CA1834: Use StringBuilder.Append(char) for single character strings

#Cause

This rule fires when a unit length string is passed to the System.Text.StringBuilder.Append method.

#Rule description

When calling StringBuilder.Append with a unit length string, consider using a const char rather than a unit length const string to improve performance.

#How to fix violations

The violation can either be fixed manually, or, in some cases, using Quick Actions to fix code in Visual Studio. Examples:

#Example 1

Invocations of StringBuilder.Append with a string literal of unit length:

using System;
using System.Text;

namespace TestNamespace
{
    class TestClass
    {
        private void TestMethod()
        {
            StringBuilder sb = new StringBuilder();
            sb.Append("a");
        }
    }
}

Fix applied by Visual Studio:

using System;
using System.Text;

namespace TestNamespace
{
    class TestClass
    {
        private void TestMethod()
        {
            StringBuilder sb = new StringBuilder();
            sb.Append('a');
        }
    }
}

In some cases, for example when using a unit length const string class field, a code-fix is not suggested by Visual Studio (but the analyzer still fires). These instances require a manual fix.

#Example 2

Invocations of StringBuilder.Append with a const string class field of unit length:

using System;
using System.Text;

namespace TestNamespace
{
    public class Program
    {
        public const string unitString = "a";

        static void Main(string[] args)
        {
            StringBuilder sb = new StringBuilder();
            sb.Append(unitString);
        }
    }
}

After careful analysis, unitString here can be changed to a char without causing any build errors.

using System;
using System.Text;

namespace TestNamespace
{
    public class Program
    {
        public const char unitString = 'a';

        static void Main(string[] args)
        {
            StringBuilder sb = new StringBuilder();
            sb.Append(unitString);
        }
    }
}

#When to suppress warnings

It's safe to suppress a violation of this rule if you're not concerned about improving performance when using StringBuilder.

#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 CA1834
// The code that's violating the rule is on this line.
#pragma warning restore CA1834

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

[*.{cs,vb}]
dotnet_diagnostic.CA1834.severity = none

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

#See also

• Performance rules