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Add warning C4388, update 16.7 warnings
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‎docs/error-messages/compiler-warnings/c4388.md

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---
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title: "Compiler Warning (level 4) C4388"
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description: "Microsoft C/C++ compiler warning C4388, its causes and resolution."
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ms.date: 10/16/2020
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f1_keywords: ["C4388"]
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helpviewer_keywords: ["C4388"]
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---
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# Compiler Warning (level 4) C4388
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> '*token*' : signed/unsigned mismatch
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Using the *token* operator to compare a **`signed`** and a larger **`unsigned`** number required the compiler to convert the **`signed`** value to the larger **`unsigned`** type.
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## Remarks
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One way to fix this warning is if you cast one of the two types when you compare **`signed`** and larger **`unsigned`** types.
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This warning is off by default. You can use [/Wall](../../build/reference/compiler-option-warning-level.md) or **`/w44388`** to enable it on the command line as a level 4 warning. Or, use [`#pragma warning(default:4388)`](../../preprocessor/warning.md) in your source file. For more information, see [Compiler warnings that are off by default](../../preprocessor/compiler-warnings-that-are-off-by-default.md).
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## Example
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This sample generates C4388 and shows how to fix it:
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```cpp
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// C4388.cpp
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// compile with: cl /EHsc /W4 C4388.cpp
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#pragma warning(default: 4388)
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int main() {
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unsigned long long uc = 0;
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int c = 0;
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unsigned long long c2 = c; // implicit conversion
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if (uc < c) // C4388
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uc = 0;
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if (uc < (unsigned long long)(c)) // OK
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uc = 0;
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if (uc < c2) // Also OK
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uc = 0;
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}
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```
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## See also
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[Compiler Warning (Level 3) C4018](compiler-warning-level-3-c4018.md)\
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[Compiler Warning (Level 4) C4389](compiler-warning-level-4-c4389.md)

‎docs/error-messages/compiler-warnings/compiler-warning-level-3-c4018.md

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---
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title: "Compiler Warning (level 3) C4018"
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ms.date: "11/04/2016"
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description: "Microsoft C/C++ compiler warning C4018, its causes and resolution."
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ms.date: 10/16/2020
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f1_keywords: ["C4018"]
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helpviewer_keywords: ["C4018"]
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ms.assetid: 6e8cbb04-d914-4319-b431-cbc2fbe40eb1
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---
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# Compiler Warning (level 3) C4018
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'expression' : signed/unsigned mismatch
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> '*token*' : signed/unsigned mismatch
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Comparing a signed and unsigned number required the compiler to convert the signed value to unsigned.
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Using the *token* operator to compare **`signed`** and **`unsigned`** numbers required the compiler to convert the **`signed`** value to **`unsigned`**.
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This warning may be fixed if you cast one of the two types when testing signed and unsigned types.
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## Remarks
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The following sample generates C4018:
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One way to fix this warning is if you cast one of the two types when you compare **`signed`** and **`unsigned`** types.
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## Example
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This sample generates C4018 and shows how to fix it:
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```cpp
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// C4018.cpp
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// compile with: /W3
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// compile with: cl /EHsc /W4 C4018.cpp
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int main() {
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unsigned int uc = 0;
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int c = 0;
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unsigned int c2 = 0;
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unsigned int uc = 0;
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int c = 0;
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unsigned int c2 = c; // implicit conversion
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if (uc < c) // C4018
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uc = 0;
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if (uc < c) uc = 0; // C4018
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if (uc < unsigned(c)) // OK
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uc = 0;
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// OK
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if (uc == c2) uc = 0;
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if (uc < c2) // Also OK
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uc = 0;
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}
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```
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## See also
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[Compiler Warning (Level 4) C4388](c4388.md)\
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[Compiler Warning (Level 4) C4389](compiler-warning-level-4-c4389.md)

‎docs/error-messages/compiler-warnings/compiler-warning-level-4-c4389.md

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---
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title: "Compiler Warning (level 4) C4389"
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ms.date: "11/04/2016"
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description: "Microsoft C/C++ compiler warning C4389, its causes and resolution."
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ms.date: 10/16/2020
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f1_keywords: ["c4389"]
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helpviewer_keywords: ["C4389"]
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ms.assetid: fc0e3a8e-f766-437c-b7f1-e61abb2a8765
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---
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# Compiler Warning (level 4) C4389
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'operator' : signed/unsigned mismatch
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> '*equality-operator*' : signed/unsigned mismatch
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An operation involved signed and unsigned variables. This could result in a loss of data.
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An **`==`** or **`!=`** operation involved **`signed`** and **`unsigned`** variables. This could result in a loss of data.
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## Remarks
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One way to fix this warning is if you cast one of the two types when you compare **`signed`** and **`unsigned`** types.
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## Example
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The following sample generates C4389:
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```cpp
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// C4389.cpp
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// compile with: /W4
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#pragma warning(default: 4389)
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// compile with: cl /EHsc /W4 C4389.cpp
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int main()
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{
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int a = 9;
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unsigned int b = 10;
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int result = 0;
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if (a == b) // C4389
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return 0;
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result = 1;
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else
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return 0;
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};
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result = 2;
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if (unsigned(a) == b) // OK
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result = 3;
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else
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result = 4;
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return result;
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}
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```
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## See also
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[Compiler Warning C4018](compiler-warning-level-3-c4018.md)\
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[Compiler Warning (Level 4) C4388](c4388.md)

‎docs/error-messages/compiler-warnings/compiler-warnings-by-compiler-version.md

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---
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title: "Compiler Warnings by compiler version"
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ms.date: "04/22/2019"
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description: "Table of Microsoft C/C++ compiler warnings by compiler version."
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ms.date: 10/18/2020
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helpviewer_keywords: ["warnings, by compiler version", "cl.exe compiler, setting warning options"]
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---
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# Compiler Warnings by compiler version
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| Visual Studio 2019 version 16.4 | 19.24.28314.0 |
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| Visual Studio 2019 version 16.5 | 19.25.28610.0 |
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| Visual Studio 2019 version 16.6 | 19.26.28805.0 |
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| Visual Studio 2019 version 16.7 | 19.26.29112.0 |
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You can specify only the major number, the major and minor numbers, or the major, minor, and build numbers to the **`/Wv`** option. The compiler reports all warnings that match versions that begin with the specified number. It suppresses all warnings for versions greater than the specified number. For example, **`/Wv:17`** reports warnings introduced in or before any version of Visual Studio 2012, and suppresses warnings introduced by any compiler from Visual Studio 2013 (version 18) or later. To suppress warnings introduced in Visual Studio 2015 update 2 and later, you can use **`/Wv:19.00.23506`**. Use **`/Wv:19.11`** to report the warnings introduced in any version of Visual Studio before Visual Studio 2017 version 15.5, but suppress warnings introduced in Visual Studio 2017 version 15.5 and later.
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The following sections list the warnings introduced by each version of Visual C++ that you can suppress by using the **`/Wv`** compiler option. The **`/Wv`** option can't suppress warnings that aren't listed, which predate the specified versions of the compiler.
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::: moniker range=">= vs-2019"
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## Warnings introduced in Visual Studio 2019 version 16.7 (compiler version 19.27.29112.0)
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These warnings and all warnings in later versions are suppressed by using the compiler option **`/Wv:19.26`**.
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| Warning | Message |
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|--|--|
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| C5207 | `the simple requirement asserts the validity of expression 'e->id'. Did you mean '{ e } -> id'? You can suppress the warning using '{ e->id }'` |
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| C5209 | `the C++20 syntax for an init-capture has changed to '& ...opt identifier initializer'` |
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| C5210 | `'name' is not a valid header unit reference; ignoring` |
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| C5212 | `'name' is not a valid named reference; treating as reference to file` |
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| C5213 | `'name' named reference is treated as a named partition but the name is not specified; treating as reference to file` |
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| C5214 | `applying 'modifier' to an operand with a volatile qualified type is deprecated in C++20` |
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| C5215 | `'name' a function parameter with a volatile qualified type is deprecated in C++20` |
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| C5216 | `'name' a volatile qualified return type is deprecated in C++20` |
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| C5217 | `a structured binding declaration that includes volatile is deprecated in C++20` |
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| C5218 | `destroying delete may not behave as intended when non-conforming switches '/Zc:sizedDealloc-' or '/Zc:alignedNew-' are used` |
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| C5219 | `implicit conversion from 'type-1' to 'type-2', possible loss of data` |
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| C5220 | `'name': a non-static data member with a volatile qualified type no longer implies%$N that compiler generated copy/move constructors and copy/move assignment operators are not trivial` |
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| C5221 | `xfg::rename is deprecated.` |
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## Warnings introduced in Visual Studio 2019 version 16.6 (compiler version 19.26.28805.0)
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These warnings and all warnings in later versions are suppressed by using the compiler option **`/Wv:19.25`**.

‎docs/error-messages/compiler-warnings/compiler-warnings-c4200-through-c4399.md

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---
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title: "Compiler warnings C4200 Through C4399"
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ms.date: "04/21/2019"
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f1_keywords: ["C4203", "C4277", "C4279", "C4298", "C4299", "C4301", "C4303", "C4314", "C4315", "C4317", "C4318", "C4321", "C4322", "C4323", "C4327", "C4328", "C4330", "C4338", "C4352", "C4362", "C4367", "C4370", "C4380", "C4387", "C4388"]
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ms.assetid: 170248db-7bf2-4823-92d9-437b04c1290d
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description: "Table of Microsoft C/C++ compiler warnings C4200 through C4389."
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ms.date: 10/18/2020
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f1_keywords: ["C4203", "C4277", "C4279", "C4298", "C4299", "C4301", "C4303", "C4314", "C4315", "C4317", "C4318", "C4321", "C4322", "C4323", "C4327", "C4328", "C4330", "C4338", "C4352", "C4362", "C4367", "C4370", "C4380", "C4387"]
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---
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# Compiler warnings C4200 Through C4399
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# Compiler warnings C4200 through C4399
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The articles in this section of the documentation explain a subset of the warning messages that are generated by the compiler.
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|[Compiler warning (level 1) C4383](../../error-messages/compiler-warnings/compiler-warning-level-1-c4383.md)|'*instance_dereference_operator*': the meaning of dereferencing a handle can change, when a user-defined '*instance_dereference_operator*' operator exists; write the operator as a static function to be explicit about the operand|
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|[Compiler warning (level 1) C4384](../../error-messages/compiler-warnings/compiler-warning-level-1-c4384.md)|#pragma 'make_public' should only be used at global scope|
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|Compiler warning (level 3) C4387|'*alternative*': was considered|
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|Compiler warning (level 4) C4388|'*expression*': signed/unsigned mismatch|
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|[Compiler warning (level 4) C4388](./c4388.md))|'*expression*': signed/unsigned mismatch|
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|[Compiler warning (level 4) C4389](../../error-messages/compiler-warnings/compiler-warning-level-4-c4389.md)|'*operator*': signed/unsigned mismatch|
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|[Compiler warning (level 3) C4390](../../error-messages/compiler-warnings/compiler-warning-level-3-c4390.md)|';': empty controlled statement found; is this the intent?|
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|[Compiler warning (level 1) C4391](../../error-messages/compiler-warnings/compiler-warning-level-1-c4391.md)|'*function_signature*': incorrect return type for intrinsic function, expected '*type*'|

‎docs/error-messages/compiler-warnings/compiler-warnings-c4800-through-c4999.md

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---
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title: "Compiler warnings C4800 Through C5999"
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ms.date: "04/21/2019"
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description: "Table of Microsoft C/C++ compiler warnings C4800 through C5999."
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ms.date: 10/18/2020
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f1_keywords: ["C4808", "C4809", "C4825", "C4827", "C4837", "C4841", "C4842", "C4843", "C4844", "C4845", "C4846", "C4847", "C4848", "C4854", "C4855", "C4856", "C4857", "C4872", "C4880", "C4881", "C4882", "C4916", "C4921", "C4934", "C4954", "C4955", "C4963", "C4966", "C4970", "C4971", "C4973", "C4974", "C4981", "C4987", "C4988", "C4989", "C4990", "C4991", "C4992", "C4998", "C5022", "C5023", "C5024", "C5025", "C5026", "C5027", "C5028", "C5029", "C5030", "C5031", "C5032", "C5033", "C5034", "C5035", "C5036", "C5037", "C5039", "C5040", "C5041", "C5042", "C5043", "C5044", "C5047", "C5048", "C5049", "C5050", "C5051", "C5052", "C5053", "C5054", "C5055", "C5056", "C5057", "C5058", "C5059", "C5060", "C5061", "C5062", "C5063", "C5100", "C5101", "C5102", "C5103", "C5104", "C5106", "C5107", "C5108", "C5200", "C5201", "C5202", "C5203", "C5204", "C5205", "C5206", "C5207"]
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helpviewer_keywords: ["C4808", "C4809", "C4825", "C4827", "C4837", "C4841", "C4842", "C4843", "C4844", "C4845", "C4846", "C4847", "C4848", "C4854", "C4855", "C4856", "C4857", "C4872", "C4880", "C4881", "C4882", "C4916", "C4921", "C4934", "C4954", "C4955", "C4963", "C4966", "C4970", "C4971", "C4973", "C4974", "C4981", "C4987", "C4988", "C4989", "C4990", "C4991", "C4992", "C4998", "C5022", "C5023", "C5024", "C5025", "C5026", "C5027", "C5028", "C5029", "C5030", "C5031", "C5032", "C5033", "C5034", "C5035", "C5036", "C5037", "C5039", "C5040", "C5041", "C5042", "C5043", "C5044", "C5047", "C5048", "C5049", "C5050", "C5051", "C5052", "C5053", "C5054", "C5055", "C5056", "C5057", "C5058", "C5059", "C5060", "C5061", "C5062", "C5063", "C5100", "C5101", "C5102", "C5103", "C5104", "C5106", "C5107", "C5108", "C5200", "C5201", "C5202", "C5203", "C5204", "C5205", "C5206", "C5207"]
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helpviewer_keywords: ["C4808", "C4809", "C4825", "C4827", "C4837", "C4841", "C4842", "C4843", "C4844", "C4845", "C4846", "C4847", "C4848", "C4854", "C4855", "C4856", "C4857", "C4872", "C4880", "C4881", "C4882", "C4916", "C4921", "C4934", "C4954", "C4955", "C4963", "C4966", "C4970", "C4971", "C4973", "C4974", "C4981", "C4987", "C4988", "C4989", "C4990", "C4991", "C4992", "C4998", "C5022", "C5023", "C5024", "C5025", "C5026", "C5027", "C5028", "C5029", "C5030", "C5031", "C5032", "C5033", "C5034", "C5035", "C5036", "C5037", "C5039", "C5040", "C5041", "C5042", "C5043", "C5044", "C5047", "C5048", "C5049", "C5050", "C5051", "C5052", "C5053", "C5054", "C5055", "C5056", "C5057", "C5058", "C5059", "C5060", "C5061", "C5062", "C5063", "C5100", "C5101", "C5102", "C5103", "C5104", "C5106", "C5107", "C5108", "C5200", "C5201", "C5202", "C5203", "C5204", "C5205", "C5206", "C5207", "C5209", "C5210", "C5211", "C5212", "C5213", "C5214", "C5215", "C5216", "C5217", "C5218", "C5219", "C5220", "C5221"]
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---
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# Compiler warnings C4800 Through C5999
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# Compiler warnings C4800 through C5999
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The articles in this section of the documentation explain a subset of the warning messages that are generated by the compiler.
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| Compiler warning C5206 | deduced return types for coroutines is a non-standard extension |
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| Compiler warning C5207 | the simple requirement asserts the validity of expression '`e->id`'. Did you mean '`{ e } -> id`'? You can suppress the warning using '`{ e->id }`' |
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| [Compiler warning (level 1) C5208](c5208.md) | unnamed class used in `typedef` name cannot declare members other than non-static data members, member enumerations, or member classes |
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| Compiler warning C5209 | the C++20 syntax for an init-capture has changed to '& ...opt identifier initializer' |
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| Compiler warning C5210 | '*name*' is not a valid header unit reference; ignoring |
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| Compiler warning C5212 | '*name*' is not a valid named reference; treating as reference to file |
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| Compiler warning C5213 | '*name*' named reference is treated as a named partition but the name is not specified; treating as reference to file |
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| Compiler warning C5214 | applying '*modifier*' to an operand with a volatile qualified type is deprecated in C++20 |
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| Compiler warning C5215 | '*name*' a function parameter with a volatile qualified type is deprecated in C++20 |
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| Compiler warning C5216 | '*name*' a volatile qualified return type is deprecated in C++20 |
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| Compiler warning C5217 | a structured binding declaration that includes volatile is deprecated in C++20 |
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| Compiler warning C5218 | destroying delete may not behave as intended when non-conforming switches '`/Zc:sizedDealloc-`' or '`/Zc:alignedNew-`' are used |
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| Compiler warning C5219 | implicit conversion from '*type-1*' to '*type-2*', possible loss of data |
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| Compiler warning C5220 | '*name*': a non-static data member with a volatile qualified type no longer implies that compiler generated copy/move constructors and copy/move assignment operators are not trivial |
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| Compiler warning C5221 | `xfg::rename` is deprecated. |
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## See also
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‎docs/error-messages/toc.yml

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href: compiler-warnings/compiler-warning-level-1-c4383.md
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- name: Compiler warning (level 1) C4384
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href: compiler-warnings/compiler-warning-level-1-c4384.md
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- name: Compiler warning (level 4) C4388
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href: compiler-warnings/c4388.md
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- name: Compiler warning (level 4) C4389
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href: compiler-warnings/compiler-warning-level-4-c4389.md
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- name: Compiler warning (level 3) C4390

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