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First batch of doc updates for CppCoreCheck
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‎docs/code-quality/c26441.md‎

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---
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description: "Learn more about: Warning C26441 NO_UNNAMED_GUARDS"
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title: Warning C26441
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ms.date: 2/7/2023
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description: "Learn more about: Warning C26441 NO_UNNAMED_GUARDS"
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ms.date: 5/11/2023
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f1_keywords: ["C26441", "NO_UNNAMED_GUARDS"]
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helpviewer_keywords: ["C26441"]
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---
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This diagnostic only analyzes the standard lock types `std::scoped_lock`, `std::unique_lock`, and `std::lock_guard`. Warning [C26444](c26444.md) covers other unnamed RAII types.
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The analyzer only analyzes simple calls to constructors. More complex initializer expressions may lead to inaccurate results in the form of missed warnings. Locks passed as arguments to function calls or returned as results of function calls are ignored because the analysis tool is unable to determine if those locks are deliberately trying to protect that function call or if they should be extended. To provide similar protection for types returned by a function call, annotate them with `[[nodiscard]]`. The analyzer ignores locks created as temporaries but assigned to named references to extend their lifetime.
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The analyzer only analyzes simple calls to constructors. More complex initializer expressions may lead to inaccurate results in the form of missed warnings. Locks passed as arguments to function calls or returned as results of function calls are ignored because the analysis tool is unable to determine if those locks are deliberately trying to protect that function call or if they should be extended. To provide similar protection for types returned by a function call, annotate them with `[[nodiscard]]`. You can also annotate constructors with `[[nodiscard]]` to avoid unnamed objects of that type. The analyzer ignores locks created as temporaries but assigned to named references to extend their lifetime.
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Code analysis name: `NO_UNNAMED_GUARDS`
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‎docs/code-quality/c26444.md‎

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---
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description: "Learn more about: Warning C26444 NO_UNNAMED_RAII_OBJECTS"
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title: Warning C26444
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ms.date: 01/18/2017
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description: "Learn more about: Warning C26444 NO_UNNAMED_RAII_OBJECTS"
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ms.date: 05/11/2023
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f1_keywords: ["C26444", "NO_UNNAMED_RAII_OBJECTS"]
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helpviewer_keywords: ["C26444"]
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---
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# Warning C26444
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> Avoid unnamed objects with custom construction and destruction.
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> Don't try to declare a local variable with no name (es.84).
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## C++ Core Guidelines
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[ES.84: Don't (try to) declare a local variable with no name](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-noname)
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[ES.84: Don't (try to) declare a local variable with no name](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-noname)
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Unnamed (that is, temporary) objects with non-trivial behavior may point to either (a) inefficient code that allocates and immediately throws away resources or (b) to the code that unintentionally ignores non-primitive data. Sometimes it may also indicate plainly wrong declaration.
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## Notes
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## Remarks
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- This rule detects types with non-deleted destructors. Keep in mind that destructors can be compiler generated.
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- The warning can flag code that isn't compiler generated and that invokes either a non-default constructor of a RAII type or a function that returns an object of such type. This warning helps to detect ignored call results in addition to wrong declarations.
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- This rule detects types with non-trivial destructors. Keep in mind that destructors can be compiler generated.
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- The warning can flag code that invokes either a non-trivial constructor of a RAII type.
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- The logic skips temporaries if they're used in higher-level expressions. One example is temporaries that are passed as arguments or used to invoke a function.
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- The standard library implementation may have different versions of destruction logic for some types (for example, containers). This can produce noisy warnings on debug builds because it's customary to ignore iterators returned from calls like [`std::vector::insert`](../standard-library/vector-class.md#insert). While such warnings aren't actionable in most cases, they're legitimate in pointing to the place where some non-obvious work is done in temporary objects.
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Code analysis name: `NO_UNNAMED_RAII_OBJECTS`
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## Example: Ignored call result
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## Examples
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```cpp
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std::string ToTraceMessage(State &state);
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void SaveState(State &state)
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struct A { A(int i); ~A(); };
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void Foo()
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{
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// ...
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ToTraceMessage(state); // C26444, should we do something with the result of this call?
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A{42}; // warning C26444: Don't try to declare a local variable with no name (es.84).
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}
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```
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Example: Ignored call result - fixed.
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std::cerr << ToTraceMessage(state);
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To fix the issue, convert the temporary object to a local.
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Example: Unexpected lifetime.
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void SplitCache()
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```cpp
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struct A { A(int i); ~A(); };
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void Foo()
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{
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gsl::finally([] { RestoreCache(); }); // C26444, RestoreCache is invoked immediately!
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//...
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A guard{42}; // OK.
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}
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Example: Unexpected lifetime - fixed.
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const auto _ = gsl::finally([] { RestoreCache(); });
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```
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## See also
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[ES.84: Don't (try to) declare a local variable with no name](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md)
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[C26441](C26441.md)\
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[ES.84: Don't (try to) declare a local variable with no name](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-noname)

‎docs/code-quality/c26449.md‎

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---
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description: "Learn more about: Warning C26449 NO_SPAN_FROM_TEMPORARY"
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title: Warning C26449
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ms.date: 03/22/2018
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description: "Learn more about: Warning C26449 NO_SPAN_FROM_TEMPORARY"
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ms.date: 05/11/2024
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f1_keywords: ["C26449", "NO_SPAN_FROM_TEMPORARY"]
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helpviewer_keywords: ["C26449"]
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---
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# Warning C26449
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> `gsl::span` or `std::string_view` created from a temporary will be invalid when the temporary is invalidated (gsl.view)
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C++ Core Guidelines: [GSL.view: Views](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gslview-views).
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C++ Core Guidelines: [GSL.view: Views](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#SS-views).
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Spans and views are convenient and lightweight types that allow you to reference memory buffers. But they must be used carefully: while their interface looks similar to standard containers, their behavior is more like the behavior of pointers and references. They don't own data and must never be constructed from temporary buffers. This check focuses on cases where source data is temporary, while a span or view isn't. This rule can help to avoid subtle but dangerous mistakes made when legacy code gets modernized and adopts spans or views. There's another check that handles a slightly different scenario involving span references: [C26445 NO_SPAN_REF](c26445.md).
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Spans and views are convenient and lightweight types that allow you to reference memory buffers. But they must be used carefully: while their interface looks similar to standard containers, their behavior is more like the behavior of pointers and references. They don't own data and must never be constructed from temporary buffers. This check focuses on cases where source data is temporary, while a span or view isn't. There's another check that handles a slightly different scenario involving span references: [C26445 NO_SPAN_REF](c26445.md). Both rules can help to avoid subtle but dangerous mistakes made when legacy code gets modernized and adopts spans or views.
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Consider using [C26815](c26815.md) and [C26816](c26816.md). Those are more general versions of this check.
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## Remarks
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gsl::span<const sequence_item> get_seed_sequence() noexcept;
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// Returns a generated collection. Doesn't own new data.
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const std::vector<sequence_item> get_next_sequence(gsl::span<const sequence_item>);
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std::vector<sequence_item> get_next_sequence(gsl::span<const sequence_item>);
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void run_batch()
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{
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}
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}
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```
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To fix the issue, make sure the view is created from an object that lives at least as long as the view itself. Sometimes this can be achieved by copying the data, other times some APIs need to be redesigned.
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## See also
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[C26815](c26815.md)\
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[C26816](c26816.md)

‎docs/code-quality/c26450.md‎

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---
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description: "Learn more about: Arithmetic overflow: '%operator%' operation causes overflow at compile time. Use a wider type to store the operands"
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title: Warning C26450
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ms.date: 01/08/2017
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description: "Describes the causes of MSVC code analysis warning C26450 and how to fix it"
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ms.date: 05/11/2023
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f1_keywords: ["C26450", "RESULT_OF_ARITHMETIC_OPERATION_PROVABLY_LOSSY"]
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helpviewer_keywords: ["C26450"]
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---
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# Warning C26450
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>Arithmetic overflow: '*operator*' operation causes overflow at compile time. Use a wider type to store the operands (io.1)
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> Arithmetic overflow: '*operator*' operation causes overflow at compile time. Use a wider type to store the operands (io.1)
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## Remarks
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This warning indicates that an arithmetic operation was provably lossy at compile time. It can be asserted when the operands are all compile-time constants. Currently, we check left shift, multiplication, addition, and subtraction operations for such overflows.
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Warning C4307 is a similar check in the Microsoft C++ compiler.
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Warning [C4307](https://learn.microsoft.com/cpp/error-messages/compiler-warnings/compiler-warning-level-2-c4307) is a similar check in the Microsoft C++ compiler.
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Code analysis name: `RESULT_OF_ARITHMETIC_OPERATION_PROVABLY_LOSSY`
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## Example 1
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## Examples
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```cpp
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int multiply()
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{
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const int a = INT_MAX;
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const int b = 2;
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long long c = (long long)a * b; // OK
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return c;
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}
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```
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## Example 2
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```cpp
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int add()
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{
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const int a = INT_MAX;
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const int b = 2;
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int c = a + b; // C26450 reported here
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return c;
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}
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```
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To correct this warning, use the following code:
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```cpp
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long long add()
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{
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const int a = INT_MAX;
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const int b = 2;
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long long c = (long long)a + b; // OK
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return c;
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}
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```
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## Example 3
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```cpp
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int subtract()
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{
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const int a = -INT_MAX;
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const int b = 2;
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int c = a - b; // C26450 reported here
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return c;
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}
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```
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To correct this warning, use the following code.
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```cpp
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long long subtract()
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{
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const int a = -INT_MAX;
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const int b = 2;
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long long c = (long long)a - b; // OK
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long long c = static_cast<long long>(a) * b; // OK
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return c;
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}
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```
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## See also
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[ES.103: Don't overflow](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-overflow)
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[26451](c26451.md)\
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[26452](c26452.md)\
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[26453](c26453.md)\
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[26454](c26454.md)\
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[ES.103: Don't overflow](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-overflow)

‎docs/code-quality/c26451.md‎

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---
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title: Warning C26451
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description: "Describes the causes of MSVC code analysis warning C26451, and shows how to fix it."
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ms.date: 07/15/2020
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ms.date: 05/11/2023
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f1_keywords: ["C26451", "RESULT_OF_ARITHMETIC_OPERATION_CAST_TO_LARGER_SIZE"]
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helpviewer_keywords: ["C26451"]
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Code analysis name: `RESULT_OF_ARITHMETIC_OPERATION_CAST_TO_LARGER_SIZE`
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## Example 1
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## Examples
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The following code generates this warning:
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```cpp
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void leftshift(int i) noexcept
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{
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unsigned __int64 x;
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unsigned long long x;
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x = i << 31; // C26451 reported here
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// code
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```cpp
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void leftshift(int i) noexcept
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{
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unsigned __int64 x;
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x = static_cast<unsigned __int64>(i) << 31; // OK
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unsigned long long x;
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x = static_cast<unsigned long long>(i) << 31; // OK
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// code
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}
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```
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## Example 2
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```cpp
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void somefunc(__int64 /* y */) noexcept
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{}
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void callsomefunc(int x) noexcept
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{
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somefunc(x * 2); // C26451 reported here
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}
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```
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To correct this warning, use the following code:
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```cpp
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void callsomefunc(int x) noexcept
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{
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somefunc(static_cast<__int64>(x) * 2); // OK
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}
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```
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## Example 3
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```cpp
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__int64 add(int x) noexcept
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{
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constexpr auto value = 2;
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return x += value; // C26451 reported here
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}
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```
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```cpp
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__int64 add(int x) noexcept
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{
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constexpr auto value = 2;
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const __int64 y = static_cast<__int64>(x) + value; // OK
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return y;
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}
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```
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## See also
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- [ES.103: Don't overflow](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-overflow)
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[26450](c26450.md)\
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[26452](c26452.md)\
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[26453](c26453.md)\
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[26454](c26454.md)\
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[ES.103: Don't overflow](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-overflow)

‎docs/code-quality/c26452.md‎

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This warning indicates the shift count is negative, or greater than or equal to the number of bits in the shifted operand. Either case results in undefined behavior.
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Warning C4293 is a similar check in the Microsoft C++ compiler.
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Warning [C4293](https://learn.microsoft.com/cpp/error-messages/compiler-warnings/compiler-warning-level-1-c4293) is a similar check in the Microsoft C++ compiler.
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Code analysis name: `SHIFT_COUNT_NEGATIVE_OR_TOO_BIG`
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## Example
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```cpp
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unsigned __int64 combine(unsigned lo, unsigned hi)
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unsigned long long combine(unsigned lo, unsigned hi)
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To correct this warning, use the following code:
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```cpp
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unsigned __int64 combine(unsigned lo, unsigned hi)
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unsigned long long combine(unsigned lo, unsigned hi)
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{
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}
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```
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## See also
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[ES.102: Use signed types for arithmetic](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-unsigned)
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[26450](c26450.md)\
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[26451](c26451.md)\
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[26453](c26453.md)\
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[26454](c26454.md)\
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[ES.101: Use unsigned types for bit manipulation](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-unsigned)\
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[ES.102: Use signed types for arithmetic](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-signed)

‎docs/code-quality/c26453.md‎

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---
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title: Warning C26453
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description: "Describes the causes of MSVC code analysis warning C26453, and shows how to fix it."
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ms.date: 07/15/2020
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ms.date: 05/11/2023
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f1_keywords: ["C26453", "LEFTSHIFT_NEGATIVE_SIGNED_NUMBER"]
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helpviewer_keywords: ["C26453"]
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```cpp
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void leftshift(int shiftCount)
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{
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const auto result = ~0u << shiftCount; // OK
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// code
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}
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```
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## See also
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[ES.102: Use signed types for arithmetic](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-unsigned)
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[26450](c26450.md)\
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[26451](c26451.md)\
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[26452](c26452.md)\
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[26454](c26454.md)\
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[ES.101: Use unsigned types for bit manipulation](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-unsigned)\
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[ES.102: Use signed types for arithmetic](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-signed)

‎docs/code-quality/c26454.md‎

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## See also
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[ES.106: Don't try to avoid negative values by using unsigned](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-nonnegative)
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[26450](c26450.md)\
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[26451](c26451.md)\
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[26452](c26452.md)\
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[26453](c26453.md)\
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[ES.106: Don't try to avoid negative values by using unsigned](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-nonnegative)

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