CType vs. Parse

I started to say...
"Well, it depends upon how much you trust the data, and what you're willing to sacrifice in performance for better checking."
Then I thought I would do some performance checking so that I'd have actual data. Turned out the empirical evidence didn't agree with my initial thoughts.
Take the following example:

Imports System Imports System.Globalization Imports Microsoft.VisualBasic Module DecimalParseDemo Public Enum CastType Parse [CType] [DirectCast] End Enum Public Function DecimalParse(ByVal castType As CastType) As Integer Dim errorCount As Integer = 0 Dim decimalFormats As String() = { _ "9876543210.9876543210", "9876543210,9876543210", _ "(9876543210,9876543210)", _ "9,876,543,210,987,654.3210", _ "9.876.543.210.987.654,3210", _ "98_7654_3210_9876,543210"} Dim decimalString As Object For Each decimalString In decimalFormats Dim decimalNumber As Decimal Try Select Case castType Case DecimalParseDemo.CastType.Parse decimalNumber = Decimal.Parse(decimalString) Case DecimalParseDemo.CastType.CType decimalNumber = CType(decimalString, Decimal) Case DecimalParseDemo.CastType.DirectCast decimalNumber = DirectCast(decimalString, Decimal) End Select Catch ex As Exception errorCount = errorCount + 1 End Try Next decimalString Return errorCount End Function Sub Main() Dim finish As Date Dim start As Date Dim errorCount As Integer errorCount = 0 start = Date.Now For i As Integer = 1 To 1000 errorCount = errorCount + DecimalParse(CastType.Parse) Next finish = Date.Now Console.WriteLine("Time to do 6000 Decimal.Parses = " & finish.Subtract(start).ToString()) Console.WriteLine("Decimal.Parse reported " & errorCount & " error(s).") errorCount = 0 start = Date.Now For i As Integer = 1 To 1000 errorCount = errorCount + DecimalParse(CastType.CType) Next finish = Date.Now Console.WriteLine("Time to do 6000 CTypes = " & finish.Subtract(start).ToString()) Console.WriteLine("CType reported " & errorCount & " error(s).") errorCount = 0 start = Date.Now For i As Integer = 1 To 1000 errorCount = errorCount + DecimalParse(CastType.DirectCast) Next finish = Date.Now Console.WriteLine("Time to do 6000 DirectCasts = " & finish.Subtract(start).ToString()) Console.WriteLine("DirectCast reported " & errorCount & " error(s).") End Sub End Module

My output was:
Time to do 6000 Decimal.Parses = 00:00:07.4807568
Decimal.Parse reported 3000 error(s).
Time to do 6000 CTypes = 00:00:13.0988352
CType reported 2000 error(s).
Time to do 6000 DirectCasts = 00:00:14.1603616
DirectCast reported 6000 error(s).
This output was very surprising to me. Initially I expected DirectCast to be the fastest, but apparently since Decimal doesn't inherit from String, it just throws an exception and can't parse any of the items. Exception handling is always slow, so that bumps it up to the slowest, so that made sense to me once I thought about it.
However, the differences between Parse and CType are still somewhat surprising. Parse reported more errors, which I expected, but it was also faster, in spite of reporting more errors, which I didn't expect at all. So, given this data sample, Parse seems to be the way to go, but in the lnog run, it may depend upon your data.
I ran this test several times. Sometimes DirectCast was the slowest, and sometimes CType. Decimal.Parse was always the fastest.

Heh!

But do you regret asking it? I don't regret reading it.

Faster still is Decimal.TryParse, as you don't use the catch block.

if decimal.tryparse(decimalString, decimalNumber) = false then
errorcount += 1
end if

Time to do 600000 Decimal.Parses = 00:00:25.5467344
Decimal.Parse reported 300000 error(s).
Time to do 600000 CTypes = 00:00:48.9203440
CType reported 200000 error(s).
Time to do 600000 DirectCasts = 00:00:49.6113376
DirectCast reported 600000 error(s).
Time to do 600000 DecimalTryParses = 00:00:00.4606624
DecimalTryParse reported 300000 error(s).
Press any key to continue . . .

The catch block is VERY demanding!! Mind you, for validating textboxes you are not going to notice the performance difference (unless the users are cylons).