C / C++ / MFC

31-Jan-18 12:00

So, I finally decided to dive into C++ world, trying to adapt some C# code I've been working on lately.
So here's what I have.
bin.h file:

C++

#pragma once

namespace Maths {

   class Bin
   {
      public:
         template <class T> static const T GetMask(int);
   };

}

bin.cpp file:

C++

#include "bin.h"

namespace Maths {

   template <class T> const T Bin::GetMask(int count) {
      return (T)0; // Fake implementation
   }

}

This compiles just fine. However, in the same console project, when I write:

C++

#include "bin.h"

using namespace Maths;

int main() {
   unsigned char value = Bin::GetMask<unsigned char>(0);
}

I get a nasty LNK2019 linkage error on compilation:

Error	LNK2019	unresolved external symbol "public: static unsigned char const __cdecl Maths::Bin::GetMask<unsigned char>(int)" (??$GetMask@E@Bin@Maths@@SA?BEH@Z) referenced in function "int __cdecl main(void)" (?main@@YAXXZ)

In the Bin class, I have a couple of other (non-generic) methods, which I can use just fine. I suspect a problem with static templated methods specifically, but I can't understand the core problem. Maybe I just try to do something which is not possible (using a static generic method), but I cannot figure out why it would not be possible.

Anyone could give me a hint on this?

"I'm neither for nor against, on the contrary." John Middle

Richard MacCutchan31-Jan-18 12:13

31-Jan-18 12:13

The Maths namespace does not contain a definition/declaration of Bin::GetMask<T>(int); only one of Bin::GetMask(int);. Just remove the <unsigned char> piece and it should be fine.

phil.o31-Jan-18 13:28

31-Jan-18 13:28

Thank you Richard for answering.
However, if I try to remove the <unsigned char> piece (namely: unsigned char value = Bin::GetMask(0);), the editor itself complains about the fact that no instance of function template "Maths::Bin::GetMask" matches the argument list.
Moreover, the Bin::GetMask<T>(int) is actually declared in Maths namespace. Problem seems to be with the .cpp part: the editor/IDE can see the definition of the generic method (since the editor does not complain when I try to use it, and the object explorer clearly displays the method with correct signature), but, on compilation, the linker cannot make a link to the actual implementation.
How can I correctly declare a static, generic method inside a non-generic class, then?
Thanks for your time Smile | :)

"I'm neither for nor against, on the contrary." John Middle

Richard MacCutchan31-Jan-18 21:41

31-Jan-18 21:41

phil.o wrote:
the Bin::GetMask<T>(int) is actually declared in Maths namespace.

I don't see it anywhere, unless that is somehow implied by template <class T> static const T GetMask(int);.

Hmm, I though I understood templates.

phil.o31-Jan-18 14:07

31-Jan-18 14:07

Anyway, I found the issue. I cannot implement a template method in the .cpp file, like I did with other non generic methods. I moved the implementation of the generic method in the .h header file, and now everything is ok.
I guess I have to dig deeper in the translation unit concept Smile | :)

"I'm neither for nor against, on the contrary." John Middle

CPallini31-Jan-18 21:20

CPallini

31-Jan-18 21:20

Yes, that's it. Template method definitions should be in header files.

Richard MacCutchan31-Jan-18 21:48

31-Jan-18 21:48

phil.o wrote:
the translation unit concept

The only reason for creating header files is when you have a set of common definitions that need to be shared by multiple translation units. If you only have a single .cpp file then all the definitions can safely be put in there. The #include statement is recognised by the preprocessor which reads all the include files and creates a new text file containing all the included code followed by the user written C/C++ code, and passes that new composite to the actual compiler.

phil.o1-Feb-18 3:20

1-Feb-18 3:20

I have learnt it the hard way Smile | :)

This explains why everything was fine as far as the editor/IDE were concerned, and why the issue only occurred on the linking phase. That's quite confusing for a beginner.

"I'm neither for nor against, on the contrary." John Middle

Richard MacCutchan1-Feb-18 4:08

1-Feb-18 4:08

phil.o wrote:
quite confusing for a beginner.

and sometimes for the rest of us.

Explorer

Fedrer31-Jan-18 0:12

Fedrer

31-Jan-18 0:12

Hello,
I want to create application like windows explorer. I think I can use builtin tree and builtin list view.

I think there are some interface IShellFolderTree or IShellFolderList. Can you please guide me with any example/article?

Re: Explorer

Richard MacCutchan31-Jan-18 0:49

31-Jan-18 0:49

See Getting Information About the Contents of a Folder (Windows)[^]. You can also use Google/Bing to do your own searches.

Re: Explorer

Jochen Arndt31-Jan-18 1:22

Jochen Arndt

31-Jan-18 1:22

The IShellFolder interface is mainly used to manage folders and provide data for clipboard and drag & drop. I suggest to start without using that and implement the tree and list views using standard API functions like FindFirstFileEx and FindNextFile which provide basic information like size, time stamps and attributes.

For additional info like icons and file types use SHGetFileInfo.

To get the owner name for a file or directory use GetNamedSecurityInfo and LookupAccountSid.

Solutions to resolve reparse points (links and mounts) can be found in the web (open with CreateFile with flags FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT and call DeviceIoControl with FSCTL_GET_REPARSE_POINT).

To use the IShellFolder interface you have to get the DesktopFolder and use that to bind to other folders:

C++

LPSHELLFOLDER pDesktopFolder;
::SHGetDesktopFolder(&pDesktopFolder);

LPSHELLFOLDER psfFolder = NULL;
LPITEMIDLIST pFolderPIDL = ::ILCreateFromPath(lpszPath);
HRESULT hRes = pDesktopFolder->BindToObject(
    pFolderPIDL,
    NULL,
    IID_IShellFolder,
    IID_PPV_ARGS(&psfFolder)
);

// Example to get the PIDL of a named file or folder within a folder
// This PIDL can then be used for other IShellFolder operations
LPITEMIDLIST pPIDL;
CString strName; // name within folder
hRes = psfFolder->ParseDisplayName(
    NULL,		 // no hWnd necessary when showing no dialog
    NULL,		 // no bind context
    strName.GetBuffer(), // non-const LPWSTR
    NULL,		 // no need to get number of parsed characters
    &pPIDL,		 // PIDL relative to the parsing folder
    NULL		 // attributes not used
);
strName.ReleaseBuffer();

// Releasing
::CoTaskMemFree(pPIDL);
psfFolder->Release();
::ILFree(pFolderPIDL);
pDesktopFolder->Release();

As you can see there are lot of tasks where some are quite complex.

Re: Explorer

Randor 31-Jan-18 5:26

Randor

31-Jan-18 5:26

Hi,

It's alot of work and you will need alot of COM[^] and shell expertise[^]. Have a look at the explorer clone by David Erceg:

Explorer++ is a small and fast file manager for Windows.[^]

It comes with full source code.[^]

Best Wishes,
-David Delaune

Size of a window

Anthony Appleyard29-Jan-18 5:05

Anthony Appleyard

29-Jan-18 5:05

HWND hWnd;

After that declaration, please, how can I find the total outside size of the current window including the window's frames and menu and any scroll bars etc, not only the window's available area for writing text and images in?

OriginalGriff29-Jan-18 5:07

OriginalGriff

29-Jan-18 5:07

Once you have the window handle, you just call GetWindowRect[^]

Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!

Victor Nijegorodov29-Jan-18 10:49

Victor Nijegorodov

29-Jan-18 10:49

There are some window functions you can use: Window Functions (Windows)

Anthony Appleyard31-Jan-18 5:56

Anthony Appleyard

31-Jan-18 5:56

Thanks.

SetWindowPos() sets up a window, and needs the desired total window size including borders and scroll bars etc.

Can I find easily the values of the needed total window size (say xj and yj) needed to set up a window whose image-and-text area (= client area) is xi * yi)?

Richard MacCutchan31-Jan-18 6:05

31-Jan-18 6:05

Use GetWindowRect and GetClientRect to find those two values. The difference is the size of the frame portion. You can then calculate your required client size, add that to the frame sizes to get your new window size.

Class as a DLL

ForNow24-Jan-18 5:37

ForNow

24-Jan-18 5:37

Just read an article on using classes as a DLLs following the class a __declspec(dllimport/dllexport) is needed. I was just wondering how MFC does it. On my system the MFC code is located in MFC140.DLL now when I inherit a let’s say CDialog class I don’t specify __declspec(dllimport)
Thanks

Richard MacCutchan24-Jan-18 6:51

24-Jan-18 6:51

ForNow wrote:
I don’t specify __declspec(dllimport)

No because that declaration will be in the header file. You should take a look at Creating and Using a Dynamic Link Library (C++)[^] for more information. Basically the project that creates the dll needs __declspec(dllexport) and every application the wants to use it needs __declspec(dllimport). This is usually controlled by a #define in the header that goes with the dll. If you create a DLL project in Visual Studio and select the "Export Symbols" checkbox, you get the following in the header:

C++

// The following ifdef block is the standard way of creating macros which make exporting 
// from a DLL simpler. All files within this DLL are compiled with the WIN32PROJECT2_EXPORTS
// symbol defined on the command line. This symbol should not be defined on any project
// that uses this DLL. This way any other project whose source files include this file see 
// WIN32PROJECT2_API functions as being imported from a DLL, whereas this DLL sees symbols
// defined with this macro as being exported.
#ifdef WIN32PROJECT2_EXPORTS
#define WIN32PROJECT2_API __declspec(dllexport)
#else
#define WIN32PROJECT2_API __declspec(dllimport)
#endif

// This class is exported from the Win32Project2.dll
class WIN32PROJECT2_API CWin32Project2 {
public:
	CWin32Project2(void);
	// TODO: add your methods here.
};

extern WIN32PROJECT2_API int nWin32Project2;

WIN32PROJECT2_API int fnWin32Project2(void);

ForNow24-Jan-18 7:28

ForNow

24-Jan-18 7:28

Thanks I was just curious how MFC does it the code is in MFC140.DLL
and I don’t see any __declspec(import)
When I want to use CDialog

Also I assume when I follow theses steps in my .dll I’ll create a .lib

Thanks

Richard MacCutchan24-Jan-18 7:51

24-Jan-18 7:51

The exported labels are not in the dll, as that means nothing to the compiler. They are in one of the header files somewhere in the MFC include folders. So if you find the definition of CDialog it will somehow be defined there.