error trapping ?

[pnj]

Hey,
can someone give me the simplest example of error trapping?
if there is no simple example, no prob.
thanks

[Mongo]

Function uh() As Boolean
Dim i as Integer
  On Error Goto Oops
  i = 'a'
  uh = true
  exit function
Oops:
  uh = false
End Function

This example will create an Overflow and display a
MessageBox telling us what happened.

'The VB to go to ERR_HANDLE if an Error occurs
On Error GoTo ERR_HANDLE
    'Create an Overflow (Error 6)
    Err.Raise 6
Exit Sub

ERR_HANDLE:
'Display a MessageBox telling us we have an Error
If Err = 6 Then MsgBox ("Over flow, click to resume")

[pnj]

I am sure there is a good reason to do this but I am not yet sure why. When my programs have problems they automaticly tell me.
but mine are not .exe so maybe that is why.
um...don't know.
I am geussing this is a way to track errors in a program.
so would you say something like
if err=6 then
if err=4 then
if err=3 then....ect.
and list every error possible?
I am new to this can you tell?
thanks

If you want to some a specific action when a specific error occurs, yes, you can use the above statements. Use the On Error Resume Next statement to skip the statement where the error occured and continue execution of the program.

'If an Error occurs, skip that statement
'continue execution of the program
On Error Resume Next
'Create an Overflow (Error 6)
Err.Raise 6
Print "Hello"

[rammy]

you can also use "Err.Description" to display the error message.

code:

On Error GoTo ErrMsg
'your code

ErrMsg:
Msgbox Err.Description

[Crazy D]

pnj:
If you run a program from within VB it depends on the settings when and how an error is shown.
But in exe's, it doesn't work that way....

The other examples show how to trap an error.
If you know you can expect certain errors (for instance, file does not exist, file is locked, etc), you can add to you errorhandler:
If Err.Number = <certain number> Then
' action here
ElseIf Err.Number = <other number> Then
' do something else
Else
' display an error, shutdown windows, whatever
End If

That way you can do specific task when certain errors occur.

[kedaman]

Error trapping is the weak programmers easy way out.

Ok, that was maybe not what i meant but i thought it sounded very familiar in some way. Well but that's somehow became my motto

Often you can avoid error handling by just using if statement to prevent the error from occuring,
I.E:

If a<>0 then c=b/a

but sometimes you have to deal with it, whenever you don't know how to prevent it:

On error resume next
c=b/a
if err=11 then err.clear:msgbox "Division by 0"

[Sam Finch]

I'd Dissagree with that ked.

I use error trapping if I'm using the same function in a huge loop where in some cases the parameters will raise an error. For example if I'm making an ActiveX control that paints itself to look like a shere, the way I do this is to go through every pixel in my grid, find out it's distance from the centre and then find the colour of that picel based on

Sqr((usercontrol.Width * usercontrol.Width * 4) - (R * R))

This will raise an error if its radius is greater than usercontrol.width/2 it's quicker to set up an error trap and just skip some code if this raises an error than it would be to check it myself, especially if it's a large activeX control with lots of pixels to calculate.