I'm coming from C# background, learning C++, specifically on the Windows Phone 8 platform.
Many code samples (installed with the SDK) show usage of the Hat operator ^ (Reference here: Types that wear hats).
For example:
void PhoneDX::Initialize(CoreApplicationView^ applicationView)
{
// ... function body
}
I am wondering:
Why are most of the pointers being defined in that manner, specifically on Windows Phone 8 ?
Is that syntax mandatory? Suppose i am using a C++ native library from another platform (that doesn't use this syntax). Should it work with no issues?
A hat is a compiler-supported smart pointer type that is designed to make Windows Runtime types easier to work with from C++ code. As discussed in "Types That Wear Hats" and the other articles in that series, the C++/CX language extensions are optional: any code that can be written using C++/CX can be written in C++ without using the language extensions, albeit at greater code complexity and verbosity.
The key here is that hats are designed to facilitate code that makes use of Windows Runtime types. In general, you should confine your use of C++/CX and Windows Runtime types to the boundary of your components: most of your code should be standard, portable, normal C++ code. C++/CX should be used (1) to wrap C++ code to make it consumable through the Windows Runtime and (2) to use other Windows Runtime components from your component.
So, yes, the syntax is optional, but you should strongly consider using it when writing code that must work with Windows Runtime types. You should be able to use any ordinary C++ code, without modification, with the caveat that Windows Store apps and Windows Phone apps run with low privileges and some facilities are not available (e.g., there is no console, so console I/O doesn't work, and the runtime provides specialized process lifetime management facilities, so calling exit is a bad idea).
You might have a harder time grasping it since it's somewhat of a compound leap from (1) C# references to (4) C++/CX hats, with a stop in the middle for (2) C++ pointers then (3) reference counted objects.
The ^ smart pointers are a language extension, not part of standard C++, for handling the Windows Runtime types (which are reference counted)
so answering your points:
If you're seeing them a lot with Windows Phone 8, it's because ^ is used for Windows Runtime types, which would be used a lot in that platform samples (since the samples are trying to demonstrate that platform's api and features).
You would need to use conventions for that library, which would probably require that you use the types it defines (if it has its own smart pointers) or standard/regular pointers (i.e. *) or Standard Library smart pointers (i.e. shared_ptr).
Some concepts that should help you understanding this would be the lifetime of C++ objects, deterministic destruction (vs. waiting for a garbage collector to kick in), reference counting, stack/static vs. heap/dynamic allocation of objects.
Related
I understand how COM can achieve compiler agnostic C++ code, since it defines an ABI by being careful what features of the C++ language to use. It's just C++ code talking to C++ code in a really clever way. However I still don't understand how it can allow for language interop with C# or Javascript for example.
Where is the boundary? The only explanation I have right now is that the language compiler itself must have special support for COM so that it can generate the proper assembly code to allow for accurate communication between caller/callees.
Since you've tagged your question with WinRT, I assume you're asking specifically about how this is achieved by WinRT language projections. In that case, all languages must have some way to map their natural language constructs to the COM ABI that WinRT defines. That ABI is derived from metadata encoded in the ECMA 335 standard and special rules are applied to transform the abstract metadata into a concrete ABI. There are naturally different ways to achieve this. The CLR itself was updated to support WinRT in C#. The Visual C++ compiler was (sadly) updated with language extensions to support WinRT via C++/CX. The C++/WinRT approach is very different in that it requires only a standard C++ compiler and all of the knowledge about WinRT is delivered via a standard C++ header-only library. Other languages might take different approaches, but at the end of the day they must agree on the way that types expressed in metadata are transformed into objects and virtual function calls on the ABI based on COM.
And while this process is not well documented at the moment, C++/WinRT is one of the only open source language projections and thus acts as a useful reference implementation for those who need to understand how WinRT works under the hood.
https://github.com/microsoft/cppwinrt
The "Type Library" is what enables interop of COM components between different languages.
https://learn.microsoft.com/en-us/windows/desktop/midl/com-dcom-and-type-libraries
A type library (.tlb) is a binary file that stores information about a
COM or DCOM object's properties and methods in a form that is
accessible to other applications at runtime. Using a type library, an
application or browser can determine which interfaces an object
supports, and invoke an object's interface methods. This can occur
even if the object and client applications were written in different
programming languages. The COM/DCOM run-time environment can also use
a type library to provide automatic cross-apartment, cross-process,
and cross-machine marshaling for interfaces described in type
libraries.
The other approach for language interop (e.g. C++ projecting objects to Javascript) is that a COM object can implement IDispatch.
It’s not magic, of course.
COM sets up rules for language interop. It’s just a contract, with some helpful tooling. Each language that wants to support COM has to find a way to abide by the rules on its own. They all have to provide their own compatible mechanism one way or another.
In the case of C++, the rules appear to come for free as you mentioned, but be aware there is one caveat: the language standard does not specify the layout and mechanism of classes and virtual functions. The method mimicked by COM is one extremely common implementation of virtual calling (“the VTable”), and COM follows the exact layout used by the Microsoft compiler. But you can have a perfectly valid C++ compiler where classes with virtual functions would not be compatible with the COM layout. It’s just that nobody does that, at least not in Windows compilers. So even in C++ there is some “meeting in the middle” by the compiler.
In C, you have to do the whole thing by hand. Other languages might allow you to do the same thing (assembler of course).
To help compiled languages exchange information about specific contracts, COM provides Type Libraries and mechanisms to read them. A compiler or language that want to take advantage of them also has to “meet in the middle” and learn how to process them (for example, the Microsoft C++ #import directive; the VB6 Libraries menu).
No every language will support everything you can do in COM, because there is a point (in more obscure features) where the return on investment in implementing support in the language doesn’t pan out. Each language has to pick its own limitations. There is plenty of stuff that you can do in COM (read the IDL specs) that VB6 cannot do.
Because following COM rules in a script-like language is between inpractical and impossible, COM offers a higher-level approach (Automation) that is more amenable to dynamic languages, even if more limited. But a language implementer that wants to provide client support for Automation has to implement an understanding of the IDispatch interface, an activation mechanism, and a translation to its language’s proper facilities. And a scripting language wanting to provide support for creating COM servers has to work even harder to implement a valid COM IDispatch implementation and a standalone host engine on behalf of the user scripts. Even VBScript couldn’t do this at the beginning, until Microsoft added .SCR support with the Windows Scripting Host. “Meeting in the middle” again.
If a language wants to support both pure COM and Automation, they need to work double hard; support for one does not automatically give you support for the other.
For .NET languages like C#, most of the work is done for both native COM and Automation inside of the .NET Runtime, which provides the implementation of the COM Callable Wrappers (CCW) and Runtime Callable Wrappers (RCW) necessary to interact with COM, and handling the conflicts between the Reference Count approach of COM and the GC approach of .NET. Microsoft did all the work in one place so individual .NET language designers didn’t have to.
So, yes, the language implementer has to work extra to give the language special support for COM: following the binary layout rules, implementing a translation layer when needed, and/or possibly providing tooling to read Type Libraries.
Language Interop requires both sides (the caller and the callee) to “meet in the middle” somewhere. COM is just a specification that gives designers that middle ground, “a place where all can meet”.
We have a program written in VBA that is running on Windows machines.
We have a very similar program written in ANSI C, using a Keil IDE and compiler that is running on an STR9x uP.
Our plans were to rewrite the VBA code in .NET using C#.
What is the feasibility of writing the shared code in C++ to be used on both systems? Obviously, the .NET framework would be off limits, but that isn't much of a concern. I'm wondering, specifically, about how labor intensive you think the compilation process might be.
This is kind of a theoretical question, I know, but thanks for any thoughts.
I do this a as general practice. I think a better question than "is it possible" is "how should I structure my code to be able to run on both an embedded system and also a PC".
I prefer to write the code in C and structure each file as a c++ class using static variables to make global variables private to the module. Create getter and setter functions to access the private variables. Also use function pointers which I set at initialization of the module for the methods the module need to call outside of the module.
It is also easy to refactor from the above structured c code to a class in c# or c++.
You can also use C++ directly but using it incorrectly on an embedded system can cause problems.
You will need a hardware abstraction layer if you are accessing any hardware. I separate my code into two types the first being code that has no reference to what it is running on and other code which I refer to as drivers.
I use this code for reusing modules for things like communication protocols. But more importantly I use it for testing. I like to use gtest to unit test the modules. I can also rewrite the drivers and simulate the hardware on a PC to be able to run it on the PC.
Obviously, the .NET framework would be off limits
Not necessarily true. Given sufficient ROM and RAM resources (256K/64K respectively), the .NET Micro Framework will run on your device. However that is not necessarily a good reason to use it; there are already two other commonly used portable languages available for both your embedded target and Windows: C and C++. The target resource required for both C and C++ is minimal - C/C++ runtime start-up code can be well under 1K of code, almost all available resources can be utilised by your application code rather than the run-time environment.
The trick to utilising common code on both platforms is abstraction. This will involve at least hardware abstraction and possibly OS abstraction if your target is using any sort of kernel or scheduler such as an RTOS or thread library.
I'd recommend designing your embedded target with a layer architecture, having at least a device layer and an application layer and as mentioned already, possibly a system layer that deals with IPC, synchronisation and scheduling, if used. You may have other higher layer interfaces such as networking or filesystem that would equally benefit from abstraction. Note that standard APIs such as BSD sockets or stdio already count as abstraction, so if your target uses these, you have less work to do in Windows (minor differences between BSD Sockets and Winsock may still need some work)
The application layer will have no OS or hardware dependencies other than those accessible through the device and system layers. You must then implement the device and system layers on Windows as either a simulation or remapping to services or devices available on Windows. Some RTOS's already include Windows simulators for test and development, but defining your own OS API layer that you can port between a number of native RTOS and GPOS will allow your application code to be ported to different targets for both simulation and real-time execution very quickly.
Where the platform differences are minor and localised, and may not justify an abstraction layer, then target specific conditional compilation may be appropriate. Compilers support predefined macros for architecture, OS or compiler specific code that can be used for both this localised code and to make the abstraction layer code itself common where there is significant similarity.
I want to use "printf" in driver code (DDK), therefore I've included stdio.h. But the compiler says:
error LNK2001: unresolved external symbol __imp__printf
Any ideas? I seen somewhere that it is not possible - but that's awful - I can't believe it. Why can't I use standard C routines in kernel code?
C functions like printf come from a static cstd.lib or something AFAIK don't they?
Why would WDK provide me with stdio.h then?
The Windows kernel only supports part of the standard C runtime. In particular, high-level functionality — like file streams, console I/O, and networking — is not supported. Instead, you need to use native kernel APIs for similar functionality.
The reason that stdio.h is included with the WDK is because some parts of the C runtime are provided for your convenience. For example, you can use memcmp (although the native RtlCompareMemory is preferred). Microsoft has not picked through the CRT headers to #ifdef out the bits and pieces that are not available in kernel mode. Once you develop some experience writing kernel drivers, you'll get the hang of what's possible in the kernel, and what probably won't work.
To address your high-level question: you're probably looking for some debug/logging mechanism. You really have two options:
DbgPrintEx is the easiest to use. It's basically a drop-in for printf (although you need to be careful about certain types of string inserts when running >=DISPATCH_LEVEL). Output goes to the debugger, or, if you like, to DbgView.
WPP is the industrial-strength option. The initial learning curve is pretty steep (although there are samples in the WDK). However, it is very flexible (e.g., you can create your own shrieks, like Print("My IP address is: %!IPV4!", ip);), and it is very fast (Microsoft ships WPP tracing in the non-debug builds of most Windows components).
Are they standard code c or c++ code? what are they?
The original Win32 API is C-based. There are however a substantial number of services within Windows that are COM based. Good examples are the clipboard, drag+drop, the shell, the user mode driver framework, DirectX. While it is technically possible to write COM code in C, it is excruciatingly painful to do so.
Realistically you use C++ there. And a C++ class library to make the original C-based API less painful, especially for GUI code.
They're standard C code, if you're programming against pure Windows API.
A C++ based wrapper called MFC is available.
All of this is being pushed out in favor of .NET framework.
The standard Windows API is a C library. Wrappers exist for other languages (C++, etc).
Just read it on wikipedia.
Windows API is langugage neutral. It is neither C nor C++. Microsoft says that Windows itself is written mainly in C++, but you don't need any classes for vast majority of the API and even classes in API (e.g. in Direct X) can be used in pure C without classes.
Although some C programmers think it is a C library, compiler of a programming language must support proprietary Windows calling model, it is not a classic C calling convention. (Obviously almost each real world C compiler supports it nowadays.)
Is there any fundamental differences in the WinAPI/Win32? Is there any additional knowledge required to take advantage of new OS features?
Are there any pitfalls which someone who's coded Win32 apps in the past might fall in?
I'm not talking about Silverlight, that's a whole different ball of wax. (I don't have the VS that supports that at work yet.)
Edit:
Drew has a pretty good answer so far, but what's critical for a programmer to know?
i.e. What should be in an appendix to Charles Petzold's book? (Theoretically)
There are of course lots of new APIs that you should be aware of to make sure you have the tools you need. Beyond that, there are some changes to note.
Philosophical changes
Large parts of the old win32 APIs focused on C-style APIs where handles were passed around. Nowadays, many of the new APIs being developed are COM-based, so boning up on COM and ATL would be worthwhile.
You might also want to take note of the new API style if you're writing your own libraries, which is a bit more consistent and avoids things like hungarian notation.
Replacements
Generally, don't assume that the methods you knew about 10 years ago are still state-of-the-art; they all still exist, so you won't necessarily be told you're doing it wrong. Check MSDN to see if it refers you to something better, and use the latest SDK so that you'll get deprecation warnings for some functions. Especially, make sure string functions you're using are secure.
Specifically, one 'replacement' API is Direct 2d, which is a DirectX-style API for UIs. If you're writing graphics code for Windows 7, you should consider Direct2d over GDI, which has a programming model that is compatible with, but very different than, GDI's. Direct 2d may be ported back to Vista.
Also, instead of using win32-style menuing, consider using the Ribbon, which will be available for Vista as well as Win7.
If you're using the common controls library, make sure to use v6, not the default of v5.
Finally, make sure you're not unnecessarily calling things that require admin privileges, as that will prompt UAC.
All I can think of for now.
There are new API's for each.
There is additional knowledge, though it may not be required, you should be familiar with 64-bit and multi-threaded application development to name a few. The higher level constructs such as Direct2D, .NET etc., etc., are what require the adjustment in knowledge, not necessarily the lower level APIs.
You have the choice: traditional C/C++ or use the newer .Net framework languages (C# / VB.net / Python.net and more). For the latter, knowing the framework is more important than the implementation. You're isolated (in general) from pointers, threading, buffers and memory management and apart from a few differences in syntax once you know the framework it's portable between languages (ie, you could easily pick up VB.net programming if you're a C# guy as most of what your apps will do is call parts of the framework). You can create a class in C#, use it in a VB.net program and reference the same class out of a Powershell cmdlet for example.
The old-style C interfaces are still for Win32 there but unless you've got a specific need to use them (legacy code, Direct X, device drivers for example) I'd look at the newer stuff. As for things like WPF, there isn't even a direct route in via unmanaged code - you have to jump through all sorts of ugly interop hoops.
Nothing special. The old stuff pretty much works as it did.
There are some new APIs, but nothing earth shattering (and following the old Win32 conventions).
So everything you know from Vista is still true for Win7.
Now, there are some new guidelines regarding user experience (touch screen, libraries (user experience stuff, not programmer stuff)), but the API style is the same.
Integrity levels are also a good thing to learn about. Depending on the nature of your application, if it attempts to do anything involving other processes that are running on the OS, it is important to know about this. This technology prevents processes at a lower integrity level from interacting with processes that are running at a higher integrity level. This includes messaging, hooks, DLL injection, opening handles, and many other techniques.