Prev: How can I cotrol the position of the cursor in Word?
Next: Incremental linker VS2008
From: Fabian on 5 May 2008 06:59
Hello,

I have a struct defined as follows:

class ImageMetrics
{
public:
ImageMetrics(): Width(0), Height(0), BitsPerSample(0),
SamplesPerPixel(0), BytesPerPixel(0){}
int Width;
int Height;
int BitsPerSample;
int SamplesPerPixel;
int BytesPerPixel;
};

which is defined __dllexport. I have to compare whether two instances have
the same values (and I wanto to avoid comparing the members). Just using "=="
obviously doesn't work. So:

- (How) can I implement a "==" operator for a struct? Just a

bool operator == (ImageMetrics& CmpMetrics);

produces

error C2678: binary '==' : no operator found which takes a left-hand operand
of type 'Spimaging::ImageMetrics' (or there is no acceptable conversion)

- Should I make it a class?
- Is there another quick way?

Thanks for your help,

Fabian

From: Fabian on 5 May 2008 07:05

Appendix:

> Just a
> bool operator == (ImageMetrics& CmpMetrics);

Of course I would add a corresponding implementation like:

bool ImageMetrics::operator==( ImageMetrics& i_orCmpMetrics )
{
if ( (BitsPerSample == i_orCmpMetrics.BitsPerSample)
&& (BytesPerPixel == i_orCmpMetrics.BytesPerPixel)
&& (Height == i_orCmpMetrics.Height)
&& (SamplesPerPixel == i_orCmpMetrics.SamplesPerPixel)
&& (Width == i_orCmpMetrics.Width) )
return true;
else
return false;
}
From: Alex Blekhman on 5 May 2008 07:23
"Fabian" wrote:
> I have a struct defined as follows:
>
> class ImageMetrics
> {
> public:
> ImageMetrics(): Width(0), Height(0), BitsPerSample(0),
> SamplesPerPixel(0), BytesPerPixel(0){}
> int Width;
> int Height;
> int BitsPerSample;
> int SamplesPerPixel;
> int BytesPerPixel;
> };
>
> which is defined __dllexport. I have to compare whether two
> instances have
> the same values (and I wanto to avoid comparing the members).
> Just using "=="
> obviously doesn't work.

If your struct consists only of plain integers, then you can
compare it with `memcmp' function:

ImageMetrics im1 = ...
ImageMetrics im2 = ...

if(memcmp(&im1, &im2, sizeof(ImageMetrics)) == 0)
{
// identical
}

You can use `memcmp' withing `operator ==' as well (pay attention
to correct constness):

bool ImageMetrics::operator==(
const ImageMetrics& i_orCmpMetrics) const
{
return (
memcmp(&orCmpMetrics, this, sizeof(ImageMetrics)) == 0
);
}

HTH
Alex


From: Fabian on 5 May 2008 08:22
Hi Alex,

"Alex Blekhman" wrote:

> You can use `memcmp' withing `operator ==' as well (pay attention
> to correct constness):

Thanks a lot for the suggestion. But with this I still have the C2678. Any
ideas?

Thx,

Fabian
From: Alex Blekhman on 5 May 2008 08:38
"Fabian" wrote:
> Thanks a lot for the suggestion. But with this I still have the
> C2678. Any ideas?

Check again that you have the decrataion and the definition of the
`operator ==' are the same. The following code compies and runs
for me:

class ImageMetrics
{
public:
ImageMetrics(): Width(0), Height(0), BitsPerSample(0),
SamplesPerPixel(0), BytesPerPixel(0){}

bool operator ==(const ImageMetrics& other) const;

int Width;
int Height;
int BitsPerSample;
int SamplesPerPixel;
int BytesPerPixel;
};

bool ImageMetrics::operator ==(const ImageMetrics& other) const
{
return (memcmp(&other, this, sizeof(ImageMetrics)) == 0);
}

int main()
{
ImageMetrics im1;
ImageMetrics im2;

if(im1 == im2)
{
// equal
}

return 0;
}


Alex


 |  Next  |  Last
Pages: 1 2
Prev: How can I cotrol the position of the cursor in Word?
Next: Incremental linker VS2008