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#275 string interpolation tutorial for C# #1317
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#275 string interpolation tutorial for C#
mgroves 21354e7
#275 move code examples into snippets so they can be run by DocFx
mgroves 7a929b6
#275 corrects and fixes of string interpolation tutorial per review f…
mgroves ad9da53
#275 forgot namespace for CultureInfo
mgroves ba8c18b
#275 typo fix
mgroves a90ec1a
#275 remove intro header per recommendation
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--- | ||
title: String Interpolation | C# | ||
description: Learn how string interpolation works in C# 6 | ||
keywords: .NET, .NET Core, C#, string | ||
author: mgroves | ||
manager: BillWagner | ||
ms.date: 12/09/2016 | ||
ms.topic: article | ||
ms.prod: .net-core | ||
ms.technology: .net-core-technologies | ||
ms.devlang: csharp | ||
ms.assetid: f8806f6b-3ac7-4ee6-9b3e-c524d5301ae9 | ||
--- | ||
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# String Interpolation in C# | ||
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String Interpolation is the way that placeholders in a string are replaced by the value of a string variable. Before C# 6, the way to do this is with `System.String.Format`. This works okay, but since it uses numbered placeholders, it can be harder to read and more verbose. | ||
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Other programming languages have had string interpolation built into the language for a while. For instance, in PHP: | ||
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```PHP | ||
$name = "Jonas"; | ||
echo "My name is $name."; | ||
// This will output "My name is Jonas." | ||
``` | ||
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In C# 6, we finally have that style of string interpolation. You can use a `$` before a string to indicate that it should substitute variables/expressions for their values. | ||
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## Prerequisites | ||
You’ll need to setup your machine to run .NET core. You can find the | ||
installation instructions on the [.NET Core](https://www.microsoft.com/net/core) | ||
page. | ||
You can run this application on Windows, Ubuntu Linux, macOS or in a Docker container. | ||
You’ll need to install your favorite code editor. The descriptions below | ||
use [Visual Studio Code](https://code.visualstudio.com/) which is an open | ||
source, cross platform editor. However, you can use whatever tools you are | ||
comfortable with. | ||
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## Create the Application | ||
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Now that you've installed all the tools, create a new .NET Core | ||
application. To use the command line generator, execute the following command in your favorite shell: | ||
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`dotnet new` | ||
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This command will create a barebones .NET core project with `project.json` and `Program.cs` files. You will need to execute `dotnet restore` to restore the dependencies needed to compile this project. | ||
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To execute the program, use `dotnet run`. You should see "Hello, World" output to the console. | ||
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## Intro to String Interpolation | ||
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With `System.String.Format`, you would specify "placeholders" in a string that would be replaced by the parameters following the string. For instance: | ||
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[!code-csharp[String.Format example](../../../samples/snippets/csharp/new-in-6/string-interpolation.cs#StringFormatExample)] | ||
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That will output "My name is Matt Groves". | ||
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In C# 6, Instead of using String.Format, you can tell C# that a string is interpolated by prepending it with the `$` symbol, and then using the variables directly in the string. For instance: | ||
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[!code-csharp[Interpolation example](../../../samples/snippets/csharp/new-in-6/string-interpolation.cs#InterpolationExample)] | ||
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You don't have to use just variables. You can use any expression within the brackets. For instance: | ||
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[!code-csharp[Interpolation expression example](../../../samples/snippets/csharp/new-in-6/string-interpolation.cs#InterpolationExpressionExample)] | ||
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Which would output: | ||
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``` | ||
This is line number 1 | ||
This is line number 2 | ||
This is line number 3 | ||
This is line number 4 | ||
This is line number 5 | ||
``` | ||
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## How string interpolation works | ||
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Behind the scenes, this string interpolation syntax gets translated into String.Format by the compiler. So, you can do the [same type of stuff you've done before with String.Format](https://msdn.microsoft.com/en-us/library/dwhawy9k(v=vs.110).aspx). | ||
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For instance, you can add padding and numeric formatting: | ||
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[!code-csharp[Interpolation formatting example](../../../samples/snippets/csharp/new-in-6/string-interpolation.cs#InterpolationFormattingExample)] | ||
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The above would output something like: | ||
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``` | ||
998 5,177.67 | ||
999 6,719.30 | ||
1000 9,910.61 | ||
1001 529.34 | ||
1002 1,349.86 | ||
1003 2,660.82 | ||
1004 6,227.77 | ||
``` | ||
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If a variable name is not found, then a compile time error will be generated. | ||
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For instance: | ||
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```cs | ||
var animal = "fox"; | ||
var localizeMe = $"The {adj} brown {animal} jumped over the lazy {otheranimal}"; | ||
var adj = "quick"; | ||
Console.WriteLine(localizeMe); | ||
``` | ||
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If you compile this, you'll get errors: | ||
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* `Cannot use local variable 'adj' before it is declared` - the `adj` variable wasn't declared until *after* the interpolated string. | ||
* `The name 'otheranimal' does not exist in the current context` - a variable called `otheranimal` was never even declared | ||
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## Localization and Internationalization | ||
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An interpolated string supports `IFormattable` and `FormattableString`, which can be useful for internationalization. | ||
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By default, an interpolated string uses the current culture. To use a different culture, you could cast it as `IFormattable` | ||
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For instance: | ||
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[!code-csharp[Interpolation internationalization example](../../../samples/snippets/csharp/new-in-6/string-interpolation.cs#InterpolationInternationalizationExample)] | ||
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## Conclusion | ||
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In this tutorial, you learned how to use string interpolation features of C# 6. It's basically a more concise way of writing simple `String.Format` statements, with some caveats for more advanced uses of it. |
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using System; | ||
using System.Globalization; | ||
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namespace StringInterpolationTutorial | ||
{ | ||
public class Examples | ||
{ | ||
public void StringFormatExample() | ||
{ | ||
// <StringFormatExample> | ||
var firstName = "Matt"; | ||
var lastName = "Groves"; | ||
var str = String.Format("My name is {0} {1}", firstName, lastName); | ||
Console.WriteLine(str); | ||
// </StringFormatExample> | ||
} | ||
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public void InterpolationExample() | ||
{ | ||
// <InterpolationExample> | ||
var firstName = "Matt"; | ||
var lastName = "Groves"; | ||
var str = $"My name is {firstName} {lastName}"; | ||
Console.WriteLine(str); | ||
// </InterpolationExample> | ||
} | ||
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public void InterpolationExpressionExample() | ||
{ | ||
// <InterpolationExpressionExample> | ||
for(var i = 0; i < 5; i++) { | ||
Console.WriteLine($"This is line number {i + 1}"); | ||
} | ||
// </InterpolationExpressionExample> | ||
} | ||
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public void InterpolationFormattingExample() | ||
{ | ||
// <InterpolationFormattingExample> | ||
var rand = new Random(); | ||
for(var i = 998; i < 1005; i++) | ||
{ | ||
var randomDecimal = rand.NextDouble() * 10000; | ||
Console.WriteLine($"{i, -10} {randomDecimal, 6:N2}"); | ||
} | ||
// </InterpolationFormattingExample> | ||
} | ||
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public void InterpolationInternationalizationExample() | ||
{ | ||
// <InterpolationInternationalizationExample> | ||
var birthday = new DateTime(1980, 1, 29); | ||
Console.WriteLine($"My birthday is {birthday}"); | ||
// This outputs "My birthday is 1/29/1980 12:00:00 AM" | ||
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var birthdayFormattable = (IFormattable)$"My birthday is {birthday}"; | ||
Console.WriteLine(birthdayFormattable.ToString(null, new CultureInfo("fr-FR"))); | ||
// This outputs "My birthday is 29/01/1980 00:00:00" | ||
// </InterpolationInternationalizationExample> | ||
} | ||
} | ||
} |
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Let's add a link to the format strings doc https://msdn.microsoft.com/en-us/library/dwhawy9k(v=vs.110).aspx here to explain how that works.
(We'll catch and update those links when that section in MSDN is migrated).