Page History

...

The identifiers and attribute names mentioned above are :  override, final, alignas, carries_dependency, deprecated, and noreturn.

...

Noncompliant Code Example (Header Guard)

A common , but noncompliant , practice is to choose a reserved name for a macro used in a preprocessor conditional guarding against multiple inclusions of a header file (see also PRE06-C. Enclose header files in an inclusion guard). The name may clash with reserved names defined by the implementation of the C++ standard template library in its headers or with reserved names implicitly predefined by the compiler even when no C++ standard library header is included.

...

#ifndef MY_HEADER_H
#define MY_HEADER_H

// Contents of <my_header.h>

#endif // MY_HEADER_H

Noncompliant Code Example (User-

...

Defined Literal)

In this noncompliant code example, a user-defined literal operator"" x is declared. However, literal suffix identifiers are required to start with an underscore; literal suffixes without the underscore prefix are reserved for future library implementations:

#include <cstddef>
 
unsigned int operator"" x(const char *, std::size_t);

Compliant Solution (User-

...

Defined Literal)

In this compliant solution, the user-defined literal is named operator"" _x, which is not a reserved identifier:

...

In this noncompliant code example, the names of the file scope objects _max_limit and _limit both begin with an underscore. Since Because it is static, the declaration of _max_limit might seem to be impervious to clashes with names defined by the implementation. However, because the header <cstddef> is included to define std::size_t, a potential for a name clash exists. (Note, however, that a conforming compiler may implicitly declare reserved names regardless of whether or not any C++ standard template library header has been explicitly included.) In addition, because _limit has external linkage, it may clash with a symbol with the same name defined in the language runtime library even if such a symbol is not declared in any header. Consequently, it is unsafe to start the name of any file scope identifier with an underscore , even if its linkage limits its visibility to a single translation unit.

...

In this noncompliant code example, because the C++ standard template library header <cinttypes> is specified to include <cstdint>, as per [c.files] paragraph 4, the name MAX_SIZE conflicts with the name of the <cstdint> header macro used to denote the upper limit of std:size_t:

#include <cinttypes> // for int_fast16_t

void f(std::int_fast16_t val) {
  enum { MAX_SIZE = 80 };
  // ...
}

...

DCL32-CPP-EX2: As a compiler vendor or standard library developer, it is acceptable to use identifiers reserved for your implementation. Reserved identifiers may be defined by the compiler, in standard library headers, or in headers included by a standard library header, as in this example declaration from the libc++ STL implementation:

...