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This tutorial uses C++/CX. Microsoft has released C++/WinRT: an entirely standard modern C++17 language projection for Windows Runtime (WinRT) APIs. For more information on this language, please see C++/WinRT.
With Microsoft Visual Studio, you can use C++/CX to develop an app that runs on Windows 10 with a UI that's defined in Extensible Application Markup Language (XAML).
This tutorial uses Visual Studio Community 2019. If you are using a different version of Visual Studio, it may look a little different for you.
It is possible to compile C programs with it, but you'll see some issues and incompleteness.Moreover, it lacks many features familiar with more modern IDEs. For that reason, the tools included - notably the compiler and debugger - are slightly obsolete.Plus, the latest versions were released before the newest version of C of 2017, so it's lagging.
If you're coming from a background in Windows desktop programming in C++, you'll probably find that some aspects of writing apps for the UWP are familiar, but other aspects require some learning.
You can use the STL, the CRT (with some exceptions), and any other C++ library as long as the code only calls Windows functions that are accessible from the Windows Runtime environment.
If you're accustomed to visual designers, you can still use the designer built into Microsoft Visual Studio, or you can use the more full-featured Blend for Visual Studio. If you're accustomed to coding UI by hand, you can hand-code your XAML.
You're still creating apps that use Windows operating system types and your own custom types.
You're still using the Visual Studio debugger, profiler, and other development tools.
You're still creating apps that are compiled to native machine code by the Visual C++ compiler. UWP apps in C++/CX don't execute in a managed runtime environment.
The design principles for UWP apps and Universal Windows apps are very different from those for desktop apps. Window borders, labels, dialog boxes, and so on, are de-emphasized. Content is foremost. Great Universal Windows apps incorporate these principles from the very beginning of the planning stage.
You're using XAML to define the entire UI. The separation between UI and core program logic is much clearer in a Windows Universal app than in an MFC or Win32 app. Other people can work on the appearance of the UI in the XAML file while you're working on the behavior in the code file.
You're primarily programming against a new, easy-to-navigate, object-oriented API, the Windows Runtime, although on Windows devices Win32 is still available for some functionality.
You use C++/CX to consume and create Windows Runtime objects. C++/CX enables C++ exception handling, delegates, events, and automatic reference counting of dynamically created objects. When you use C++/CX, the details of the underlying COM and Windows architecture are hidden from your app code. For more information, see C++/CX Language Reference.
Your app is compiled into a package that also contains metadata about the types that your app contains, the resources that it uses, and the capabilities that it requires (file access, internet access, camera access, and so forth).
In the Microsoft Store and Windows Phone Store your app is verified as safe by a certification process and made discoverable to millions of potential customers.
Our first app is a 'Hello World' that demonstrates some basic features of interactivity, layout, and styles. We'll create an app from the Windows Universal app project template. If you've developed apps for Windows 8.1 and Windows Phone 8.1 before, you might remember that you had to have three projects in Visual Studio, one for the Windows app, one for the phone app, and another with shared code. The Windows 10 Universal Windows Platform (UWP) makes it possible to have just one project, which runs on all devices, including desktop and laptop computers running Windows 10, devices such as tablets, mobile phones, VR devices and so on.
We'll start with the basics:
How to create a Universal Windows project in Visual Studio.
How to understand the projects and files that are created.
How to understand the extensions in Visual C++ component extensions (C++/CX), and when to use them.
First, create a solution in Visual Studio
In Visual Studio, on the menu bar, choose File > New > Project...
In the Create a new project dialog box, select Blank App (Universal Windows - C++/CX). If you don't see this option, make sure you have the Universal Windows App Development Tools installed. See Get set up for more information.
Choose Next, and then enter a name for the project. We'll name it HelloWorld.
Choose the Create button.
If this is the first time you have used Visual Studio, you might see a Settings dialog asking you to enable Developer mode. Developer mode is a special setting that enables certain features, such as permission to run apps directly, rather than only from the Store. For more information, please read Enable your device for development. To continue with this guide, select Developer mode, click Yes, and close the dialog.
Your project files are created.
Before we go on, let's look at what's in the solution.
Every .xaml file in a project folder has a corresponding .xaml.h file and .xaml.cpp file in the same folder and a .g file and a .g.hpp file in the Generated Files folder, which is on disk but not part of the project. You modify the XAML files to create UI elements and connect them to data sources (DataBinding). You modify the .h and .cpp files to add custom logic for event handlers. The auto-generated files represent the transformation of the XAML markup into C++/CX. Don't modify these files, but you can study them to better understand how the code-behind works. Basically, the generated file contains a partial class definition for a XAML root element; this class is the same class that you modify in the *.xaml.h and .cpp files. The generated files declare the XAML UI child elements as class members so that you can reference them in the code you write. At build time, the generated code and your code are merged into a complete class definition and then compiled.
Let's look first at the project files.
If you examine the code in App.xaml.h, App.xaml.cpp in the shared project, you'll notice that it's mostly C++ code that looks familiar. However, some syntax elements might not be as familiar if you are new to Windows Runtime apps, or you've worked with C++/CLI. Here are the most common non-standard syntax elements you'll see in C++/CX:
Almost all Windows Runtime classes, which includes all the types in the Windows API--XAML controls, the pages in your app, the App class itself, all device and network objects, all container types--are declared as a ref class. (A few Windows types are value class or value struct). A ref class is consumable from any language. In C++/CX, the lifetime of these types is governed by automatic reference counting (not garbage collection) so that you never explicitly delete these objects. You can create your own ref classes as well.
ref new and ^ (hats)
You declare a variable of a ref class by using the ^ (hat) operator, and you instantiate the object with the ref new keyword. Thereafter you access the object's instance methods with the -> operator just like a C++ pointer. Static methods are accessed with the :: operator just as in ISO C++.
In the following code, we use the fully qualified name to instantiate an object, and use the -> operator to call an instance method.
Typically, in a .cpp file we would add a
using namespace Windows::UI::Xaml::Media::Imaging directive and the auto keyword, so that the same code would look like this:
A ref class can have properties, which, just as in managed languages, are special member functions that appear as fields to consuming code.
Just as in managed languages, a delegate is a reference type that encapsulates a function with a specific signature. They are most often used with events and event handlers
Let's add some content to the app.
Step 1: Modify your start page
In Solution Explorer, open MainPage.xaml.
Create controls for the UI by adding the following XAML to the root Grid, immediately before its closing tag. It contains a StackPanel that has a TextBlock that asks the user's name, a TextBox element that accepts the user's name, a Button, and another TextBlock element.
At this point, you have created a very basic Universal Windows app. To see what the UWP app looks like, press F5 to build, deploy, and run the app in debugging mode.
The default splash screen appears first. It has an image—AssetsSplashScreen.scale-100.png—and a background color that are specified in the app's manifest file. To learn how to customize the splash screen, see Adding a splash screen.
When the splash screen disappears, your app appears. It displays the main page of the App.
It doesn't do much—yet—but congratulations, you've built your first Universal Windows Platform app!
To stop debugging and close the app, return to Visual Studio and press Shift+F5.
For more information, see Run a Store app from Visual Studio.
In the app, you can type in the TextBox, but clicking the Button doesn't do anything. In later steps, you create an event handler for the button's Click event, which displays a personalized greeting.
In MainPage.xaml, in either XAML or design view, select the 'Say Hello' Button in the StackPanel you added earlier.
Open the Properties Window by pressing F4, and then choose the Events button ().
Find the Click event. In its text box, type the name of the function that handles the Click event. For this example, type 'Button_Click'.
Press Enter. The event handler method is created in MainPage.xaml.cpp and opened so that you can add the code that's executed when the event occurs.
At the same time, in MainPage.xaml, the XAML for the Button is updated to declare the Click event handler, like this:
You could also have simply added this to the xaml code manually, which can be helpful if the designer doesn't load. If you enter this manually, type 'Click' and then let IntelliSense pop up the option to add a new event handler. That way, Visual Studio creates the necessary method declaration and stub.
The designer fails to load if an unhandled exception occurs during rendering. Rendering in the designer involves running a design-time version of the page. It can be helpful to disable running user code. You can do this by changing the setting in the Tools, Options dialog box. Under XAML Designer, uncheck Run project code in XAML designer (if supported).
In MainPage.xaml.cpp, add the following code to the Button_Click event handler that you just created. This code retrieves the user's name from the
nameInputTextBox control and uses it to create a greeting. The
greetingOutputTextBlock displays the result.
Set the project as the startup, and then press F5 to build and run the app. When you type a name in the text box and click the button, the app displays a personalized greeting.
It's easy to customize the look and feel of your app. By default, your app uses resources that have a light style. The system resources also include a light theme. Let's try it out and see what it looks like.
To switch to the dark theme
In the opening Application tag, edit the RequestedTheme property and set its value to Dark:
Here's the full Application tag with the dark theme :
Press F5 to build and run it. Notice that it uses the dark theme.
Which theme should you use? Whichever one you want. Here's our take: for apps that mostly display images or video, we recommend the dark theme; for apps that contain a lot of text, we recommend the light theme. If you're using a custom color scheme, use the theme that goes best with your app's look and feel. In the rest of this tutorial, we use the Light theme in screenshots.
Note The theme is applied when the app is started and can't be changed while the app is running.
Right now, in the Windows app the text is very small and difficult to read. Let's fix that by applying a system style.
To change the style of an element
In the Windows project, open MainPage.xaml.
In either XAML or design view, select the 'What's your name?'TextBlock that you added earlier.
In the Properties window (F4), choose the Properties button () in the upper right.
Expand the Text group and set the font size to 18 px.
Expand the Miscellaneous group and find the Style property.
Click the property marker (the green box to the right of the Style property), and then, on the menu, choose System Resource > BaseTextBlockStyle.
BaseTextBlockStyle is a resource that's defined in the ResourceDictionary in
On the XAML design surface, the appearance of the text changes. In the XAML editor, the XAML for the TextBlock is updated:
Repeat the process to set the font size and assign the BaseTextBlockStyle to the
Tip Although there's no text in this TextBlock, when you move the pointer over the XAML design surface, a blue outline shows where it is so that you can select it.
Your XAML now looks like this:
Press F5 to build and run the app. It now looks like this:
Now we'll make the UI adapt to different screen sizes so it looks good on mobile devices. To do this, you add a VisualStateManager and set properties that are applied for different visual states.
To adjust the UI layout
In the XAML editor, add this block of XAML after the opening tag of the root Grid element.
Debug the app on the local machine. Notice that the UI looks the same as before unless the window gets narrower than 641 device-independent pixels (DIPs).
Debug the app on the mobile device emulator. Notice that the UI uses the properties you defined in the
narrowState and appears correctly on the small screen.
If you've used a VisualStateManager in previous versions of XAML, you might notice that the XAML here uses a simplified syntax.
The VisualState named
wideState has an AdaptiveTrigger with its MinWindowWidth property set to 641. This means that the state is to be applied only when the window width is not less than the minimum of 641 DIPs. You don't define any Setter objects for this state, so it uses the layout properties you defined in the XAML for the page content.
The second VisualState,
narrowState, has an AdaptiveTrigger with its MinWindowWidth property set to 0. This state is applied when the window width is greater than 0, but less than 641 DIPs. (At 641 DIPs, the
wideState is applied.) In this state, you do define some Setter objects to change the layout properties of controls in the UI:
contentPanelelement from 120 to 20.
inputPanelelement from Horizontal to Vertical.
Congratulations, you've completed the first tutorial! It taught how to add content to Windows Universal apps, how to add interactivity to them, and how to change their appearance.
If you have a Windows Universal app project that targets Windows 8.1 and/or Windows Phone 8.1, you can port it to Windows 10. There is no automatic process for this, but you can do it manually. Start with a new Windows Universal project to get the latest project system structure and manifest files, copy your code files into the project's directory structure, add the items to your project, and rewrite your XAML using the VisualStateManager according to the guidance in this topic. For more information, see Porting a Windows Runtime 8 project to a Universal Windows Platform (UWP) project and Porting to the Universal Windows Platform (C++).
If you have existing C++ code that you want to integrate with a UWP app, such as to create a new UWP UI for an existing application, see How to: Use existing C++ code in a Universal Windows project.C++ provides the following classes to perform output and input of characters to/from files:
ofstream: Stream class to write on files
ifstream: Stream class to read from files
fstream: Stream class to both read and write from/to files.
ostream. We have already used objects whose types were these classes:
cinis an object of class
coutis an object of class
ostream. Therefore, we have already been using classes that are related to our file streams. And in fact, we can use our file streams the same way we are already used to use
cout, with the only difference that we have to associate these streams with physical files. Let's see an example:
example.txtand inserts a sentence into it in the same way we are used to do with
cout, but using the file stream
myfile) and any input or output operation performed on this stream object will be applied to the physical file associated to it.
open (filename, mode);
filenameis a string representing the name of the file to be opened, and
modeis an optional parameter with a combination of the following flags:
|Open for input operations.|
|Open for output operations.|
|Open in binary mode.|
|Set the initial position at the end of the file.|
If this flag is not set, the initial position is the beginning of the file.
|All output operations are performed at the end of the file, appending the content to the current content of the file.|
|If the file is opened for output operations and it already existed, its previous content is deleted and replaced by the new one.|
). For example, if we want to open the file
example.binin binary mode to add data we could do it by the following call to member function
openmember functions of classes
fstreamhas a default mode that is used if the file is opened without a second argument:
|class||default mode parameter|
ios::outare automatically and respectively assumed, even if a mode that does not include them is passed as second argument to the
openmember function (the flags are combined).
fstream, the default value is only applied if the function is called without specifying any value for the mode parameter. If the function is called with any value in that parameter the default mode is overridden, not combined.
myfileobject and conduct the same opening operation in our previous example by writing:
is_open. This member function returns a
truein the case that indeed the stream object is associated with an open file, or
close. This member function takes flushes the associated buffers and closes the file:
ios::binaryflag is not included in their opening mode. These files are designed to store text and thus all values that are input or output from/to them can suffer some formatting transformations, which do not necessarily correspond to their literal binary value.
trueif the stream is ready for more operations, and
falseif either the end of the file has been reached or if some other error occurred.
trueif a reading or writing operation fails. For example, in the case that we try to write to a file that is not open for writing or if the device where we try to write has no space left.
truein the same cases as
bad(), but also in the case that a format error happens, like when an alphabetical character is extracted when we are trying to read an integer number.
trueif a file open for reading has reached the end.
falsein the same cases in which calling any of the previous functions would return
true. Note that
badare not exact opposites (
goodchecks more state flags at once).
clear()can be used to reset the state flags.
istream, keeps an internal get position with the location of the element to be read in the next input operation.
ostream, keeps an internal put position with the location where the next element has to be written.
fstream, keeps both, the get and the put position, like
streampos, which is a type representing the current get position (in the case of
tellg) or the put position (in the case of
seekg ( position );
seekp ( position );
position(counting from the beginning of the file). The type for this parameter is
streampos, which is the same type as returned by functions
seekg ( offset, direction );
seekp ( offset, direction );
offsetis of type
directionis of type
seekdir, which is an enumerated type that determines the point from where offset is counted from, and that can take any of the following values:
|offset counted from the beginning of the stream|
|offset counted from the current position|
|offset counted from the end of the stream|
streamposis a specific type used for buffer and file positioning and is the type returned by
file.tellg(). Values of this type can safely be subtracted from other values of the same type, and can also be converted to an integer type large enough to contain the size of the file.
streamoff. These types are also defined as member types of the stream class:
|Defined as |
It can be converted to/from
|It is an alias of one of the fundamental integral types (such as |
>>) and functions like
getlineis not efficient, since we do not need to format any data and data is likely not formatted in lines.
read. The first one (
write) is a member function of
readis a member function of
ifstream). Objects of class
fstreamhave both. Their prototypes are:
memory_blockis of type
char), and represents the address of an array of bytes where the read data elements are stored or from where the data elements to be written are taken. The
sizeparameter is an integer value that specifies the number of characters to be read or written from/to the memory block.
ios::ateflag, which means that the get pointer will be positioned at the end of the file. This way, when we call to member
tellg(), we will directly obtain the size of the file.
ofstream, each time the member function
put(which writes a single character) is called, the character may be inserted in this intermediate buffer instead of being written directly to the physical file with which the stream is associated.
sync()causes an immediate synchronization. This function returns an
intvalue equal to -1 if the stream has no associated buffer or in case of failure. Otherwise (if the stream buffer was successfully synchronized) it returns