CATCH

Estimated reading time: 2 minutes

You can use the TRY…CATCH…FINALLY statements for structured exception handling. This allows you to execute a particular block of statements if a specified exception occurs while your code is running. When this happens, the code is said to throw the exception, and you catch it with the appropriate CATCH command.

CATCH 
Name (Variable name)
Type  (Class filter type)

Parameters

Name

Optional. Any variable name that is used to refer to the trapped exception object. The initial value is the value of the thrown error. If only NAME is given then it must exist in the scope and have an exception type.

Type

Optional. Specifies the type of class filter. If the value of Name is of the type specified by Type or of a derived type, the identifier becomes bound to the exception object.

Remarks

The Try statements are executed first. If no exception occurs, execution continues after the **ENDTRY** (*).

If an exception occurs, then the systems tries to match the exception to the exception types in the CATCH commands. The first one that matches causes the exception to be “trapped” and the catch statements in the matched CATCH to be executed. If the exception is trapped by a CATCH, then after the catch statements are executed, control goes to the next statement after the ENDTRY (*).

If a FINALLY command is present, then the finally statements will always be executed at the end of the TRY / CATCH sequence or TRY /untrapped exception, no matter what.

Rules:

• The only branching commands allowed inside a TRY/CATCH block are LEAVE, ITERATE, and LEAVESR. Any other branching command (CAB, GOTO, etc.) is not allowed in this context. It is also illegal to branch out of a FINALLY clause (i.e., you cannot use any of the branching commands (ITERATE, CAB, LEAVESR, GOTO, etc) in the body of a FINALLY clause.
• The exception Type MUST derive from System.Exception (the mother of all exceptions). A CATCH with a System.Exception type will trap all exceptions.
• If no keywords are specified, then CATCH will trap all exceptions; that is, it will behave as if TYPE( System.Exception ) is given.
• If you have several CATCH commands, the Name must be different at this time.

Example

BEGSR TryCatch access( *Public )
    Dclfld myFld  Type( System.Windows.Forms.Button )
    Dclfld myInt *integer 4
    TRY
       myFld.Show()
       myInt = myInt / 0
 **CATCH**  name( z ) type( System.DivideByZeroException )
       msgbox msg( "by 0" ) Title( z.Message )
 **CATCH**  name( e ) type( System.Exception )
       msgbox msg( "You can't do that!!!" ) Title( e.Message )
    FINALLY
       msgbox "Wow, this works..." 
    ENDTRY
       msgbox "All is well!"
   ENDSR

See Also

FINALLY

THROW

TRY

TRY…CATCH…FINALLY