Merge pull request #2844 from dmitrykobets/dmitrykobets-patch-2

American-Dipper · web-flow · commit 288739ccbc1c · 2020-04-23T15:43:36.000-07:00
Create c26819.md
diff --git a/docs/code-quality/c26819.md b/docs/code-quality/c26819.md
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+---
+title: C26819
+description: "Reference for Microsoft C++ Code Analysis warning C26819 in Visual Studio."
+ms.date: 04/22/2020
+ms.topic: "reference"
+f1_keywords: ["C26819"]
+helpviewer_keywords: ["C26819"]
+---
+# C26819
+
+> Unannotated fallthrough between switch labels (es.78).
+
+## Remarks
+
+This check covers implicit fallthrough in switch statements. Implicit fallthrough is when control flow transfers from one switch case directly into a following switch case without the use of the `[[fallthrough]];` statement. This warning is raised when an implicit fallthrough is detected in a switch case containing at least one statement.
+
+For more information, see [ES.78: Don't rely on implicit fallthrough in `switch` statements](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-break) in the C++ Core Guidelines.
+
+## Example
+
+In this sample, implicit fallthrough occurs from a non-empty switch case into a following case.
+
+```cpp
+void fn1();
+void fn2();
+
+void foo(int a)
+{
+    switch (a)
+    {
+        case 0: // implicit fallthrough from case 0 to case 1 is OK because case 0 is empty
+        case 1:
+            fn1(); // implicit fallthrough from case 1 into case 2
+        case 2:
+            fn2();
+            break;
+        default:
+            break;
+    }
+}
+```
+
+## Solution
+
+To fix this issue, insert a `[[fallthrough]];` statement where the fallthrough occurs.
+
+```cpp
+void fn1();
+void fn2();
+
+void foo(int a)
+{
+    switch (a)
+    {
+        case 0:
+        case 1:
+            fn1();
+            [[fallthrough]]; // fallthrough is explicit
+        case 2:
+            fn2();
+            break;
+        default:
+            break;
+    }
+}
+```
+
+Another way to fix the issue is to remove the implicit fallthrough.
+
+```cpp
+void fn1();
+void fn2();
+
+void foo(int a)
+{
+    switch (a)
+    {
+        case 0:
+        case 1:
+            fn1();
+            break; // case 1 no longer falls through into case 2
+        case 2:
+            fn2();
+            break;
+        default:
+            break;
+    }
+}
+```
