c# using 不带分号的语句

Question

我在网上找到了以下代码：

using (SqlConnection con = new SqlConnection(connectionString))
    {
        //
        // Open the SqlConnection.
        //
        con.Open();
        //
        // The following code uses an SqlCommand based on the SqlConnection.
        //
        using (SqlCommand command = new SqlCommand("SELECT TOP 2 * FROM Dogs1", con))
        using (SqlDataReader reader = command.ExecuteReader())
        {
        while (reader.Read())
        {
            Console.WriteLine("{0} {1} {2}",
            reader.GetInt32(0), reader.GetString(1), reader.GetString(2));
        }
        }
    }

任何人都可以向我解释为什么使用 (SqlCommand ..) 不以分号结尾。我的第二个问题通常是在使用之后我们必须有 {} 来指示使用变量的范围为什么在这种情况下它丢失了？以及如何，何时处理命令对象？

Answer 1

using 结构不要求语句以分号结尾。

using 结构会自动确保正确处理您的对象。

如果 {} 不存在，则范围是下一个语句。在您的情况下，这是整个 using(SqlReader...) 块，因为它的范围是 {}

Answer 2

can anyone explain me why using (SqlCommand ..) doesn't end with semicolon

因为 using 命令将运行恰好是一个块：下一个块。该块只能是一个语句。如果你在末尾放一个分号，它什么都不做（运行一个空语句）。

这与 'if' 的情况相同。

if(a==b)
   Console.Write("they are equal!");

Console.Write("I'm outside the if now because if only runes one block");

但是

if(1==2);
Console.Write("I will always run because the if ends with a semicolon! (executes an empty statement)");

my second question is generally after using we have to have { } to indicate scope of that using variable why in this case it is missing?

不是，仔细看

and how, when will it dispose command object?

它会在块结束时调用 object.Dispose()（如果它不为空）（即使它抛出异常）。

Answer 3

can anyone explain me why using (SqlCommand ..) doesn't end with semicolon.

Using、If、For 和 Foreach 等关键字不需要 ;标记结束因为还没有结束！您永远不会发现这样有用的代码。

If(true);//This is totally meaningless code
Console.WrtieLine("Hello world!");

my second question is generally after using we have to have { } to indicate scope of that using variable why in this case it is missing?

因为在这种情况下可以安全地确定外部 using 块的范围。

using (SqlCommand command = new SqlCommand("SELECT TOP 2 * FROM Dogs1", con))
using (SqlDataReader reader = command.ExecuteReader())

同样你也可以这样写

for (int i = 0; i < 3; i++)
    for (int j = 0; j < 2; j++)
    {
        Console.WriteLine(string.Format("i = {0}, j ={1}",i, j));
    }
//i and j are no longer accessible from this line after
//because their scopes ends with the }

and how, when will it dispose command object?

很好地解释了使用语句的整个概念here

c# using 不带分号的语句

c# using statements without semicolon

c#

ado.net

using