Solutions to Common Errors
Error LNK2001: unresolved external symbol _main
An unresolved external occurs when some code has a call to a function in another module
and the linker can't find that function in any of the modules or libraries that you are
currently linking to.
In this specific case, it means one of two things. Either you are trying to write a Win32
GUI application (or non-console application) and accidently compiled it as a Console
application... or you really are trying to compile a console application and didn't write or
properly compile in a main() function.
Generally the first is the most common, if you specify Win32 Console as the project type
in VC++ when you create your project you will get this error. You will also likely get it
if you try to compile from the command line using BC++ but you neglect to specify the
correct parameters to tell it to make a Win32 GUI application instead of a console app
which is the default.
Fixing
If you're using VC++ re-create your project and select the Win32 Application project type
(NOT "Console").
If you're using BC++ command line compiler, use -tW to specify a windows application.
Error C2440: cannot convert from 'void*' to 'HICON__ *' (or similar)
If you're compiling the code from this tutorial, it means that you are trying to compile it as
C++ code. The code is written for the bcc32 and VC++ C compilers, and as such may not compile
exactly the same under C++ since C++ has much stricter rules about converting types. C will
just let it happen, C++ wants to you to make it explicit.
VC++ (and most compilers) will automatically compile a file with a .cpp extension as C++ code, and
a file with a .c extension as C code. If you have added the tutorial code to a .cpp file, this
is the most likely reason of getting this error.
If you're compiling code not from this tutorial, I can't guarantee that it's correct and therefor
it may actually be an error that needs resolving. You'll have to use your own judgement to
determine if it's safe to cast the value and remove the error, or if you are actually trying
to make a variable be something it's not.
Fixing
If you want to use C, simply rename your file from .cpp to .c. Otherwise, simply add a cast, all of the
code in the tutorial will work without any other changes when compiled as C++.
For example, in C this will work:
HBITMAP hbmOldBuffer = SelectObject(hdcBuffer, hbmBuffer);
But in C++ requires a cast:
HBITMAP hbmOldBuffer = (HBITMAP)SelectObject(hdcBuffer, hbmBuffer);
Fatal error RC1015: cannot open include file 'afxres.h'.
Oddly enough, VC++ adds afxres.h to resource files even when you aren't using an MFC project, and yet
the file may only be installed if you install MFC. This perticular file isn't actually required, so to fix the error
you can edit the .rc file in notepad and replace both occurances of "afxres.h" with "winres.h"
(note that there should be two of them, and you need to change both).
Error LNK2001: unresolved external symbol InitCommonControls
You aren't linking to comctl32.lib which this API is defined in. This library is not included by
default so you will either need to add it to the libraries on your command line, or add it
in your VC++ project settings on the Link tab.
Dialog does not display when certain controls are added
Controls such as the ListView, TreeView, Hotkey, Progress Bar, and others are classified as Common Controls,
as they were added to windows in comctl32.dll and were not available prior to Windows 95. Controls such
as BUTTON, EDIT, LISTBOX, etc... while no doubt being common, are not "Common Controls" and I generally
refer to them as "Standard Controls".
If you add a Common Control to a dialog and it fails to display, you most likely failed to call InitCommonControls()
before running your dialog, or perhaps at all. The best place to call it is first thing in WinMain(). Calling
it in WM_INITDIALOG is too late, since the dialog will fail before it reaches this point and it will never
get called.
Some people and documentation may tell you that InitCommonControls() is deprecated and you should use InitCommonControlsEx().
Feel free to do this if you want, InitCommonControls() is just simpler and there's nothing wrong with using it.
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