CA1872: Prefer 'Convert.ToHexString' and 'Convert.ToHexStringLower' over call chains based on 'BitConverter.ToString'

Article
10/30/2024

	Value
Rule ID	CA1872
Title	Prefer `Convert.ToHexString` and `Convert.ToHexStringLower` over call chains based on `BitConverter.ToString`
Category	Performance
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 9	As suggestion

Cause

A call to BitConverter.ToString followed by a call to String.Replace to remove dashes is used to encode bytes to a hexadecimal string representation. This rule also fires if String.ToLower is used in the call chain.

Rule description

Use Convert.ToHexString or Convert.ToHexStringLower when encoding bytes to a hexadecimal string representation. These methods are more efficient and allocation-friendly than using BitConverter.ToString in combination with String.Replace to remove dashes and String.ToLower.

How to fix violations

To fix a violation of this rule, replace the call chain with either Convert.ToHexString or Convert.ToHexStringLower.

Example

The following code snippet shows a violation of CA1872:

using System;
using System.Text;

class HelloWorldEncoder
{
    private readonly byte[] _data = Encoding.ASCII.GetBytes("Hello World");

    public string Encode()
    {
        return BitConverter.ToString(_data).Replace("-", "");
    }

    public string EncodeToLower()
    {
        return BitConverter.ToString(_data).Replace("-", "").ToLower();
    }
}

Imports System
Imports System.Text

Class HelloWorldEncoder
    Private ReadOnly _data As Byte() = Encoding.ASCII.GetBytes("Hello World")

    Public Function Encode() As String
        Return BitConverter.ToString(_data).Replace("-", "")
    End Function

    Public Function EncodeToLower() As String
        Return BitConverter.ToString(_data).Replace("-", "").ToLower()
    End Function
End Class

The following code snippet fixes the violation:

using System;
using System.Text;

class HelloWorldEncoder
{
    private readonly byte[] _data = Encoding.ASCII.GetBytes("Hello World");

    public string Encode()
    {
        return Convert.ToHexString(_data);
    }

    public string EncodeToLower()
    {
        return Convert.ToHexStringLower(_data);
    }
}

Imports System
Imports System.Text

Class HelloWorldEncoder
    Private ReadOnly _data As Byte() = Encoding.ASCII.GetBytes("Hello World")

    Public Function Encode() As String
        Return Convert.ToHexString(_data)
    End Function

    Public Function EncodeToLower() As String
        Return Convert.ToHexStringLower(_data)
    End Function
End Class

When to suppress warnings

It is safe to suppress a warning from this rule; however, we recommend that you use either Convert.ToHexString or Convert.ToHexStringLower.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1872
// The code that's violating the rule is on this line.
#pragma warning restore CA1872

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1872.severity = none

For more information, see How to suppress code analysis warnings.

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