最后块是如何工作的。 [英] How finally block works.

问题描述

我必须知道finally块实际执行的时间。在异常发生后最终阻止执行还是会正常执行？

代码片段：

 尝试 
 {
 如果（txt_password.Text == txt_cpassword.Text）
 {
 con.Open（）; 
 cmd =  new  SqlCommand（  DELETE FROM LoginTB WHERE Username =' + txt_username.Text +  'AND Password =' + txt_cpassword.Text +  '，con）; 
 cmd.ExecuteNonQuery（）; 
 MessageBox.Show（ 用户帐户已删除）; 
} 
  else  
 {
 MessageBox.Show（ 抱歉...密码与确认密码）不匹配; 
} 
} 
  catch （例外）
 {
 MessageBox.Show（ 无效的操作）; 
} 
 最后 
 {
 con.Close（）; 
} 

如果尝试 - catch块没有给我任何异常意味着它通常执行到它想要的结果。

if我在finally块中写con.Close（）是否有连接关闭或者我必须在try块中写con.Close（）。



感谢你。

解决方案

简单来说，无论异常如何， finally 都可以保证执行。请参阅： try-catch-finally（C＃参考） [ ^ ]



它声明：

Quote：

catch的常见用法，最后一起是获取和使用try块中的资源，处理catch块中的异常情况，并释放finally块中的资源。

旁注：



使用参数化查询总是好的。也就是说，

 DELETE FROM LoginTB WHERE Username = ' + txt_username.Text +'  AND Password = ' + txt_cpassword.Text +' 

应该进行修改以防止SQL注入攻击。



请参阅：使用参数化查询来防止sql server中的sql注入攻击 [ ^ ]

finally 块总是执行 - 无论是否有错误。

规则拇指是尽可能晚地打开。尽快关闭。使用using语句将确保。



看看 http://msdn.microsoft.com/en-us/library/vstudio/yh598w02.aspx。



出于这个原因，我通常会这样做：



使用（MySqlConnection con = new MySqlConnetion（connectionString）

{

con.open（）;

//在这里执行数据库查询



} // con关闭并在退出时立即处理< br $> b $ b



这里有一个很好的例子：

http://www.dotnetperls.com/sqlconnection

I have to know when finally block actually executed.finally block executed after the exception occurred or will executed normally?
code snippet:

try
{
   if (txt_password.Text == txt_cpassword.Text)
   {
     con.Open();
     cmd = new SqlCommand("DELETE FROM LoginTB WHERE Username = '" + txt_username.Text + "' AND Password = '" + txt_cpassword.Text + "'", con);
     cmd.ExecuteNonQuery();
     MessageBox.Show("User account Deleted");
   }
    else
      {
       MessageBox.Show("Sorry...Password does not match with confirm password ");
      }
}
catch (Exception)
  {
   MessageBox.Show("Invalid operation");
  }
finally
  {
   con.Close();
  }

If try - catch block don't give me any exception means it normally executed to its desired result.
if I write con.Close() in finally block is there connection close or I have to write con.Close() in try block.

Thanking you.

解决方案

In very simple terms,finally is guaranteed to execute regardless of exception. See this : try-catch-finally (C# Reference)[^]

It states that:

Quote:

A common usage of catch and finally together is to obtain and use resources in a try block, deal with exceptional circumstances in a catch block, and release the resources in the finally block.

Side note:

It is always good to use parameterized query. That is,

DELETE FROM LoginTB WHERE Username = '" + txt_username.Text + "' AND Password = '" + txt_cpassword.Text + "'

should be modified to prevent SQL injection attacks.

See this : Using parameterized queries to prevent sql injection attacks in sql server[^]

The finally block always executes - irrespective of whether there is an error or not.

The rule of thumb is "open as late as possible. Close asap". Use "using" statement will ensure that.

Take a look at http://msdn.microsoft.com/en-us/library/vstudio/yh598w02.aspx.

For this reason, I usually do this:

using(MySqlConnection con= new MySqlConnetion(connectionString)
{
con.open();
// perform database query here

} //con gets closed and disposed immediately upon exits


There is a good example here:
http://www.dotnetperls.com/sqlconnection

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