Len vs Empty, which is faster

In Is That String Really Empty? I mentioned that Empty returns the same response as Len when checking variable- and fixed-length strings. Let's test which one is faster.

I am going to assume that Len is faster. To make things simpler I limited my tests to variable-length strings only.

The Test Procedure

As in previous posts, I wrote a simple non-scientific loop to casually test the speed of both functions.

Sub TestLenEmpty()

  Dim i As Long
  Dim str1 As String
  Dim starttimeLen As Single
  Dim endtimeLen As Single
  Dim starttimeEmpty As Single
  Dim endtimeEmpty As Single
  Dim msg As String
  Dim hasValue As Boolean

  Const numberOfLoops As Long = 100000000

  str1 = "Hello World"

  ' use Len
  starttimeLen = Timer
  For i = 1 To numberOfLoops
    hasValue = (Len(str1) > 0)
  Next i
  endtimeLen = Timer

  ' use Empty
  starttimeEmpty = Timer
  For i = 1 To numberOfLoops
    hasValue = (str1 = Empty)
  Next i
  endtimeEmpty = Timer

  msg = "Number of iterations: " & numberOfLoops & vbCrLf
  msg = msg & "Using Len: " & _
    Format(endtimeLen - starttimeLen, "#.###") & " seconds" & vbCrLf
  msg = msg & "Using Empty: " & _
    Format(endtimeEmpty - starttimeEmpty, "#.###") & " seconds" & vbCrLf

  MsgBox msg
End Sub

According to Excel's Visual Basic Help, Empty is a Variant subtype, so I expect some implicit type conversion here when comparing string values to Empty. What I didn't expect was the dramatic difference in speed.

Results

At 100,000 loop iterations, the difference is minimal:

Len vs Empty

At 1,000,000 iterations, both loops are still very quick, but starting to separate:

Len vs Empty

At 10,000,000 iterations it takes a full second longer for the second loop:

Len vs Empty

Finally, at 100 million iterations, the difference is striking: a full eleven seconds longer!

Len vs Empty

Conclusion

There is simply no substitute for Len (no pun intended). It is the fastest method for checking string length (and therefore, whether strings are empty), and it scales well. I never really used Empty anyway, and I don't plan on starting now.

4 Comment(s) on Len vs Empty, which is faster:

Jon writes:

January 12, 2012 at 10:08 am

I'm getting at 10,000,000 iterations:

Len>: 0.640625
Len: 0.671875
IsEmpty(): 0.296875
LenB>: 0.40625
LenB: 0.46875

Where > means I did a comparison with zero and w/o that means I just let VBA do the comparison. IsEmpty is the function. I think I might switch to IsEmpty, it's even faster than LenB! Amazing.
- Jon writes:
  
  January 12, 2012 at 2:33 pm
  
  I take that back. IsEmpty gives the wrong answer if you start using the string, I guess I would need to set my strings to Empty everytime if I wanted to use it. Hmm, I wonder if setting a string to Empty (is that even possible?) compared to "" is faster.
Jon Peltier writes:

January 12, 2012 at 11:39 pm

It makes sense that Len is faster. I read somewhere that VB strings are saved in a compound variable, containing both the length and the characters. Len just extracts the numerical part of the variable.
Jake Heidt writes:

February 15, 2012 at 1:23 pm

Jon,
Yeah they're BSTR's under the covers, which store the length of the allocation before the character bytes. That being said, searching for a null terminator in a char array is not really painful, and there is something (barely) to be said for an extra allocation of 2 bytes per string, not to mention you cap the string length (32767).

If I remember correctly this length prefix was also used in delphi.

BTW, If you havent ever looked at it, check out the ridiculous optimizations they sluethed out in the c standard library implementation of strlen: http://www.stdlib.net/~colmmacc/strlen.c.html