# Compiler Error CS0103 當前上下文中不存在名稱“identifier” 嘗試使用類、[命名空間](https://msdn.microsoft.com/zh-cn/library/z2kcy19k.aspx)或范圍中不存在的名稱。檢查名稱的拼寫，并檢查 正在使用的目錄和程序集引用，確保您嘗試使用的名稱可用。 如果在循環或者 **try** 或 **if** 塊中聲明一個變量，然后嘗試從封閉代碼塊或一獨立代碼塊訪問此變量，經常會發生此錯誤。如下面的示例所示。 ``` using System; class MyClass1 { public static void Main() { try { // The following declaration is only available inside the try block. MyClass1 conn = new MyClass1(); } catch (Exception e) { // The following expression causes error CS0103, because variable // conn only exists in the try block. if (conn != null) Console.WriteLine("{0}", e); } } } ``` 下面的示例解決錯誤。 ``` using System; class MyClass2 { public static void Main() { // To resolve the error in the example, the first step is to // move the declaration of conn out of the try block. The following // declaration is available throughout the Main method. MyClass2 conn = null; try { // Inside the try block, use the conn variable that you declared // previously. conn = new MyClass2(); } catch (Exception e) { // The following expression no longer causes an error, because // the declaration of conn is in scope. if (conn != null) Console.WriteLine("{0}", e); } } } ```