James Lothian]

Re: Help! Operator + problems

Timothy Stark wrote:[color=blue]
>
> Hello folks,
>
> I am trying get operator + working. I developed a class for a pair (left
> and right values).
>
> class Word10 {
> public:
> uint18 left, right;
>
> :
> :
>
> inline Word10& operator += (const Word10& val)
> {
> if ((right += val.right) & H10_MASK)
> (right &= H10_MASK, left++);
> left = (left + val.left) & H10_MASK;
> return *this;
> }
> };
>
> inline Word10& operator + (const Word10& x, const Word10& y)
> { return Word10 (x) += y; }
>
> :
> :
>
> Word10 x(2, 2), y(3, 3), z;
>
> z = x + y;
>
> cout << "Z = (" << z.left << "," << z.right << ")" << endl;
>
> I tried to print but it did not work. It crashed with segmentation fault or
> incorrect result of sum (scrambled results). However, it works so well with
> using += operator. Does anyone have resolve the problem with that? I am
> using GCC C/C++ compiler.
>
> Thank you!
> Tim[/color]

Those 36-bit machines are a pain, eh? I think the problem is that
operator+ is
returning a reference to a temporary. Removing the & (so that the result
is
returned by value) might be enough.

James

[Ron Natalie]

Re: Help! Operator + problems


"Timothy Stark" <sword7nospam@s peakeasy.org> wrote in message news:VZKdnTwgBo 3J-xKiRTvU2Q@speak easy.net...
[color=blue]
>
> inline Word10& operator + (const Word10& x, const Word10& y)
> { return Word10 (x) += y; }
>[/color]

operator+ should NOT return a reference. It should return a Word10 object
(by value). Just remove the first & on the line above and things shoud be fine.

The fact that the above even compiles is one of those insidious rvalue to
lvalue conversions. The object returned has ceased to be by the time you
reach the caller of operator+.