List,
I just wanted to point out another solution from Bill Thoen that seems
to be pretty bulletproof:
function IsNumeric (byval sVal as string) as logical
dim i as integer
For i = 1 to Len(sVal)
If NOT InStr (1, " 0123456789.+-e", mid$(sVal,i,1)) Then
'String contains a non-numeric character!
Exit Function
End If
Next
IsNumeric = 1
end function
It basically steps through the string that's being evaluated, testing
each character against a list of 'legal' numeric characters, and if it
finds one that's 'illegal', exits the function and returns FALSE.
Intuitively you would expect that this approach would be much slower,
but in practical usage it blazes along just as fast as the str$(val())
method.
Tim Nuteson
Target
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Sent: Tuesday, May 18, 2004 9:43 AM
To: Spencer Simpson
Cc: [EMAIL PROTECTED]
Subject: RE: MI-L Testing to ensure a string is numeric
Spencer,
In terms of speed, I would mostly stick with just the val function. Just
the idea that converting a string to a number and back to a string and
comparing them is fraught with danger, at least for floating point.
Note that the val function returns a number. It returns 0 for things
that don't parse and for real zeroes. So if you had code like:
num = val(somestring)
if num <> 0 then ' this is definitely a number
' return true
else
' parse the string looking for spaces/tabs and then a 0 digit to
determine a true 0 endif
This code will be much faster if you think that you usually do have
numbers. The val function will do all the work for you. Call it an
optimistic implementation. You can even design the function so it
returns the number on success so that you don't bother doing it again.
Eric Blasenheim
Software Architect
MapInfo Corporation
Mail List:
[EMAIL PROTECTED]
From: on 05/17/2004 11:54 AM AST
To: <[EMAIL PROTECTED]>
cc:
Subject: RE: MI-L Testing to ensure a string is numeric
No, it will notThere are a couple of ways to implement them, some of
which are more efficient than others.
The str$(val()) method is the fastest method, but it's not the most
robust. For one thing, it works only for integers. However, it's great
for quick applications that require only integers.
For robust, idiot-proof applications, you need more sophisticated
validation routines.
It is possible, of course, to write a routine that scans the string for
the correct format, but this can be very slow, given that you have to
make calls to mid$() for every character in the string. If you've been
programming for any length of time, you've probably written one that you
can adapt to MapBasic. Or you can write one in a faster language, put
it in a DLL, and link to it from MapBasic (scanf is NOT recommended).
Another method is to try assigning the string to a MapBasic window
variable, and catching any errors. This method is optimal for validating
strings that can take non-integer values.
run command "Dim v_dbl as float"
...
function good_float (ByVal s as string, f as float) as logical On Error
Goto notvalid run command "v_dbl="+sval OnError goto 0
f=val(Sval)
good_float = true
exit function
notvalid: resume failure
failure: good_float = false
end function
Hope this helps
Spencer
-----Original Message-----
From: B. Thoen [mailto:[EMAIL PROTECTED]
Sent: Monday, May 17, 2004 11:05 AM
To: Tim.Nuteson
Cc: [EMAIL PROTECTED]
Subject: Re: SUM: MI-L Testing to ensure a string is numeric
Would that algorithm return the correct result if you fed it a numeric
string like '0023456', or are numbers with leading zeros not going to be
encountered?
On Mon, 17 May 2004, Tim.Nuteson wrote:
> Thanks to all who responded to my question: How can I ensure that a
> value entered into an EditText control of a MB dialog is numeric? The
> simplest solution was offered by Michael Taylor, Martin Highham, and
> Robert Crossley:
>
> If str$(val(teststring)) = teststring then
> 'numeric
> Else
> 'not
> End If
>
> Thanks again,
>
> Tim Nuteson
> Target
>
>
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