17 Library introduction [library]

17.6 Library-wide requirements [requirements]

17.6.4 Constraints on programs [constraints]

17.6.4.3 Reserved names [reserved.names]

1

The C++ standard library reserves the following kinds of names:

2

If a program declares or defines a name in a context where it is reserved, other than as explicitly allowed by this Clause, its behavior is undefined.

17.6.4.3.1 Macro names [macro.names]

1

A translation unit that includes a standard library header shall not #define or #undef names declared in any standard library header.

2

A translation unit shall not #define or #undef names lexically identical to keywords, to the identifiers listed in Table [tab:identifiers.special], or to the attribute-tokens described in [dcl.attr].

17.6.4.3.2 Global names [global.names]

1

Certain sets of names and function signatures are always reserved to the implementation:

  • (1.1)

    Each name that contains a double underscore __ or begins with an underscore followed by an uppercase letter ([lex.key]) is reserved to the implementation for any use.

  • (1.2)

    Each name that begins with an underscore is reserved to the implementation for use as a name in the global namespace.

17.6.4.3.3 External linkage [extern.names]

1

Each name declared as an object with external linkage in a header is reserved to the implementation to designate that library object with external linkage,183 both in namespace std and in the global namespace.

2

Each global function signature declared with external linkage in a header is reserved to the implementation to designate that function signature with external linkage. 184

3

Each name from the Standard C library declared with external linkage is reserved to the implementation for use as a name with extern "C" linkage, both in namespace std and in the global namespace.

4

Each function signature from the Standard C library declared with external linkage is reserved to the implementation for use as a function signature with both extern "C" and extern "C++" linkage, 185 or as a name of namespace scope in the global namespace.

182)

The list of such reserved names includes errno, declared or defined in <cerrno>.

183)

The list of such reserved function signatures with external linkage includes setjmp(jmp_buf), declared or defined in <csetjmp>, and va_end(va_list), declared or defined in <cstdarg>.

184)

The function signatures declared in <cuchar>, <cwchar>, and <cwctype> are always reserved, notwithstanding the restrictions imposed in subclause 4.5.1 of Amendment 1 to the C Standard for these headers.

17.6.4.3.4 Types [extern.types]

1

For each type T from the Standard C library,186 the types ::T and std::T are reserved to the implementation and, when defined, ::T shall be identical to std::T.

185)

These types are clock_t, div_t, FILE, fpos_t, lconv, ldiv_t, mbstate_t, ptrdiff_t, sig_atomic_t, size_t, time_t, tm, va_list, wctrans_t, wctype_t, and wint_t.

17.6.4.3.5 User-defined literal suffixes [usrlit.suffix]

1

Literal suffix identifiers that do not start with an underscore are reserved for future standardization.