Why is this an issue?
It is important to be careful when searching for characters within a substring. Let’s consider the following example:
if (str.SubString(startIndex).IndexOf(char1) == -1) // Noncompliant: a new string is going to be created by "Substring"
{
// ...
}
A new string object is created with every call to the Substring method. When chaining it with any of the
following methods, it creates a new object for one-time use only:
What is the potential impact?
Creating a new object consumes significant system resources, especially CPU and memory.
When using Substring repeatedly, such as in a loop, it can greatly impact the overall performance of the application or program.
To mitigate the creation of new objects while searching for characters within a substring, it is possible to use an overload of the mentioned
methods with a startIndex parameter:
if (str.IndexOf(char1, startIndex) == -1) // Compliant: no new instance of string is created
{
// ...
}
Using these methods gives the same result while avoiding the creation of additional string objects.
Resources
Documentation
Benchmarks
| Method |
Runtime |
StringSize |
Mean |
StdDev |
Ratio |
Allocated |
SubstringThenIndexOf |
.NET 7.0 |
10 |
11.234 ms |
0.1319 ms |
1.00 |
40000008 B |
IndexOfOnly |
.NET 7.0 |
10 |
2.477 ms |
0.0473 ms |
0.22 |
2 B |
SubstringThenIndexOf |
.NET Framework 4.6.2 |
10 |
8.634 ms |
0.4195 ms |
1.00 |
48141349 B |
IndexOfOnly |
.NET Framework 4.6.2 |
10 |
1.724 ms |
0.0346 ms |
0.19 |
- |
SubstringThenIndexOf |
.NET 7.0 |
100 |
14.651 ms |
0.2977 ms |
1.00 |
176000008 B |
IndexOfOnly |
.NET 7.0 |
100 |
2.464 ms |
0.0501 ms |
0.17 |
2 B |
SubstringThenIndexOf |
.NET Framework 4.6.2 |
100 |
13.363 ms |
0.2044 ms |
1.00 |
176518761 B |
IndexOfOnly |
.NET Framework 4.6.2 |
100 |
1.689 ms |
0.0290 ms |
0.13 |
- |
SubstringThenIndexOf |
.NET 7.0 |
1000 |
78.688 ms |
2.4727 ms |
1.00 |
1528000072 B |
IndexOfOnly |
.NET 7.0 |
1000 |
2.456 ms |
0.0397 ms |
0.03 |
2 B |
SubstringThenIndexOf |
.NET Framework 4.6.2 |
1000 |
75.994 ms |
1.2650 ms |
1.00 |
1532637240 B |
IndexOfOnly |
.NET Framework 4.6.2 |
1000 |
1.699 ms |
0.0216 ms |
0.02 |
- |
The results were generated by running the following snippet with BenchmarkDotNet:
private string theString;
private int iteration = 1_000_000;
[Params(10, 100, 1_000)]
public int StringSize { get; set; }
[GlobalSetup]
public void Setup() =>
theString = new string('a', StringSize);
[Benchmark(Baseline = true)]
public void SubstringThenIndexOf()
{
for (var i = 0; i < iteration; i++)
{
_ = theString.Substring(StringSize / 4).IndexOf('a');
}
}
[Benchmark]
public void IndexOfOnly()
{
for (var i = 0; i < iteration; i++)
{
_ = theString.IndexOf('a', StringSize / 4) - StringSize / 4;
}
}
Hardware configuration:
BenchmarkDotNet=v0.13.5, OS=Windows 10 (10.0.19045.2965/22H2/2022Update)
12th Gen Intel Core i7-12800H, 1 CPU, 20 logical and 14 physical cores
.NET SDK=7.0.203
[Host] : .NET 7.0.5 (7.0.523.17405), X64 RyuJIT AVX2
.NET 7.0 : .NET 7.0.5 (7.0.523.17405), X64 RyuJIT AVX2
.NET Framework 4.6.2 : .NET Framework 4.8 (4.8.4614.0), X64 RyuJIT VectorSize=256
