org.sonar.plugins.csharp.S4635.html Maven / Gradle / Ivy
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
-
String.Substring Method
-
String.IndexOf Method
-
String.IndexOfAny Method
-
String.LastIndexOf Method
-
String.LastIndexOfAny Method
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