Does string.IsNullOrEmpty have performance issues?

Question

Is there any difference between this two ways of checking the string?

if(!string.IsNullOrEmpty(myString))
{
  //Do something
}

and

if(myString != null && myString != "")
{
  //Do something
}

So far I though no, but someone is saying so. And he's saying that the second one is better as the first one requires a method call.

I'm a little confused.

Run some benchmarks. Do both at least 100,000 times, several times and measure the performance. See which one is quicker). — ChrisF, Aug 26 '13 at 14:48
http://stackoverflow.com/questions/10360370/why-is-string-isnullorempty-faster-than-string-length take a look here. — priehl, Aug 26 '13 at 14:48
And run those benchmarks in Release mode, if you do it in Debug it won't mean anything. — Pierre-Luc Pineault, Aug 26 '13 at 14:49
Has this person heard of inlining, and given a reason why it doesn't apply here? No? Then it's probably not even worth benchmarking, chances are they have no idea what they're talking about. — , Aug 26 '13 at 14:49
@ChrisF I like the question though. I think it's good that these kind of questions pop up at SO. People read it and can alter code if necessary. I'm guessing you don't have to tell him he just has to do benchmarks, nor others wanting to respond on this. I hope you didn't mean your comment to sound like "Do it yourself"... — Joetjah, Aug 26 '13 at 14:51
`the first one requires a method call` The second one requires method call as well, but it is done by IsNullOrEmpty function. — Alex F, Aug 26 '13 at 14:52
@Joetjah - I take your point, but this could be a good question if it showed that the OP *had* done some tests and found something they didn't understand. — ChrisF, Aug 26 '13 at 14:53
If this did make a difference it would be a micro optimization at best, you shouldn't harm the readability and maintainability of your program for the sake of a micro optimization unless your profiling software tells you that it's a major problem. In all likelihood you'll have much bigger problems than this in terms of performance. — Doctor Jones, Aug 27 '13 at 08:45
@ChrisF I get your point about the guy not doing research, but the question has value. Some people don't have the knowledge or experience to know where to start researching a problem, we shouldn't penalise entry level programmers unless it's a dupe or very low quality. I think this is an interesting and informative question/answer thread. — Doctor Jones, Aug 27 '13 at 08:47

score 15 · Answer 1 · answered Aug 26 '13 at 14:48

15

No, there are no performance problems with it. Here's how it is implemented:

public static bool IsNullOrEmpty(string value)
{
    if (value != null)
    {
        return (value.Length == 0);
    }
    return true;
}

I would use always use IsNullOrEmpty instead of writing the 2 conditions manually. It's much more readable and there is no performance cost associated to using it.

answered Aug 26 '13 at 14:48

Darin Dimitrov

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Plus the fact that it's very likely to be inlined. It's probably important to mention it, because it means there is no overhead due to the method call. – Thomas Levesque Aug 26 '13 at 14:50
There's is actually a difference; see the benchmark in my answer. – Thomas Levesque Aug 26 '13 at 15:48
Yes, that is why IsNullOrEmpty is faster than == "" – Vasil Popov Oct 15 '13 at 08:10

Thomas Levesque · Accepted Answer · 2013-08-26T19:58:22.857

Like every one else who answered, I assumed there would be no performance difference, but I ran a benchmark just to be sure. The results are not exactly what I expected...

Here's the code for my benchmark:

using System;
using System.Diagnostics;

static class Program
{
    static void Main()
    {
        int count = 1;

        // First run for JIT warm-up
        IsNullOrEmpty(null, count);
        TestEqualsEmpty(null, count);
        TestLengthZero(null, count);

        count = 1000000000;

        Console.WriteLine("Case 1: s == \"test\"");
        RunTests("test", count);

        Console.WriteLine("Case 2: s == null");
        RunTests(null, count);

        Console.WriteLine("Case 3: s == \"\"");
        RunTests("", count);
    }

    static void RunTests(string s, int count)
    {
        var ts = IsNullOrEmpty(s, count);
        Console.WriteLine("\tIsNullOrEmpty:         {0}", ts);

        ts = TestLengthZero(s, count);
        Console.WriteLine("\tTest if s.Length == 0: {0}", ts);

        ts = TestEqualsEmpty(s, count);
        Console.WriteLine("\tTest if s == \"\":       {0}", ts);
    }

    static TimeSpan IsNullOrEmpty(string s, int count)
    {
        var sw = Stopwatch.StartNew();
        for (int i = 0; i < count; i++)
        {
            if (string.IsNullOrEmpty(s))
            {
            }
        }
        sw.Stop();
        return sw.Elapsed;
    }

    static TimeSpan TestLengthZero(string s, int count)
    {
        var sw = Stopwatch.StartNew();
        for (int i = 0; i < count; i++)
        {
            if (s == null || s.Length == 0)
            {
            }
        }
        sw.Stop();
        return sw.Elapsed;
    }

    static TimeSpan TestEqualsEmpty(string s, int count)
    {
        var sw = Stopwatch.StartNew();
        for (int i = 0; i < count; i++)
        {
            if (s == null || s == "")
            {
            }
        }
        sw.Stop();
        return sw.Elapsed;
    }
}

And here are the results:

Case 1: s == "test"
        IsNullOrEmpty:         00:00:00.6000748
        Test if s.Length == 0: 00:00:00.5566793
        Test if s == "":       00:00:02.2284007
Case 2: s == null
        IsNullOrEmpty:         00:00:00.5556170
        Test if s.Length == 0: 00:00:00.5569102
        Test if s == "":       00:00:00.5554338
Case 3: s == ""
        IsNullOrEmpty:         00:00:00.5568344
        Test if s.Length == 0: 00:00:00.5556285
        Test if s == "":       00:00:03.0626445

(compiled with optimisations enabled; these are the results with the 32-bit CLR, but the results are similar for the 64-bit CLR)

So as you can see, if the string is not null, calling IsNullOrEmpty is much faster than comparing with null and "", and almost as fast as comparing with null and testing if the length is 0. If the string is null, all 3 methods have identical performance.

So, doing this:

if(myString != null && myString != "")

is probably going to be slower, not faster, than this:

if(string.IsNullOrEmpty(myString))

You could do this:

if(myString != null && myString.Length > 0)

but the performance gain would be very small compared to calling IsNullOrEmpty, and it would harm readability.

Note that this benchmark was run with 1,000,000,000 (1 billion) iterations; this was necessary to notice an actual difference. In a real-world scenario, the difference would probably be to small to notice; this is clearly a micro-optimisation.

Actually, this is exactly what I expected. Just think about it, if you compared against null or length, those are some comparisons (since length is also stored). String comparision is a more generalized thing. Depending upon compiler settings and runtime version, I would expect the compiler could perform the optimization against a hard coded string, not that it would necessarily do so. — Gary Walker, Aug 26 '13 at 16:38
Have you verified that the compiler doesn't remove the tests? After all you are not doing anything, so if the comparison doesn't have any side effect the entire block can safely be optimized away (I don't know if it does though). — Brian Rasmussen, Aug 26 '13 at 16:58
@BrianRasmussen, good point; I just checked with ildasm, the tests are not removed in the IL. I don't know if the JIT does this kind of optimization, though... — Thomas Levesque, Aug 26 '13 at 20:02
If you check the String.cs source file of the .Net framework, you will see that IsNullOrEmpty does not checks for == "" because it is slow, it checks .Length == 0! That is why the results of your benchmark are what you did not expected. :) The correct answer for me is of Darin Dimitrov. — Vasil Popov, Oct 15 '13 at 08:09
00:00:00.5566793 and 00:00:00.6000748 for the first sample can't be treated as significantly important and prove that there is a difference. Tests should be run in a different order, multiple times and we should take the average between tests. — Seagull, Aug 20 '19 at 14:55
Case 1: s == "test" IsNullOrEmpty: 00:00:03.1741938 Test if s.Length == 0: 00:00:04.2489601 Test if s == "": 00:00:05.0501413 Case 2: s == null IsNullOrEmpty: 00:00:02.9983790 Test if s.Length == 0: 00:00:02.6700504 Test if s == "": 00:00:02.6707513 Case 3: s == "" IsNullOrEmpty: 00:00:03.0292318 Test if s.Length == 0: 00:00:04.7712468 Test if s == "": 00:00:04.8452256 — Salvuccino, Oct 13 '21 at 15:17

score 5 · Answer 3 · edited Aug 27 '13 at 08:39

I would say even if IsNullOrEmpty a bit slow then also use it because it is much less confusing and much more readable then using strange IF conditions.

See following example

if((!string.IsNullOrEmpty(str1)) && (!string.IsNullOrEmpty(str2)) && (!string.IsNullOrEmpty(str3)))
{
//Code here
}

is much more readable then following

if(str1 != null && str1 != "" && str2 != null && str2 != "" && str3 != null && str3 != "")
{
// Code here
}

score 4 · Answer 4 · answered Aug 26 '13 at 14:51

Your current code is fine, and you shouldn't have any performance difference.

Currently it is implemented as:

 public static bool IsNullOrEmpty(String value) 
 {
     return (value == null || value.Length == 0);
 }

Source code take from HERE

If there is going to be a difference in performance then it must be negligible. You should always consider code that is more readable for cases like these.

You may also see: Premature-Optimization and Performance Anxiety

score 1 · Answer 5 · answered Aug 26 '13 at 14:51

1

If you look for response times on execution, you can see 'Alternatives' section on http://www.dotnetperls.com/isnullorempty.

I also think, that the IsNullOrEmpty method way is cleaner than other ways.

answered Aug 26 '13 at 14:51

Pato

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score 1 · Answer 6 · answered Aug 26 '13 at 14:53

http://blogs.msdn.com/b/ericgu/archive/2004/01/29/64717.aspx -- This describes has CLR functions are automatically inlined. Just because you profile it today and see a difference does not mean it will be the same the next time you run it. If you are really concerned about performance, you avoid the potential function call as you explicitly inlined it by hand. Really though, save such micro-optimizations till you profile it and see you have a need.

A future version of .Net could also Change the implementation of IsNullOrEmpty() to be an optimized native code call.

score 0 · Answer 7 · answered Aug 26 '13 at 14:55

0

When you call a function, extra assembly instructions are used to put another stack frame on the call stack. One method of optimization is to remove all these redundant calls and replace them with inline code (as that "someone" recommends). However, optimizations at this level are almost never necessary.

This difference in speed is basically unmeasurable with only a single call. Readable code, like yours, should always be valued over unnecessary optimizations.

answered Aug 26 '13 at 14:55

twinlakes

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The inlining optimizations are performed for you by the compiler and the JIT. They will almost always be better at it than you are. – Avner Shahar-Kashtan Aug 26 '13 at 15:04

Does string.IsNullOrEmpty have performance issues?

7 Answers7