C#中字符串前面的@是什么？

发布于 2024-07-14 11:48:14 字数 202 浏览 9 评论 0原文

这是 C#（或者可能是 VB.net）的 .NET 问题，但我试图弄清楚以下声明之间有什么区别：

string hello = "hello";

与

string hello_alias = @"hello";

在控制台上打印没有区别，长度属性是相同的。

原文

This is a .NET question for C# (or possibly VB.net), but I am trying to figure out what's the difference between the following declarations:

string hello = "hello";

vs.

string hello_alias = @"hello";

Printing out on the console makes no difference, the length properties are the same.

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迷荒 2024-07-21 11:48:14

它将字符串标记为逐字字符串文字 - 字符串中通常会被解释的任何内容因为转义序列被忽略。

因此 "C:\\Users\\Rich" 与 @"C:\Users\Rich" 相同，但

有一个例外：需要转义序列双引号。要转义双引号，您需要将两个双引号放在一行中。例如，@"""" 的计算结果为 "。

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花开浅夏 2024-07-21 11:48:14

这是一个逐字字符串。这意味着不应用转义。例如：

string verbatim = @"foo\bar";
string regular = "foo\\bar";

这里的verbatim和regular有相同的内容。

它还允许多行内容 - 这对于 SQL 来说非常方便：

string select = @"
SELECT Foo
FROM Bar
WHERE Name='Baz'";

逐字字符串文字所需的一点转义是通过将其加倍来获得双引号 (")：

string verbatim = @"He said, ""Would you like some coffee?"" and left.";
string regular = "He said, \"Would you like some coffee?\" and left.";

It's a verbatim string literal. It means that escaping isn't applied. For instance:

string verbatim = @"foo\bar";
string regular = "foo\\bar";

Here verbatim and regular have the same contents.

It also allows multi-line contents - which can be very handy for SQL:

string select = @"
SELECT Foo
FROM Bar
WHERE Name='Baz'";

The one bit of escaping which is necessary for verbatim string literals is to get a double quote (") which you do by doubling it:

string verbatim = @"He said, ""Would you like some coffee?"" and left.";
string regular = "He said, \"Would you like some coffee?\" and left.";

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分開簡單 2024-07-21 11:48:14

“@”还有另一个含义：将其放在变量声明前面允许您使用保留关键字作为变量名。

例如：

string @class = "something";
int @object = 1;

我只发现了一两个合法用途。主要在 ASP.NET MVC 中，当您想做这样的事情时：

<%= Html.ActionLink("Text", "Action", "Controller", null, new { @class = "some_css_class" })%>

这会产生一个 HTML 链接，例如：

<a href="/Controller/Action" class="some_css_class">Text</a>

否则，您将不得不使用“Class”，它不是保留关键字，但大写的“C”不遵循 HTML标准，但看起来不正确。

An '@' has another meaning as well: putting it in front of a variable declaration allows you to use reserved keywords as variable names.

For example:

string @class = "something";
int @object = 1;

I've only found one or two legitimate uses for this. Mainly in ASP.NET MVC when you want to do something like this:

<%= Html.ActionLink("Text", "Action", "Controller", null, new { @class = "some_css_class" })%>

Which would produce an HTML link like:

<a href="/Controller/Action" class="some_css_class">Text</a>

Otherwise you would have to use 'Class', which isn't a reserved keyword but the uppercase 'C' does not follow HTML standards and just doesn't look right.

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站稳脚跟 2024-07-21 11:48:14

既然您也明确要求使用 VB，那么让我补充一下，这种逐字字符串语法在 VB 中不存在，仅在 C# 中存在。相反，所有字符串在 VB 中都是逐字的（除了它们不能包含换行符这一事实，这与 C# 逐字字符串不同）：

Dim path = "C:\My\Path"
Dim message = "She said, ""Hello, beautiful world."""

VB 中不存在转义序列（除了双引号字符之外），就像在 C# 逐字字符串中一样），这使得一些事情变得更加复杂。例如，要在 VB 中编写以下代码，您需要使用串联（或任何其他方式来构造字符串）

string x = "Foo\nbar";

在 VB 中，这将编写如下：（

Dim x = "Foo" & Environment.NewLine & "bar"

& 是 VB 字符串可以同样使用连接运算符。）

Since you explicitly asked for VB as well, let me just add that this verbatim string syntax doesn't exist in VB, only in C#. Rather, all strings are verbatim in VB (except for the fact that they cannot contain line breaks, unlike C# verbatim strings):

Dim path = "C:\My\Path"
Dim message = "She said, ""Hello, beautiful world."""

Escape sequences don't exist in VB (except for the doubling of the quote character, like in C# verbatim strings) which makes a few things more complicated. For example, to write the following code in VB you need to use concatenation (or any of the other ways to construct a string)

string x = "Foo\nbar";

In VB this would be written as follows:

Dim x = "Foo" & Environment.NewLine & "bar"

(& is the VB string concatenation operator. + could equally be used.)

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绿阴红影里的.如风往事 2024-07-21 11:48:14

http://msdn.microsoft.com/en-us/library/aa691090.aspx

C# 支持两种形式的字符串文字：常规字符串文字和逐字字符串文字。

常规字符串文字由零个或多个用双引号括起来的字符组成，如“hello”，并且可能包括简单的转义序列（例如制表符的 \t）以及十六进制和 Unicode 转义序列。

逐字字符串文字由 @ 字符后跟双引号字符、零个或多个字符以及结束双引号字符组成。一个简单的例子是@“hello”。在逐字字符串文字中，分隔符之间的字符将逐字解释，唯一的例外是引号转义序列。特别是，简单转义序列以及十六进制和 Unicode 转义序列不会按逐字字符串文字进行处理。逐字字符串文字可以跨越多行。

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┈┾☆殇 2024-07-21 11:48:14

这是一个逐字字符串，并更改转义规则 - 现在转义的唯一字符是“，转义为””。这对于文件路径和正则表达式特别有用：

var path = @"c:\some\location";
var tsql = @"SELECT *
            FROM FOO
            WHERE Bar = 1";
var escaped = @"a "" b";

等

This is a verbatim string, and changes the escaping rules - the only character that is now escaped is ", escaped to "". This is especially useful for file paths and regex:

var path = @"c:\some\location";
var tsql = @"SELECT *
            FROM FOO
            WHERE Bar = 1";
var escaped = @"a "" b";

etc

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丘比特射中我 2024-07-21 11:48:14

复制自 MSDN：

在编译时，逐字字符串将转换为具有所有相同转义序列的普通字符串。因此，如果您在调试器监视窗口中查看逐字字符串，您将看到编译器添加的转义字符，而不是源代码中的逐字版本。例如，逐字字符串 @"C:\files.txt" 将在监视窗口中显示为 "C:\\files.txt"。

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蓝天白云 2024-07-21 11:48:14

将 @ 放在字符串前面使您可以使用特殊字符，例如反斜杠或双引号，而不必使用特殊代码或转义字符。

所以你可以写：

string path = @"C:\My path\";

而不是：

string path = "C:\\My path\\";

Putting a @ in front of a string enables you to use special characters such as a backslash or double-quotes without having to use special codes or escape characters.

So you can write: