c++ get dc in mfc application

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Hello,
O have this console application

C++

void main()
{
    double i,c,d,f,g,e;
	HDC hdc = GetDC(GetDesktopWindow());
    DWORD ret = GetDeviceCaps(hdc, HORZSIZE);
    DWORD ret2 = GetDeviceCaps(hdc, VERTSIZE);
    std::cout << "Your screen size in inches is " << ret/25.4 << "\" x " << ret2/25.4 << "\" \n";
    ReleaseDC(GetDesktopWindow(), hdc);
	i=ret/25.4;
	c=ret2/25.4;
d=0;
f=0;
d=((i*i)+(c*c));
g=sqrt(d);

Works correct, but in mfc I get an error here

C++

HDC hdc = GetDC(GetDesktopWindow());

says "cannot take 1 argument" is there any wrong typing in code, it is different in mfc?

And a second question : in c++ win forms application can I add as a dll pure native c++?

thank you

Posted 12-Dec-14 11:05am

Member 3892343

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Comments

Sergey Alexandrovich Kryukov 12-Dec-14 17:27pm

What you wrote cannot be related to MFC. I just don't see what did you link to the project and what did you #include.
Windows API's GetDC takes exactly one argument.
—SA

cariolihome 12-Dec-14 17:30pm

Try add :: (which means global context) to function calls:
::GetDC(::GetDesktopWindow())
Yes, You can:
http://msdn.microsoft.com/en-us/library/ms235282.aspx

Sergey Alexandrovich Kryukov 12-Dec-14 17:44pm

Exactly, but I'm not sure OP understands what it means; I provided more detailed answer, please see Solution 1.
I credited your comment, of course.
—SA

Richard MacCutchan 13-Dec-14 6:04am

There is nothing connected to MFC in your code. And you are missing an #include <windows.h>.

2 solutions

Solution 2

XML

#include "stdafx.h"
#include "tttest.h"
#include "tttestDlg.h"
#include <windows.h>
#include <iostream>
#include <complex>

Posted 12-Dec-14 19:55pm

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-12-12T11:38:00

For your first question, please see my comment to the question; see also:
http://msdn.microsoft.com/en-us/library/windows/desktop/dd144871%28v=vs.85%29.aspx[^],
http://msdn.microsoft.com/en-us/library/windows/desktop/ms633504%28v=vs.85%29.aspx[^].

Don't use MFC at this point. See the comment to the question by cariolihome: you can use scope operator '::', to indicate the use of the global namespace:
http://www.cplusplus.com/doc/tutorial/operators[^],
http://msdn.microsoft.com/en-us/library/5cb46ksf.aspx[^],
http://www.cplusplus.com/doc/tutorial/namespaces[^].

With MFC, you should have the instance of some window, so you don't need a HWND argument; instead, the instance "this" is used: http://msdn.microsoft.com/en-us/library/71eseab0.aspx[^].

(Do you understand how instance function calls work? You do have one extra (only one in this case) argument "this", which is implicit. It is used to pass the instance of the type to the method. And than, the implementation "knows" the HWND of this objects and uses it in the call to the Windows API's GetDC(HWND) I referenced above. Please see also my past answer: Catch 22 - Pointers to interface objects die when function using them is made static.[^].)

As to your second question…

Probably, you don't mean C++, but C++/CLI you could use with in .NET in general, System.Windows.Forms in particular. If so, you can use some unmanaged code in such project, too. The usual way is to use P/Invoke, but, with C++/CLI, you don't have to do it; it makes everything much simpler. You can create a mixed-mode (managed + unmanaged) project where you can freely combine .NET and unmanaged code. However, I would advise to keep some discipline. Separate your project in at least 3 distinct parts or layers: pure .NET (managed) part, pure unmanaged part, and the layer where you wrap unmanaged types in managed "ref" classes. Please see:
http://en.wikipedia.org/wiki/C%2B%2B/CLI[^],
http://www.ecma-international.org/publications/standards/Ecma-372.htm[^],
http://www.gotw.ca/publications/C++CLIRationale.pdf[^].

—SA