Compiler Error C2178

'identifier' cannot be declared with 'specifier' specifier

Remarks

A mutable specifier was used in a declaration, but the specifier is not allowed in this context. It can only be applied to non-static, non-const, and non-reference data members. For more information, see Mutable Data Members.

A consteval specifier was used on a destructor, allocation function, or deallocation function.

Example: mutable

The following example shows how C2178 may occur with the mutable specifier, and how to resolve it:

// C2178_mutable.cpp
// compile with: /c

struct S
{
    mutable const int i;   // C2178, remove mutable or const to resolve
};

mutable int x = 4;   // C2178, remove mutable to resolve

Example: consteval

The following example shows how C2178 may occur with the consteval specifier. To resolve this error, remove all consteval specifiers:

// C2178_consteval.cpp
// compile with: /c /std:c++20

#include <cstddef>

struct S
{
    consteval ~S() {}   // C2178

    consteval static void* operator new(std::size_t size);   // C2178
    consteval static void operator delete(void* ptr);        // C2178
};