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Exception Trapping (Cross Ref > Statements)

Exception Trapping

Languages Focus

A common usage of exception handling is to obtain and use resources in a "try-it" block, deal with any exceptions in an "exceptions" block, and release the resources in some kind of "final" block which executes whether or not any exceptions are trapped.

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

Using On Error Resume Next

C#: try...catch...finally

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

try {}

catch {}

finally {}

Syntax Example:

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

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

C++: try/catch

Syntax Example:

try {

  //Some code.

catch(AnError) {

  //Error code here.

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

Debugging ObjectPAL Code

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;

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;

Java: try/catch/finally

Syntax Example:

try {

  /* Risky code here. */

catch (SomeException) {        //one or more.

  /* Recovery here. */

finally {                      //0 or one.

  /* Do something. */

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.

VB.Net: Try...Catch...Finally

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

Try
Catch
Finally
End Try

Syntax Example:

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) 1 certification question.