CATCH

Marks the beginning of a code block to be executed if an exception happens in the main portion of a subroutine

Implemented by: Gambas

With variations:

Also written as:

Usage

CATCH is used in the body of a subroutine, right before its END, for defining a portion of code that must be executed if an exception/error occurs somewhere in the subroutine out of a TRY block.

It is important to notice that a CATCH block in Gambas must be placed after an occasional FINALLY block in the subroutine. The following example is found in Gambas documentation: 

SUB PrintFile(FileName AS STRING)
 
  DIM hFile AS File
  DIM sLig AS STRING
 
  hFile = OPEN FileName FOR READ
 
  WHILE NOT EOF(hFile)
    LINE INPUT #hFile, sLig
    PRINT sLig
  WEND
 
FINALLY ' Always executed, even if a error is raised. Warning: FINALLY must come before CATCH!
  CLOSE #hFile
 
CATCH ' Executed only if there is an error
  PRINT "Cannot print file "; FileName
 
END

Comments

At the time of this writing, CATCH seemed to be an oddity of Gambas only — alas, in most BASICs error handling is not exactly an area of excellence.

The fact that a FINALLY block must precede a CATCH block is counter-intuitive, and not by fortune different of every other programming language that implements "try-catch-finally" error handling.

Similar keywords

In other languages...

Most languages that have a catch statement use it as part of a try block. Quite often, multiple catch blocks can be used for treating different types of errors or exceptions. Java and PHP are some examples.

Tcl had a catch command long before it had try blocks, but it works somehow like a traditional try.

References

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