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‎docs/code-quality/ca1834.md

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---
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title: "CA1834: Use StringBuilder.Append(char) for single character strings"
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ms.date: 08/04/2020
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ms.topic: reference
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f1_keywords:
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- "UseStringBuilderAppendChar"
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- "CA1834"
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helpviewer_keywords:
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- "UseStringBuilderAppendChar"
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- "CA1834"
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author: pgovind
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ms.author: prgovi
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manager: jeffhand
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ms.workload:
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- "multiple"
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---
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# CA1834: Use StringBuilder.Append(char) for single character strings
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|Item|Value|
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|-|-|
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|CheckId|CA1834|
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|Category|Microsoft.Performance|
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|Breaking change|Non-breaking|
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## Cause
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This rule fires when a unit length string is passed to the <xref:System.Text.StringBuilder.Append%2A> method.
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## Rule description
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When calling `StringBuilder.Append` with a unit length string, consider using a `const char` rather than a unit length `const string` to improve performance.
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## How to fix violations
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The violation can either be fixed manually, or, in some cases, using Quick Actions to fix code in Visual Studio. Examples:
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##### Example 1
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Invocations of `StringBuilder.Append` with a string literal of unit length:
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```csharp
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using System;
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using System.Text;
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namespace TestNamespace
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{
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class TestClass
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{
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private void TestMethod()
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{
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StringBuilder sb = new StringBuilder();
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sb.Append("a");
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}
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}
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}
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```
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> [!TIP]
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> 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.
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>
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> ![Code fix for CA1834 - Use StringBuilder.Append(char) for single character strings](media/ca1834-codefix.png)
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##### Fix applied by Visual Studio
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```csharp
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using System;
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using System.Text;
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namespace TestNamespace
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{
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class TestClass
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{
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private void TestMethod()
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{
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StringBuilder sb = new StringBuilder();
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sb.Append('a');
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}
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}
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}
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```
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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.
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##### Example 2
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Invocations of `StringBuilder.Append` with a `const string` class field of unit length:
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```cs
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using System;
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using System.Text;
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namespace TestNamespace
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{
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public class Program
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{
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public const string unitString = "a";
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static void Main(string[] args)
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{
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StringBuilder sb = new StringBuilder();
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sb.Append(unitString);
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}
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}
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}
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```
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After careful analysis, `unitString` here can be changed to a `char` without causing any build errors.
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##### Fix
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```cs
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using System;
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using System.Text;
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namespace TestNamespace
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{
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public class Program
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{
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public const char unitString = 'a';
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static void Main(string[] args)
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{
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StringBuilder sb = new StringBuilder();
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sb.Append(unitString);
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}
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}
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}
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```
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## When to suppress warnings
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It's safe to suppress a violation of this rule if you're not concerned about improving performance when using `StringBuilder`.
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## See also
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- [Performance warnings](../code-quality/performance-warnings.md)

‎docs/code-quality/code-analysis-warnings-for-managed-code-by-checkid.md

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- CA1831
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- CA1832
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- CA1833
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- CA1834
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- CA1835
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- CA1836
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- CA1837
@@ -463,7 +464,8 @@ The following table lists Code Analysis warnings for managed code by the CheckId
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| CA1831 |[CA1831: Use AsSpan instead of Range-based indexers for string when appropriate](../code-quality/ca1831.md) | When using a range-indexer on a string and implicitly assigning the value to ReadOnlySpan&lt;char&gt; type, the method <xref:System.String.Substring%2A?#System_String_Substring_System_Int32_System_Int32_> will be used instead of <xref:System.Span%601.Slice%2A?#System_Span_1_Slice_System_Int32_System_Int32_>, which produces a copy of requested portion of the string. |
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| CA1832 |[CA1832: Use AsSpan or AsMemory instead of Range-based indexers for getting ReadOnlySpan or ReadOnlyMemory portion of an array](../code-quality/ca1832.md) | When using a range-indexer on an array and implicitly assigning the value to a <xref:System.ReadOnlySpan%601> or <xref:System.ReadOnlyMemory%601> type, the method <xref:System.Runtime.CompilerServices.RuntimeHelpers.GetSubArray%2A> will be used instead of <xref:System.Span%601.Slice%2A?#System_Span_1_Slice_System_Int32_System_Int32_>, which produces a copy of requested portion of the array. |
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| CA1833 |[CA1833: Use AsSpan or AsMemory instead of Range-based indexers for getting Span or Memory portion of an array](../code-quality/ca1833.md) | When using a range-indexer on an array and implicitly assigning the value to a <xref:System.Span%601> or <xref:System.Memory%601> type, the method <xref:System.Runtime.CompilerServices.RuntimeHelpers.GetSubArray%2A> will be used instead of <xref:System.Span%601.Slice%2A?#System_Span_1_Slice_System_Int32_System_Int32_>, which produces a copy of requested portion of the array. |
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| CA1835 |[CA1835: Prefer the 'Memory'-based overloads for 'ReadAsync' and 'WriteAsync'](../code-quality/ca1835.md) | 'Stream' has a 'ReadAsync' overload that takes a 'Memory&lt;Byte&gt;' as the first argument, and a 'WriteAsync' overload that takes a 'ReadOnlyMemory&lt;Byte&gt;' as the first argument. Prefer calling the memory-based overloads, which are more efficient. |
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| CA1834 |[CA1834: Use StringBuilder.Append(char) for single character strings](../code-quality/ca1834.md) | <xref:System.Text.StringBuilder> has an `Append` overload that takes a `char` as its argument. Prefer calling the `char` overload for performance reasons. |
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| CA1835 |[CA1835: Prefer the 'Memory'-based overloads for 'ReadAsync' and 'WriteAsync'](../code-quality/ca1835.md) | 'Stream' has a 'ReadAsync' overload that takes a 'Memory&lt;Byte&gt;' as the first argument, and a 'WriteAsync' overload that takes a 'ReadOnlyMemory&lt;Byte&gt;' as the first argument. Prefer calling the memory based overloads, which are more efficient. |
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| CA1836 |[CA1836: Prefer `IsEmpty` over `Count` when available](../code-quality/ca1836.md) | Prefer `IsEmpty` property that is more efficient than `Count`, `Length`, <xref:System.Linq.Enumerable.Count%60%601%28System.Collections.Generic.IEnumerable%7B%60%600%7D%29> or <xref:System.Linq.Enumerable.LongCount%60%601%28System.Collections.Generic.IEnumerable%7B%60%600%7D%29> to determine whether the object contains or not any items. |
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| CA1837 | [CA1837: Use `Environment.ProcessId` instead of `Process.GetCurrentProcess().Id`](../code-quality/ca1837.md) | `Environment.ProcessId` is simpler and faster than `Process.GetCurrentProcess().Id`. |
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| CA1838 | [CA1838: Avoid `StringBuilder` parameters for P/Invokes](../code-quality/ca1838.md) | Marshaling of 'StringBuilder' always creates a native buffer copy, resulting in multiple allocations for one marshaling operation. |

‎docs/code-quality/media/ca1834-codefix.png

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‎docs/code-quality/performance-warnings.md

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| [CA1831: Use AsSpan instead of Range-based indexers for string when appropriate](../code-quality/ca1831.md) | When using a range-indexer on a string and implicitly assigning the value to a ReadOnlySpan&lt;char&gt; type, the method <xref:System.String.Substring%2A?#System_String_Substring_System_Int32_System_Int32_> will be used instead of <xref:System.Span%601.Slice%2A?#System_Span_1_Slice_System_Int32_System_Int32_>, which produces a copy of requested portion of the string. |
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| [CA1832: Use AsSpan or AsMemory instead of Range-based indexers for getting ReadOnlySpan or ReadOnlyMemory portion of an array](../code-quality/ca1832.md) | When using a range-indexer on an array and implicitly assigning the value to a <xref:System.ReadOnlySpan%601> or <xref:System.ReadOnlyMemory%601> type, the method <xref:System.Runtime.CompilerServices.RuntimeHelpers.GetSubArray%2A> will be used instead of <xref:System.Span%601.Slice%2A?#System_Span_1_Slice_System_Int32_System_Int32_>, which produces a copy of requested portion of the array. |
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| [CA1833: Use AsSpan or AsMemory instead of Range-based indexers for getting Span or Memory portion of an array](../code-quality/ca1833.md) | When using a range-indexer on an array and implicitly assigning the value to a <xref:System.Span%601> or <xref:System.Memory%601> type, the method <xref:System.Runtime.CompilerServices.RuntimeHelpers.GetSubArray%2A> will be used instead of <xref:System.Span%601.Slice%2A?#System_Span_1_Slice_System_Int32_System_Int32_>, which produces a copy of requested portion of the array. |
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| [CA1834: Use StringBuilder.Append(char) for single character strings](../code-quality/ca1834.md) | <xref:System.Text.StringBuilder> has an `Append` overload that takes a `char` as its argument. Prefer calling the `char` overload to improve performance. |
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| [CA1835: Prefer the 'Memory'-based overloads for 'ReadAsync' and 'WriteAsync'](../code-quality/ca1835.md) | 'Stream' has a 'ReadAsync' overload that takes a 'Memory&lt;Byte&gt;' as the first argument, and a 'WriteAsync' overload that takes a 'ReadOnlyMemory&lt;Byte&gt;' as the first argument. Prefer calling the memory based overloads, which are more efficient. |
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| [CA1836: Prefer `IsEmpty` over `Count` when available](../code-quality/ca1836.md) | Prefer `IsEmpty` property that is more efficient than `Count`, `Length`, <xref:System.Linq.Enumerable.Count%60%601%28System.Collections.Generic.IEnumerable%7B%60%600%7D%29> or <xref:System.Linq.Enumerable.LongCount%60%601%28System.Collections.Generic.IEnumerable%7B%60%600%7D%29> to determine whether the object contains or not any items. |
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| [CA1837: Use `Environment.ProcessId` instead of `Process.GetCurrentProcess().Id`](../code-quality/ca1837.md) | `Environment.ProcessId` is simpler and faster than `Process.GetCurrentProcess().Id`. |

‎docs/code-quality/toc.yml

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href: ca1832.md
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- name: "CA1833: Use AsSpan or AsMemory instead of Range-based indexers for getting Span or Memory portion of an array"
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href: ca1833.md
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- name: "CA1834: Use StringBuilder.Append(char) for single character strings"
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href: ca1834.md
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- name: "CA1835: Prefer the memory overloads of Stream ReadAsync/WriteAsync methods"
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href: ca1835.md
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- name: "CA1836: Prefer IsEmpty over Count when available"

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