Exception Trapping (Cross Ref > Statements)

Exception Trapping

ASP Classic:   On Error

Syntax Example: On Error Resume Next Response.Write FormatDateTime(f_CurrentActualDate, vbShortDate) If ErrNumber <> 0 Then Break(f_CurrentActualDate) End If On Error Goto 0 More Info  To/From Code Guide: Exception Trapping (Cross Ref > Statements) vs. Other Languages KB Post:  Using On Error Resume Next

 Using On Error Resume Next

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 To/From Code Guide: Exception Trapping (Cross Ref > Statements) vs. Other Languages

C#:   try...catch...finally

C# uses a try...catch...finally statement to trap for errors.

try {}

catch {}

finally {}

try
{
  int y = 0;
  y = 1 / y;
}
catch
{
  MessageBox.Show("you cannot divide by zero");
}

 C# Exception Trapping (try...catch...finally)

Complete Simple Example

Here is a complete example using a button click event:

private void button6_Click(object sender, EventArgs e)
{
  try
  {
    MessageBox.Show("Before Error");
    int y = 0;
    y = 1 / y;
    MessageBox.Show("This line never executes: " + y);
  }
  catch
  {
    MessageBox.Show("you cannot divide by zero");
  }
  finally
  {
    MessageBox.Show("This line always executes.");
  }

}

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C# Exception Trapping (try...catch...finally)

C++:   try/catch

Syntax Example: try { //Some code. } catch(AnError) { //Error code here. } More Info  To/From Code Guide: Exception Trapping (Cross Ref > Statements) vs. Other Languages

Corel Paradox:   try...onFail

ObjectPAL has a try...onFail statement but does not have a finally-type component. However, the code afer endTry will execute.

try

onFail

endTry

Syntax Example: var i SmallInt endVar try i = 0 i = 1/i onFail msgInfo("", "You cannot divide by zero.") endTry Here is an example from a pushButton event: method pushButton(var eventInfo Event) var  i SmallInt endVar errorTrapOnWarnings(True) try   i = 0   i = 1/i   msgInfo("", "This line of code never executes.") onFail   msgInfo("", "You cannot divide by zero.") endTry msgInfo("", "This line always executes.") endMethod The following example shows you the last ObjectPAL error: errorTrapOnWarnings(yes) try ;Your code here onFail msgStop( errorCode(), errorMessage() ) ;You could also use errorShow() endTry More Info  To/From Code Guide: Exception Trapping (Cross Ref > Statements) vs. Other Languages Article:  Debugging ObjectPAL Code

 Debugging ObjectPAL Code

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 To/From Code Guide: Exception Trapping (Cross Ref > Statements) vs. Other Languages

Delphi:   try..except, try..finally

Use a try..except..end block to trap and process errors.

Delphi also offers a try...finally where code will execute in the finally section no matter what. It's common to put a try..except inside a try..finally.

Syntax Example: var y : Double; begin try y := 0; y := (1/y); ShowMessage(FloatToStr(y)); except ShowMessage('You cannot divide by zero.'); end; end; More Info  To/From Code Guide: Exception Trapping (Cross Ref > Statements) vs. Other Languages

Delphi Prism:   try..except, try..finally

Use a try..except..end block to trap and process errors.

Delphi also offers a try...finally where code will execute in the finally section no matter what. It's common to put a try..except inside a try..finally.

Syntax Example: try   var y: Integer;   y := 0;   y := 1/y; except   MessageBox.Show("You cannot divide by zero."); end; More Info  To/From Code Guide: Exception Trapping (Cross Ref > Statements) vs. Other Languages

Java:   try/catch/finally

Syntax Example: try { /* Risky code here. */ } catch (SomeException) { //one or more. /* Recovery here. */ } finally { //0 or one. /* Do something. */ } More Info  To/From Code Guide: Exception Trapping (Cross Ref > Statements) vs. Other Languages

JavaScript:   try/catch/finally

See "throw" to raise (throw) an error.

Syntax Example: try { //Do something. } catch(e) { //one or more. //Do something. } finally { //0 or one. //Do something. } More Info  To/From Code Guide: Exception Trapping (Cross Ref > Statements) vs. Other Languages

VB.Net:   Try...Catch...Finally

VB.Net uses a try...catch...finally statement to trap for errors.

Try
Catch
Finally
End Try

Try
  Dim y As Integer = 0
  y = 1 / y
Catch
  MessageBox.Show("you cannot divide by zero")

End Try

 VB.Net Exception Trapping (Try...Catch...Finally)  

Complete Simple Example

Here is a complete example using a button click event:

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
  Try
    MessageBox.Show("Before Error")
    Dim y As Integer = 0
    y = 1 / y
    MessageBox.Show("This line never executes: " + y)
  Catch
    MessageBox.Show("you cannot divide by zero")
  Finally
    MessageBox.Show("This line always executes.")
  End Try
End Sub

Linked Certification Question(s)

The following are practice certification questions with answers highlighted. These questions were prepared by Mike Prestwood and are intended to stress an important aspect of this KB post. All our practice questions are intended to prepare you generally for passing any certification test as well as prepare you for professional work.

Intermediate

1 Intermediate Level Question

Question #1: Multiple Choice Which of the following syntax templates is used for error handling?

Answer: 1.  Try Except Final End Try 2.  Try OnFail OnFinal End Try 3.  Try Handle Exception Do Final End Try 4.  Try Catch Finally End Try 5.  Try Exception Cleanup End Try

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Code:

VB.Net Exception Trapping (Try...Catch...Finally)