Strings are one of the most commonly used types in .NET applications - and very often the source of inefficient code. For example, cleaning up a string - such as removing invalid or non-visible characters - is one of the most common use cases for user input. Unfortunately, the most convenient, but not the most efficient, implementation imaginable is used in this case: Linq.
See full sample here: Sustainable Code by BEN ABT on GitHub
String Manipulation
The most inefficient option, as already mentioned, is direct string manipulation with Linq. Unfortunately, I see this variant by far the most.
string.Concat(source.Where(c => char.IsControl(c) is false))1| Method | Runtime | Mean | Ratio | RatioSD | Gen0 | Gen1 | Allocated | Alloc Ratio |
2|----------------------- |--------- |-----------:|------:|--------:|-------:|-------:|----------:|------------:|
3| Linq | .NET 8.0 | 1,646.5 ns | 3.47 | 0.03 | 0.0782 | - | 1.3 KB | 1.07 |String Builder
The StringBuilder is significantly faster, as it works directly on the memory area of the string and is therefore very efficient.
1StringBuilder sb = new();
2
3foreach (char c in source)
4{
5 if (char.IsControl(c) is false)
6 {
7 sb.Append(c);
8 }
9}
10
11return sb.ToString();1| Method | Runtime | Mean | Ratio | RatioSD | Gen0 | Gen1 | Allocated | Alloc Ratio |
2|----------------------- |--------- |-----------:|------:|--------:|-------:|-------:|----------:|------------:|
3| StringBuilder_Instance | .NET 8.0 | 860.0 ns | 1.81 | 0.02 | 0.2270 | 0.0019 | 3.71 KB | 3.04 |The disadvantage at this point is that the StringBuilder must be initialized in addition to the actual operation, which is why we also have an additional Gen1 allocation. However, this disadvantage can be optimized by pooling, so that this takes about 15% less time than the instance variant and about 50% less than the Linq variant.
1| Method | Runtime | Mean | Ratio | RatioSD | Gen0 | Gen1 | Allocated | Alloc Ratio |
2|----------------------- |--------- |-----------:|------:|--------:|-------:|-------:|----------:|------------:|
3| StringBuilder_Pool | .NET 8.0 | 706.2 ns | 1.49 | 0.02 | 0.0744 | - | 1.22 KB | 1.00 |Span
The span implementation has been available in .NET for almost seven years, but it is still often not used. Admittedly, the barrier to entry of understanding Span and the somewhat “low level” approach doesn’t make it easy, but the results speak for themselves.
The four different span implementations are all faster and more efficient by a large margin; led by an unsafe implementation, which however cannot be used in all scenarios; for example when unsafe code blocks are not possible or allowed.
1| Method | Runtime | Mean | Ratio | RatioSD | Gen0 | Gen1 | Allocated | Alloc Ratio |
2|----------------------- |--------- |-----------:|------:|--------:|-------:|-------:|----------:|------------:|
3| Span | .NET 8.0 | 394.4 ns | 0.83 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 |
4| Span1 | .NET 8.0 | 474.7 ns | 1.00 | 0.00 | 0.0744 | - | 1.22 KB | 1.00 |
5| Span2 | .NET 8.0 | 411.8 ns | 0.87 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 |
6| Span2Unsafe | .NET 8.0 | 375.1 ns | 0.79 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 | 1public static string UsingSpan(string source)
2{
3 int length = source.Length;
4 char[]? rentedFromPool = null;
5
6 // allocate
7 Span<char> buffer = length > 512 ?
8 (rentedFromPool = ArrayPool<char>.Shared.Rent(length)) : (stackalloc char[512]);
9
10 // filter
11 int index = 0;
12 foreach (char c in source)
13 {
14 if (char.IsControl(c) is false)
15 {
16 buffer[index] = c;
17 index++;
18 }
19 }
20
21 // only return the data that was written
22 string data = buffer.Slice(0, index).ToString();
23
24 // cleanup
25 if (rentedFromPool is not null)
26 {
27 ArrayPool<char>.Shared.Return(rentedFromPool, clearArray: true);
28 }
29
30 return data;
31}Sustainable Code
Sustainable code is becoming increasingly important - this should not be neglected, especially in migration projects. This is the best opportunity to implement sustainable code from the ground up.
You can find the complete example of how to clean up strings efficiently here and more examples of sustainable implementation of everyday code with C# and .NET under https://github.com/BenjaminAbt/SustainableCode .
1BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.4412/22H2/2022Update)
2AMD Ryzen 9 5950X, 1 CPU, 32 logical and 16 physical cores
3.NET SDK 9.0.100-preview.3.24204.13
4 [Host] : .NET 8.0.5 (8.0.524.21615), X64 RyuJIT AVX2
5 .NET 8.0 : .NET 8.0.5 (8.0.524.21615), X64 RyuJIT AVX2
6 .NET 9.0 : .NET 9.0.0 (9.0.24.17209), X64 RyuJIT AVX2
7
8
9| Method | Runtime | Mean | Ratio | RatioSD | Gen0 | Gen1 | Allocated | Alloc Ratio |
10|----------------------- |--------- |-----------:|------:|--------:|-------:|-------:|----------:|------------:|
11| StringBuilder_Pool | .NET 8.0 | 706.2 ns | 1.49 | 0.02 | 0.0744 | - | 1.22 KB | 1.00 |
12| StringBuilder_Instance | .NET 8.0 | 860.0 ns | 1.81 | 0.02 | 0.2270 | 0.0019 | 3.71 KB | 3.04 |
13| Linq | .NET 8.0 | 1,646.5 ns | 3.47 | 0.03 | 0.0782 | - | 1.3 KB | 1.07 |
14| Span | .NET 8.0 | 394.4 ns | 0.83 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 |
15| Span1 | .NET 8.0 | 474.7 ns | 1.00 | 0.00 | 0.0744 | - | 1.22 KB | 1.00 |
16| Span2 | .NET 8.0 | 411.8 ns | 0.87 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 |
17| Span2Unsafe | .NET 8.0 | 375.1 ns | 0.79 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 |
18| | | | | | | | | |
19| StringBuilder_Pool | .NET 9.0 | 616.3 ns | 1.19 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 |
20| StringBuilder_Instance | .NET 9.0 | 715.9 ns | 1.39 | 0.01 | 0.2270 | 0.0019 | 3.71 KB | 3.04 |
21| Linq | .NET 9.0 | 1,663.5 ns | 3.22 | 0.02 | 0.0782 | - | 1.3 KB | 1.07 |
22| Span | .NET 9.0 | 404.9 ns | 0.78 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 |
23| Span1 | .NET 9.0 | 516.1 ns | 1.00 | 0.00 | 0.0744 | - | 1.22 KB | 1.00 |
24| Span2 | .NET 9.0 | 398.9 ns | 0.77 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 |
25| Span2Unsafe | .NET 9.0 | 389.4 ns | 0.75 | 0.01 | 0.0744 | - | 1.22 KB | 1.00 |Related articles
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BEN ABT
Ben is Chief Engineering Officer and Principal Software Engineer at Medialesson.de, with a strong focus on .NET and Microsoft Azure. In his professional role, he designs and builds highly scalable platforms for hybrid and cloud-based scenarios. He also advises companies and C-levels on migrating to the sovereign cloud.
He runs myCSharp.de, the largest and most active German-speaking C# community forum, actively contributes to both his own and external open-source projects and regularly shares his knowledge through his blog, at community events, conferences and as a writer for technical magazines.
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