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Merge pull request #5159 from TylerMSFT/warning
add new warning for VS 17.6 - C5266
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‎docs/error-messages/compiler-warnings/c4834.md

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---
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description: "Learn about the cause and fixes for Compiler warning (level 1) C4834."
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title: "Compiler warning (Level 1) C4834"
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ms.date: 07/26/2021
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ms.date: 01/18/2024
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f1_keywords: ["C4834"]
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helpviewer_keywords: ["C4834"]
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## Remarks
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Starting in the C++17 Standard, the `[[nodiscard]]` attribute specifies that a function's return value isn't intended to be discarded. If a caller discards the return value, the compiler generates warning C4834.
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Starting in the C++17 Standard, the `[[nodiscard]]` attribute specifies that a function's return value isn't intended to be discarded. If a caller discards the return value, the compiler generates warning C4834. Although this attribute was introduced in C++17, the compiler respects this attribute and generates warnings related to it when using `/std:c++14` and later.
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To resolve this warning, consider why your code doesn't use the return value. Your use of the function may not match its intent. You can circumvent the warning by assigning the value to **`std::ignore`** or by casting it to **`void`** if discarding the value is intentional.
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Assignment to **`std::ignore`** is preferred over casting to **`void`** in C++11 and higher, as it makes your intent clearer and will not trigger [Warning C26457](../../code-quality/c26457.md) if enabled in your code analysis settings.

‎docs/error-messages/compiler-warnings/compiler-warning-level-4-c5266.md

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---
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description: "Learn more about: Compiler Warning (level 4) C5266"
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title: "Compiler Warning (level 4) C5266"
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ms.date: 01/18/2024
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f1_keywords: ["C5266"]
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helpviewer_keywords: ["C5266"]
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---
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# Compiler Warning (level 4) C5266
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> 'const' qualifier on return type has no effect
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The C++ Standard specifies that a top-level const (or volatile) qualification on a function return type is ignored.
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This warning is off by default.\
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This warning was introduced in Visual Studio 17.6
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## Example
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The following sample generates C5266:
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```cpp
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// compile with: /W4 /c
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#pragma warning(default : 5266) // enable warning C5266 because it's off by default (or compile with /w45266)
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const int f() // warning C5266: 'const' qualifier on return type has no effect
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{
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return 13;
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}
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```
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## See also
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[Enable warnings that are off by default](../../preprocessor/compiler-warnings-that-are-off-by-default.md)

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

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title: "Compiler Warnings by compiler version"
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description: "Table of Microsoft C/C++ compiler warnings by compiler version."
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ms.date: 02/28/2023
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ms.date: 01/18/2024
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helpviewer_keywords: ["warnings, by compiler version", "cl.exe compiler, setting warning options"]
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# Compiler Warnings by compiler version
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| Visual Studio 2022 version 17.3 | 19.33 |
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| Visual Studio 2022 version 17.4 | 19.34 |
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| Visual Studio 2022 version 17.5 | 19.35 |
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| Visual Studio 2022 version 17.6 | 19.36 |
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| Visual Studio 2022 version 17.7 | 19.37 |
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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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|--|--|
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| C5267 | definition of implicit copy constructor/assignment operator for '*type*' is deprecated because it has a user-provided assignment operator/copy constructor |
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## Warnings introduced in Visual Studio 2022 version 17.6 (compiler version 19.36)
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These warnings, and all warnings in later versions, are suppressed by using the compiler option **`/Wv:19.35`**.
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| Warning | Message |
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|--|--|
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| [C5266](compiler-warning-level-4-c5266.md) | 'const' qualifier on return type has no effect |
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## Warnings introduced in Visual Studio 2022 version 17.5 (compiler version 19.35)
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These warnings, and all warnings in later versions, are suppressed by using the compiler option **`/Wv:19.34`**.

‎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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description: "Table of Microsoft C/C++ compiler warnings C4800 through C5999."
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ms.date: 03/01/2023
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f1_keywords: ["C4808", "C4809", "C4825", "C4827", "C4837", "C4842", "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", "C4983", "C4987", "C4988", "C4989", "C4990", "C4991", "C4992", "C4998", "C5022", "C5023", "C5024", "C5025", "C5026", "C5027", "C5028", "C5029", "C5030", "C5031", "C5032", "C5034", "C5035", "C5036", "C5039", "C5040", "C5041", "C5042", "C5043", "C5044", "C5047", "C5048", "C5049", "C5051", "C5052", "C5053", "C5057", "C5058", "C5059", "C5060", "C5061", "C5062", "C5063", "C5081", "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", "C5222", "C5223", "C5224", "C5225", "C5226", "C5227", "C5228", "C5229", "C5230", "C5231", "C5232", "C5233", "C5234", "C5235", "C5236", "C5237", "C5238", "C5239", "C5241", "C5242", "C5244", "C5245", "C5246", "C5249", "C5250", "C5251", "C5252", "C5253", "C5254", "C5255", "C5256", "C5257", "C5258", "C5259", "C5260", "C5261", "C5263", "C5264", "C5300"]
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helpviewer_keywords: ["C4808", "C4809", "C4825", "C4827", "C4837", "C4842", "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", "C4983", "C4987", "C4988", "C4989", "C4990", "C4991", "C4992", "C4998", "C5022", "C5023", "C5024", "C5025", "C5026", "C5027", "C5028", "C5029", "C5030", "C5031", "C5032", "C5034", "C5035", "C5036", "C5039", "C5040", "C5041", "C5042", "C5043", "C5044", "C5047", "C5048", "C5049", "C5051", "C5052", "C5053", "C5057", "C5058", "C5059", "C5060", "C5061", "C5062", "C5063", "C5081", "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", "C5222", "C5223", "C5224", "C5225", "C5226", "C5227", "C5228", "C5229", "C5230", "C5231", "C5232", "C5233", "C5234", "C5235", "C5236", "C5237", "C5238", "C5239", "C5241", "C5242", "C5244", "C5245", "C5246", "C5249", "C5250", "C5251", "C5252", "C5253", "C5254", "C5255", "C5256", "C5257", "C5258", "C5259", "C5260", "C5261", "C5263", "C5264", "C5300"]
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ms.date: 01/18/2024
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f1_keywords: ["C4808", "C4809", "C4825", "C4827", "C4837", "C4842", "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", "C4983", "C4987", "C4988", "C4989", "C4990", "C4991", "C4992", "C4998", "C5022", "C5023", "C5024", "C5025", "C5026", "C5027", "C5028", "C5029", "C5030", "C5031", "C5032", "C5034", "C5035", "C5036", "C5039", "C5040", "C5041", "C5042", "C5043", "C5044", "C5047", "C5048", "C5049", "C5051", "C5052", "C5053", "C5057", "C5058", "C5059", "C5060", "C5061", "C5062", "C5063", "C5081", "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", "C5222", "C5223", "C5224", "C5225", "C5226", "C5227", "C5228", "C5229", "C5230", "C5231", "C5232", "C5233", "C5234", "C5235", "C5236", "C5237", "C5238", "C5239", "C5241", "C5242", "C5244", "C5245", "C5246", "C5249", "C5250", "C5251", "C5252", "C5253", "C5254", "C5255", "C5256", "C5257", "C5258", "C5259", "C5260", "C5261", "C5263", "C5264", "C5266", "C5300"]
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helpviewer_keywords: ["C4808", "C4809", "C4825", "C4827", "C4837", "C4842", "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", "C4983", "C4987", "C4988", "C4989", "C4990", "C4991", "C4992", "C4998", "C5022", "C5023", "C5024", "C5025", "C5026", "C5027", "C5028", "C5029", "C5030", "C5031", "C5032", "C5034", "C5035", "C5036", "C5039", "C5040", "C5041", "C5042", "C5043", "C5044", "C5047", "C5048", "C5049", "C5051", "C5052", "C5053", "C5057", "C5058", "C5059", "C5060", "C5061", "C5062", "C5063", "C5081", "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", "C5222", "C5223", "C5224", "C5225", "C5226", "C5227", "C5228", "C5229", "C5230", "C5231", "C5232", "C5233", "C5234", "C5235", "C5236", "C5237", "C5238", "C5239", "C5241", "C5242", "C5244", "C5245", "C5246", "C5249", "C5250", "C5251", "C5252", "C5253", "C5254", "C5255", "C5256", "C5257", "C5258", "C5259", "C5260", "C5261", "C5263", "C5264", "C5266", "C5300"]
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# Compiler warnings C4800 through C5999
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| [Compiler warning (level 1, error, off) C5262](c5262.md) | implicit fall-through occurs here; are you missing a break statement? Use `[[fallthrough]]` when a `break` statement is intentionally omitted between cases |
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| Compiler warning (level 4, off) C5263 | calling '`std::move`' on a temporary object prevents copy elision |
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| Compiler warning (level 4, off) C5264 | '*variable-name*': 'const' variable is not used |
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| [Compiler warning (level 4, off) C5266](compiler-warning-level-4-c5266.md) | 'const' qualifier on return type has no effect |
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| [Compiler warning C5267](c5267.md) | definition of implicit copy constructor/assignment operator for '*type*' is deprecated because it has a user-provided assignment operator/copy constructor |
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| Compiler warning (level 1, error) C5300 | '#pragma omp atomic': left operand of '*operator*' must match left hand side of assignment-expression |
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| [Compiler warning (level 1) C5301](c5301-c5302.md) | '#pragma omp for': '*loop-index*' increases while loop condition uses '*comparison*'; non-terminating loop? |

‎docs/error-messages/toc.yml

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href: compiler-warnings/c5248.md
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- name: Compiler warning (level 1, error, off) C5262
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href: compiler-warnings/c5262.md
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- name: Compiler warning (level 4) C5266
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- name: Compiler warning (level 4) C5267
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- name: Compiler warning (level 1) C5301 and C5302

‎docs/preprocessor/compiler-warnings-that-are-off-by-default.md

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description: "Learn more about: Compiler warnings that are off by default"
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title: "Compiler warnings that are off by default"
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ms.date: 01/18/2024
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helpviewer_keywords: ["warnings, compiler", "cl.exe compiler, setting options"]
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# Compiler warnings that are off by default
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| [C5262](../error-messages/compiler-warnings/c5262.md) (level 1, error) | implicit fall-through occurs here; are you missing a `break` statement? Use `[[fallthrough]]` when a `break` statement is intentionally omitted between cases <sup>17.4</sup> |
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| C5263 (level 4) | calling '`std::move`' on a temporary object prevents copy elision <sup>17.4</sup> |
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| C5264 (level 4) | '*variable-name*': 'const' variable is not used <sup>17.4</sup> |
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| [C5266 (level 4)](../error-messages/compiler-warnings/compiler-warning-level-4-c5266.md) | 'const' qualifier on return type has no effect <sup>17.6</sup> |
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| [C5267](../error-messages/compiler-warnings/c5267.md) (level 4) | definition of implicit copy constructor/assignment operator for '*type*' is deprecated because it has a user-provided assignment operator/copy constructor <sup>17.7</sup> |
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<sup>14.1</sup> This warning is available starting in Visual Studio 2015 Update 1.\

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