On Error

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On Error

Sets a label to jump to when a runtime error happens; On Error Goto 0 turns it off.

Syntax

On [Local] Error Goto label

Parameters

• label

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.

See also

• Error
• Local
• Err
• Error Handling

Examples

on error goto errorhandler

error 24 '' simulate an error

print "this message will not be seen"

errorhandler:

dim as int32 n = err

print "Error #"; n; "!"

end

'' compile with: tiko onerror.tiko -ex

function hFileExists( byref filename as string ) as boolean

    dim as long f = freefile

    on local error goto exitfunction

    open filename for input as #f

    close #f

    return true

exitfunction:

    return false

end function

print "File exists: "; hFileExists( command( 1 ) )

on error goto errhandler

error 1234

print "not seen: an error handler cannot return here"

end 0

errhandler:

print "error number: " + str( err ) + " at line: " + str( erl )

end 1

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Category: Error Handling Functions
Kind: keyword

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Reproduced from the FreeBASIC Wiki Manual under the GNU Free Documentation License 1.3 — with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. Copyright © the FreeBASIC project and wiki contributors. See License.