On Error
Error handling statement to set the current error handler
Syntax
`
On [Local] Error Goto label
`
Parameters
`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.
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:
Print "Error #"; Err; "!"
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
`
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`
- `Runtime Error Codes`
- `Error Handling`
- `Labels`