On Errorkeyword

Error handling statement to set the current error handler

Error Handling Functionskeyworddocumented

Syntax

On [Local] Error Goto label

Parameters

Name		Description
`label`		Label to jump to when an error occurs

Description

On Error triggers a jump to an error handler when an error occurs. Such errors can be triggered by built-in statements such as Open, or when the Error statement is used.

Note: The error checking for built-in statements is only enabled if the program is compiled with one of the -e, -ex or -exx options. On Error remains working with Error even when none of these options are used.

On Local Error can be used to specify a local error handler inside a procedure. This allows for specialized per-procedure error handling and will override the global error handler, if any.
Without Local, the handler must be in the main part of the module.
Remark: Presently, the Local clause is ignored by the compiler.

On Error Goto 0 deactivates the current error handler.

Remarks

Differences from QB

QB has no LOCAL clause and requires the label to be in the main part of the module.

Example

'' Compile with QB (-lang qb) dialect



'$lang: "qb"



On Error Goto errorhandler

Error 24 '' simulate an error

Print "this message will not be seen"



errorhandler:

n = Err

Print "Error #"; n; "!"

End

'' compile as: fbc onerror.bas -ex



#lang "fblite"



Function hFileExists( filename As String ) As Integer Static

    Dim f As Integer



    hFileExists = 0



    On Local Error Goto exitfunction



    f = FreeFile

    Open filename For Input As #f

    

    Close #f



    hFileExists = -1



exitfunction:

    Exit Function

End Function





    Print "File exists (0=false): "; hFileExists( Command )



    On Error Goto errhandler

    Error 1234

    Print "back from resume next"

    End 0



errhandler:

    Print "error number: " + Str( Err ) + " at line: " + Str( Erl )

    Resume Next

Reference

Documented in KeyPgOnerror.html