Get started with C++/WinRT

To get you up to speed with using C++/WinRT, this topic walks through a simple code example based on a new Windows Console Application (C++/WinRT) project. This topic also shows how to add C++/WinRT support to a Windows Desktop application project.

Note

While we recommend that you develop with the latest versions of Visual Studio and the Windows SDK, if you're using Visual Studio 2017 (version 15.8.0 or higher), and targeting the Windows SDK version 10.0.17134.0 (Windows 10, version 1803), then a newly created C++/WinRT project may fail to compile with the error "error C3861: 'from_abi': identifier not found", and with other errors originating in base.h. The solution is to either target a later (more conformant) version of the Windows SDK, or set project property C/C++ > Language > Conformance mode: No (also, if /permissive- appears in project property C/C++ > Language > Command Line under Additional Options, then delete it).

A C++/WinRT quick-start

Note

For info about setting up Visual Studio for C++/WinRT development—including installing and using the C++/WinRT Visual Studio Extension (VSIX) and the NuGet package (which together provide project template and build support)—see Visual Studio support for C++/WinRT.

Create a new Windows Console Application (C++/WinRT) project.

Edit pch.h and main.cpp to look like this.

// pch.h
#pragma once
#include <winrt/Windows.Foundation.Collections.h>
#include <winrt/Windows.Web.Syndication.h>
#include <iostream>
// main.cpp
#include "pch.h"

using namespace winrt;
using namespace Windows::Foundation;
using namespace Windows::Web::Syndication;

int main()
{
    winrt::init_apartment();

    Uri rssFeedUri{ L"https://blogs.windows.com/feed" };
    SyndicationClient syndicationClient;
    SyndicationFeed syndicationFeed = syndicationClient.RetrieveFeedAsync(rssFeedUri).get();
    for (const SyndicationItem syndicationItem : syndicationFeed.Items())
    {
        winrt::hstring titleAsHstring = syndicationItem.Title().Text();
        std::wcout << titleAsHstring.c_str() << std::endl;
    }
}

Let's take the short code example above piece by piece, and explain what's going on in each part.

#include <winrt/Windows.Foundation.Collections.h>
#include <winrt/Windows.Web.Syndication.h>

With the default project settings, the included headers come from the Windows SDK, inside the folder%WindowsSdkDir%Include<WindowsTargetPlatformVersion>\cppwinrt\winrt. Visual Studio includes that path in its IncludePath macro. But there's no strict dependency on the Windows SDK, because your project (via the cppwinrt.exe tool) generates those same headers into your project's $(GeneratedFilesDir) folder. They'll be loaded from that folder if they can't be found elsewhere, or if you change your project settings.

The headers contain Windows APIs projected into C++/WinRT. In other words, for each Windows type, C++/WinRT defines a C++-friendly equivalent (called the projected type). A projected type has the same fully-qualified name as the Windows type, but it's placed in the C++ winrt namespace. Putting these includes in your precompiled header reduces incremental build times.

Important

Whenever you want to use a type from a Windows namespaces, include the corresponding C++/WinRT Windows namespace header file, as shown above. The corresponding header is the one with the same name as the type's namespace. For example, to use the C++/WinRT projection for the Windows::Foundation::Collections::PropertySet runtime class, #include <winrt/Windows.Foundation.Collections.h>. If you include winrt/Windows.Foundation.Collections.h, then you don't also need to include winrt/Windows.Foundation.h. Each C++/WinRT projection header automatically includes its parent namespace header file; so you don't need to explicitly include it. Although, if you do, there will be no error.

using namespace winrt;
using namespace Windows::Foundation;
using namespace Windows::Web::Syndication;

The using namespace directives are optional, but convenient. The pattern shown above for such directives (allowing unqualified name lookup for anything in the winrt namespace) is suitable for when you're beginning a new project and C++/WinRT is the only language projection you're using inside of that project. If, on the other hand, you're mixing C++/WinRT code with C++/CX and/or SDK application binary interface (ABI) code (you're either porting from, or interoperating with, one or both of those models), then see the topics Interop between C++/WinRT and C++/CX, Move to C++/WinRT from C++/CX, and Interop between C++/WinRT and the ABI.

winrt::init_apartment();

The call to winrt::init_apartment initializes the thread in the Windows Runtime; by default, in a multithreaded apartment. The call also initializes COM.

Uri rssFeedUri{ L"https://blogs.windows.com/feed" };
SyndicationClient syndicationClient;

Stack-allocate two objects: they represent the uri of the Windows blog, and a syndication client. We construct the uri with a simple wide string literal (see String handling in C++/WinRT for more ways you can work with strings).

SyndicationFeed syndicationFeed = syndicationClient.RetrieveFeedAsync(rssFeedUri).get();

SyndicationClient::RetrieveFeedAsync is an example of an asynchronous Windows Runtime function. The code example receives an asynchronous operation object from RetrieveFeedAsync, and it calls get on that object to block the calling thread and wait for the result (which is a syndication feed, in this case). For more about concurrency, and for non-blocking techniques, see Concurrency and asynchronous operations with C++/WinRT.

for (const SyndicationItem syndicationItem : syndicationFeed.Items()) { ... }

SyndicationFeed.Items is a range, defined by the iterators returned from begin and end functions (or their constant, reverse, and constant-reverse variants). Because of this, you can enumerate Items with either a range-based for statement, or with the std::for_each template function. Whenever you iterate over a Windows Runtime collection like this, you'll need to #include <winrt/Windows.Foundation.Collections.h>.

winrt::hstring titleAsHstring = syndicationItem.Title().Text();
std::wcout << titleAsHstring.c_str() << std::endl;

Gets the feed's title text, as a winrt::hstring object (more details in String handling in C++/WinRT). The hstring is then output, via the c_str function, which reflects the pattern used with C++ Standard Library strings.

As you can see, C++/WinRT encourages modern, and class-like, C++ expressions such as syndicationItem.Title().Text(). This is a different, and cleaner, programming style from traditional COM programming. You don't need to directly initialize COM, work with COM pointers.

Nor do you need to handle HRESULT return codes. C++/WinRT converts error HRESULTs to exceptions such as winrt::hresult-error for a natural and modern programming style. For more info about error-handling, and code examples, see Error handling with C++/WinRT.

Modify a Windows Desktop application project to add C++/WinRT support

This section shows you how you can add C++/WinRT support to a Windows Desktop application project that you might have. If you don't have an existing Windows Desktop application project, then you can follow along with these steps by first creating one. For example, open Visual Studio and create a Visual C++ > Windows Desktop > Windows Desktop Application project.

You can optionally install the C++/WinRT Visual Studio Extension (VSIX) and the NuGet package. For details, see Visual Studio support for C++/WinRT.

Set project properties

Go to project property General > Windows SDK Version, and select All Configurations and All Platforms. Ensure that Windows SDK Version is set to 10.0.17134.0 (Windows 10, version 1803) or greater.

Confirm that you're not affected by Why won't my new project compile?.

Because C++/WinRT uses features from the C++17 standard, set project property C/C++ > Language > C++ Language Standard to ISO C++17 Standard (/std:c++17).

The precompiled header

The default project template creates a precompiled header for you, named either framework.h, or stdafx.h. Rename that to pch.h. If you have a stdafx.cpp file, then rename that to pch.cpp. Set project property C/C++ > Precompiled Headers > Precompiled Header to Create (/Yc), and Precompiled Header File to pch.h.

Find and replace all #include "framework.h" (or #include "stdafx.h") with #include "pch.h".

In pch.h, include winrt/base.h.

// pch.h
...
#include <winrt/base.h>

Linking

The C++/WinRT language projection depends on certain Windows Runtime free (non-member) functions, and entry points, that require linking to the WindowsApp.lib umbrella library. This section describes three ways of satisfying the linker.

The first option is to add to your Visual Studio project all of the C++/WinRT MSBuild properties and targets. To do this, install the Microsoft.Windows.CppWinRT NuGet package into your project. Open the project in Visual Studio, click Project > Manage NuGet Packages... > Browse, type or paste Microsoft.Windows.CppWinRT in the search box, select the item in search results, and then click Install to install the package for that project.

You can also use project link settings to explicitly link WindowsApp.lib. Or, you can do it in source code (in pch.h, for example) like this.

#pragma comment(lib, "windowsapp")

You can now compile and link, and add C++/WinRT code to your project (for example, code similar to that shown in the A C++/WinRT quick-start section, above).

The three main scenarios for C++/WinRT

As you use and become familiar with C++/WinRT, and work through the rest of the documentation here, you'll likely notice that there are three main scenarios, as described in the following sections.

Consuming Windows Runtime APIs and types

In other words, using, or calling APIs. For example, making API calls to communicate using Bluetooth; to stream and present video; to integrate with the Windows shell; and so on. C++/WinRT fully and uncompromisingly supports this category of scenario. For more info, see Consume APIs with C++/WinRT.

Authoring Windows Runtime APIs and types

In other words, producing APIs and types. For example, producing the kinds of APIs described in the section above; or the graphics APIs; the storage and file system APIs; the networking APIs, and so on. For more info, see Author APIs with C++/WinRT.

Authoring APIs with C++/WinRT is a little more involved than consuming them, because you must use IDL to define the shape of the API before you can implement it. There's a walkthrough of doing that in XAML controls; bind to a C++/WinRT property.

XAML applications

This scenario is about building applications and controls on the XAML UI framework. Working in a XAML application amounts to a combination of consuming and authoring. But since XAML is the dominant UI framework on Windows today, and its influence over the Windows Runtime is proportionate to that, it deserves its own category of scenario.

Be aware that XAML works best with programming languages that offer reflection. In C++/WinRT, you sometimes have to do a little extra work in order to interoperate with the XAML framework. All of those cases are covered in the documentation. Good places to start are XAML controls; bind to a C++/WinRT property and XAML custom (templated) controls with C++/WinRT.

Important APIs