mCtrl  0.9.6
Design Notes

About Error Handling

In general, mCtrl follows Win32API conventions in error handling. On error, the mCtrl functions set the error code with SetLastError() and then typically return a value indicating an error has occurred. In most cases this error indicator is 0, -1, FALSE or NULL, depending on the function and type it returns.

If a function fails, any output parameters are undefined and you cannot rely on their value.

Also note that for the category of caller's programmatic errors (e.g. when application specifies an invalid value in a function parameter or invalid combination of multiple parameters; or when calling any function without having the particular mCtrl module initialized), mCtrl uses very pragmatic approach: Such error conditions are only checked if it is reasonably easy to do so. Some more checks can be enabled in debug builds of mCtrl.

About Strings

MCTRL.DLL supports Unicode and strings held internally in the library are encoded in Unicode.

However on interface level, MCTRL.DLL supports both Unicode and ANSI strings as well. If a function, message of a control or a structure uses string, there are usually two flavors of the entity: one for Unicode and one for the ANSI string. When calling a function or sending a message, ANSI strings in parameters and structure members are converted to Unicode on input and Unicode to ANSI on output.

Identifiers of the Unicode flavor then have the "W" suffix and ANSI have "A" suffix, in the same way as Win32API does. The public headers also provide preprocessor macros without the suffix, as an alias for the one of the two depending whether UNICODE is defined or not.

In case of notifications sent by control to the application, the mCtrl also follows the Windows custom practice: Controls which may need to send a notification with string data send WM_NOTIFYFORMAT message to its parent during creation and then respect the parent's desire.

This means you may use MCTRL.DLL easily in Unicode-enabled application as well as in ANSI applications.

About Initialization and Termination

mCtrl functionality is divided into several modules, each having its own public header file. Almost every module corresponds to an implementation of one GUI control. With few trivial exceptions, each module has its own initialization and termination function.

Before you may use any functionality of the module you have to initialize it and after you stop using it you should terminate it to free any resources the module uses.

For controls, the initialization routine typically registers the control's window class with RegisterClass(), and the termination function unregisters it with UnregisterClass().

Note that for performance reasons mCtrl functions do not test whether the module is properly initialized, so the function can fail in any means if the module is not initialized, or can work if the function does not currently rely on the initialization. But note that in the latter case there is no guaranty the behavior does not change in future versions of mCtrl.

The initialization function can be always called multiple times (even concurrently for multiple threads). Each module has its own initialization counter, incremented in the initialization function and decremented in the termination function. The module is really uninitialized only after the counter drops back down to zero.

Note that if you are using MCTRL.DLL from your dynamic library, you may not call the initialization and termination functions in context of DllMain(). Windows severly limits what can be done safely in the DllMain() context. Even if it would be safe for some modules currently there is no guaranty that future version of mCtrl won't use anything problematic in this regard.

About Message Constants

mCtrl makes this promise (valid also for future versions of MCTRL.DLL): All mCtrl controls only implement private messages in the range 0x0401 (WM_USER + 1) to 0x1299 (WM_USER + 0x0eff).

Beside that mCtrl controls support some common control general messages (CCM_xxxx which start at 0x2000; e.g. CCM_SETUNICODEFORMAT).

I.e., if an application implements some custom control as a subclass of mCtrl control, it should acquire its private message from the range 0x1300 to 0x1fff.

About Multi-threading

mCtrl is designed to be multi-threading friendly. In general, all functions are reentrant. I.e. you can call the same MCTRL.DLL function concurrently from multiple threads.

However remember that access to data visible externally through MCTRL.DLL interface is not synchronized: If you have such data (e.g. MC_HVALUE or MC_HTABLE and then want to manipulate with the data concurrently from multiple threads, MCTRL.DLL does not synchronize for you: It's application developer's to do so in order to avoid race conditions.

Also note that some mCtrl modules may include yet another limitations. Any such limitations are described in documentation of such the particular modules. (The MC_WC_HTML control is a prominent example of such limitation.)

DLL Dependencies

The policy for mCtrl is to make hard dependencies only on DLLs available on on all supported Windows versions. Some features may depend on existence of newer or optional DLLs.

In particular, all controls may use visual styles (UXTHEME.DLL) when system supports it.

Also note that chart control (mCtrl/chart.h) and image view control (mCtrl/imgview.h) require GDI+ (GDIPLUS.DLL) for its functioning. This library is available standardly on Windows XP and newer. Plain Windows 2000, without any service pack, are not equipped with it. However Microsoft has released distributable version of GDIPLUS.DLL: If your application relies on this control, and you want to support Windows 2000, you should distribute the GDIPLUS.DLL with it.