c#“using”语句后跟try语句可以在这种情况下对括号进行ombitted

发布时间：2020-12-15 04:17:22 所属栏目：百科来源：网络整理

导读：using System.Net; // (See Chapter 16) ... string s = null; using (WebClient wc = new WebClient()) // why there is no brackets after this using statement try { s = wc.DownloadString ("http://www.albahari.com/nutshell/"); } catch (WebExcepti

using System.Net;       // (See Chapter 16)
   ...
  string s = null;
  using (WebClient wc = new WebClient()) // why there is no brackets after this using statement
      try { s = wc.DownloadString ("http://www.albahari.com/nutshell/");  }
      catch (WebException ex)
      {
        if (ex.Status == WebExceptionStatus.Timeout)

          Console.WriteLine ("Timeout");
        else
          throw;     // Can't handle other sorts of WebException,so rethrow
      }

上面的代码是cuts在一个Nutshell中的副本,我不明白为什么在using语句后缺少{},这是书中的拼写错误(不太可能)还是不需要？因为语法是使用需要跟随{}内的代码块.

我希望这段代码是：

using System.Net;       // (See Chapter 16)
   ...
  string s = null;
  using (WebClient wc = new WebClient()) // why there is no brackets after this using statement
  {
      try { s = wc.DownloadString ("http://www.albahari.com/nutshell/");  }
      catch (WebException ex)
      {
        if (ex.Status == WebExceptionStatus.Timeout)

          Console.WriteLine ("Timeout");
        else
          throw;     // Can't handle other sorts of WebException,so rethrow
      }
  }

解决方法

如果你看一下 C# Specification中using语句的语法,你会看到using语句后跟(或者更确切地说,它们的主体由“embedded_statements”组成).

using_statement
    : 'using' '(' resource_acquisition ')' embedded_statement
    ;

嵌入式语句定义如下：

embedded_statement
    : block
    | empty_statement
    | expression_statement
    | selection_statement
    | iteration_statement
    | jump_statement
    | try_statement
    | checked_statement
    | unchecked_statement
    | lock_statement
    | using_statement
    | yield_statement
    | embedded_statement_unsafe
    ;

所以是的,这不是一个错字.使用(…)之后,可以在embedded_statement中定义任何语句.无论如何,要想看这是否是一个错字,你可能只是简单地尝试编译示例代码.

（编辑：李大同）

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