Difference: throw or throw ex?
Just for demonstrating, if you have classes in C# as follows:
using System;
namespace WindowsApplication2
{
public class Class1
{
public static void DoSomething()
{
try
{
Class2.DoSomething();
}
catch(Exception ex)
{
throw ex;
}
}
}
public class Class2
{
public static void DoSomething()
{
try
{
Class3.DoSomething();
}
catch(Exception ex)
{
throw ex;
}
}
}
public class Class3
{
public static void DoSomething()
{
try
{
int divider=0;
int number=5/divider;
}
catch(Exception ex)
{
throw ex;
}
}
}
}
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And you call:
Class1.DoSomething();
What's the difference if you rethrow the exception using plain 'throw;' or 'throw ex;'?
ANSWER:
If you use "throw ex;", The stack trace is something like:
System.DivideByZeroException: Attempted to divide by zero.
at WindowsApplication2.Class1.DoSomething() in l:\vs.net-projektit\windowsapplication2\main.cs:line 15
at WindowsApplication2.Form1.button1_Click(Object sender, EventArgs e) in l:\vs.net-projektit\windowsapplication2\form1.cs:line 103
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But if you use just 'throw' instead of 'throw ex' to rethrow the same exception, that is: public class Class3
{
public static void DoSomething()
{
try
{
int divider=0;
int number=5/divider;
}
catch
{
throw ;
}
}
}
And of course for all rethrow statements, the stack trace is now like:
System.DivideByZeroException: Attempted to divide by zero.
at WindowsApplication2.Class3.DoSomething() in l:\vs.net-projektit\windowsapplication2\main.cs:line 46
at WindowsApplication2.Class2.DoSomething() in l:\vs.net-projektit\windowsapplication2\main.cs:line 30
at WindowsApplication2.Class1.DoSomething() in l:\vs.net-projektit\windowsapplication2\main.cs:line 15
at WindowsApplication2.Form1.button1_Click(Object sender, EventArgs e) in l:\vs.net-projektit\windowsapplication2\form1.cs:line 103
See the difference? BTW: This concerns both C# and VB. VB docs state that in "Throw expression" the expression would be required. This is not completely true, you can use just "Throw" in VB to rethrow the same exception. C# docs do tell that in "throw expression" the expression "is omitted when rethrowing the current exception object in a catch clause". |