Conditional Statement with color type

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Hello Everyone
I have written such code like this

C++

UINT width = bmp->GetWidth();
UINT height = bmp->GetHeight();

cout << "The Width is   " << width;
for(i=0;i<width;i++)>
{
	//cout << "Tes";
	for(j=0;j<height;j++)>
	{

	   bmp->GetPixel(i,j,&color);
	   if(color = 255,255,255)
	   {
				
		mxCoordinateX[l]= i;l++;
	        mxCoordinateY[m]= j;m++;
				
	   }
        }
}

but there was an error in run time regarding argb

C++

Status status = SetStatus(DllExports::GdipBitmapGetPixel(
static_cast<gpbitmap>(nativeImage),
x, y,        
&argb));

my program wants get coordinate of rectangle (unfilled, just line) in a white-background bitmap by check if the pixel is black then save the coordinates but error appeared i showed it above..
Could you give me advice?
Thanks

Posted 25-Sep-11 13:56pm

Kay Andrian Fikar

Updated 25-Sep-11 14:22pm

walterhevedeich

v2

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Philippe Mori · Answer 1 · 2011-09-25T14:43:00

Solution 1

The line

C++

if(color = 255,255,255)

probably does do what you think it does.

First, in C++, operator = is assignment operator and not equality operator.

Second, in C++, a comma allows multiple expressions when normally one expression is expected and the result is taken from the rightmost one.

Thus, that statement would essentially be equivalent to:

C++

255;
255;
color = 255;
if (color) { ... }

For more information, take a look at:
http://www.cplusplus.com/doc/tutorial/operators/[^]

And also:
http://msdn.microsoft.com/en-us/library/zs06xbxh(v=VS.100).aspx[^]

Posted 25-Sep-11 14:43pm

Philippe Mori

Comments

Sergey Alexandrovich Kryukov 25-Sep-11 22:29pm

Good catch of very basic C++ stuff, my 5.
--SA

Kay Andrian Fikar 26-Sep-11 0:18am

yes, when i type

if(color == 255,255,255)

it showed error Error :
error C2678: binary '==' : no operator found which takes a left-hand operand of type 'Gdiplus::Color' (or there is no acceptable conversion) c:\users\user\documents\visual studio 2008\projects\dasar imageprocessing\dasar imageprocessing\dasar imageprocessing.cpp

so color type cannot be used for conditional statements?
but i want to check if a black color exist in this pixel for example then i save the coordinate

Chuck O'Toole 26-Sep-11 2:41am

The message below is for you, I put the reply in the wrong place. Sorry.

Chuck O'Toole 26-Sep-11 3:21am

PS, 255,255,255 is not black, it's white (all colors full on). Black is 0,0,0

Chuck O'Toole 26-Sep-11 2:40am

No silly, it's not that you can't use a color type, it's that "255,255,255" are just 3 numbers. Oh, you wanted them to be treated as a "RGB()" value? Just how is the compiler to know that? Instead, create a 24 bit COLORREF value with "RGB(255,255,255)"

(oops, I replied to the wrong message, sorry)

Note, in your code shown, you do not define "color" but you obviously have it somewhere, care to share the definition with us?

mbue 26-Sep-11 13:56pm

Cannot understand the excitement nobody knows what color is. Assume it is:


class CColor
{
public:
	CColor()
	{
		_c = _d = 0;
	}
	CColor(CColor& c)
	{
		_c = c._c; _d = c._d;
	}
	
	operator COLORREF& (){ return _c; }

	template <class C> CColor& operator = (C c)
	{
		_d = c;
		return *this;
	}
	template <class C> CColor(C c)
	{
		_c=0; _d=c;
	}
	template <class C> CColor& operator , (C c)
	{
		_d = _d<<8|(c&0xFF);
		return *this;
	}
	operator bool ()
	{
		return _c==_d;
	}
private:
	COLORREF	_c;
	COLORREF	_d;
};

void GetPixel(int x,int y,COLORREF& c){ c = RGB(0,128,255); }

int FAR PASCAL _tWinMain(HINSTANCE h,HINSTANCE p,LPTSTR c,int sw)
{
	CColor	col;
	GetPixel(0,0,col);
	if(col = 255,255,255)
	{
		Beep(3000,100);
	}
	else
	{
		Beep(1000,100);
	}
	return 0;
}

and it works! So far
Regards.