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

Value
Rule ID CA1834
Category Performance
Fix is breaking or non-breaking Non-breaking

Cause

This rule fires when a unit length string is passed to the 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");
        }
    }
}

Tip

A code fix is available for this rule in Visual Studio. To use it, position the cursor on the violation and press Ctrl+. (period). Choose Consider using 'StringBuilder.Append(char)' when applicable. from the list of options that is presented.

Code fix for CA1834 - Use StringBuilder.Append(char) for single character strings

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.

See also