[cpp.predefined]

The following macro names shall be defined by the implementation:

(1.1)
__cplusplus

The integer literal 202002L.

[ Note
:
It is intended that future versions of this International Standard will replace the value of this macro with a greater value.
— end note
]
(1.2)
__DATE__

The date of translation of the source file: a character string literal of the form "Mmm dd yyyy", where the names of the months are the same as those generated by the asctime function, and the first character of dd is a space character if the value is less than 10.

If the date of translation is not available, an implementation-defined valid date shall be supplied.
(1.3)
__FILE__

The presumed name of the current source file (a character string literal).149
(1.4)
__LINE__

The presumed line number (within the current source file) of the current source line (an integer literal).150
(1.5)
__STDC_HOSTED__

The integer literal 1 if the implementation is a hosted implementation or the integer literal 0 if it is not.
(1.6)
__STDCPP_DEFAULT_NEW_ALIGNMENT__

An integer literal of type std::size_t whose value is the alignment guaranteed by a call to operator new(std::size_t) or operator new[](std::size_t).

[ Note
:
Larger alignments will be passed to operator new(std::size_t, std::align_val_t), etc.

([expr.new]).
— end note
]
(1.7)
__TIME__

The time of translation of the source file: a character string literal of the form "hh:mm:ss" as in the time generated by the asctime function.

If the time of translation is not available, an implementation-defined valid time shall be supplied.
(1.8)
The names listed in Table 19 .

The macros defined in Table 19 shall be defined to the corresponding integer literal.

[ Note
:
Future versions of this International Standard might replace the values of these macros with greater values.
— end note
]

Table 19: Feature-test macros [tab:cpp.predefined.ft]

Macro name	Value
__cpp_aggregate_bases	201603L
__cpp_aggregate_nsdmi	201304L
__cpp_aggregate_paren_init	201902L
__cpp_alias_templates	200704L
__cpp_aligned_new	201606L
__cpp_attributes	200809L
__cpp_binary_literals	201304L
__cpp_capture_star_this	201603L
__cpp_char8_t	201811L
__cpp_concepts	201907L
__cpp_conditional_explicit	201806L
__cpp_constexpr	201907L
__cpp_constexpr_dynamic_alloc	201907L
__cpp_constexpr_in_decltype	201711L
__cpp_consteval	201811L
__cpp_constinit	201907L
__cpp_decltype	200707L
__cpp_decltype_auto	201304L
__cpp_deduction_guides	201907L
__cpp_delegating_constructors	200604L
__cpp_designated_initializers	201707L
__cpp_enumerator_attributes	201411L
__cpp_fold_expressions	201603L
__cpp_generic_lambdas	201707L
__cpp_guaranteed_copy_elision	201606L
__cpp_hex_float	201603L
__cpp_if_constexpr	201606L
__cpp_impl_coroutine	201902L
__cpp_impl_destroying_delete	201806L
__cpp_impl_three_way_comparison	201907L
__cpp_inheriting_constructors	201511L
__cpp_init_captures	201803L
__cpp_initializer_lists	200806L
__cpp_inline_variables	201606L
__cpp_lambdas	200907L
__cpp_modules	201907L
__cpp_namespace_attributes	201411L
__cpp_noexcept_function_type	201510L
__cpp_nontype_template_args	201911L
__cpp_nontype_template_parameter_auto	201606L
__cpp_nsdmi	200809L
__cpp_range_based_for	201603L
__cpp_raw_strings	200710L
__cpp_ref_qualifiers	200710L
__cpp_return_type_deduction	201304L
__cpp_rvalue_references	200610L
__cpp_sized_deallocation	201309L
__cpp_static_assert	201411L
__cpp_structured_bindings	201606L
__cpp_template_template_args	201611L
__cpp_threadsafe_static_init	200806L
__cpp_unicode_characters	200704L
__cpp_unicode_literals	200710L
__cpp_user_defined_literals	200809L
__cpp_using_enum	201907L
__cpp_variable_templates	201304L
__cpp_variadic_templates	200704L
__cpp_variadic_using	201611L

2

#

The following macro names are conditionally defined by the implementation:

(2.1)
__STDC__

Whether __STDC__ is predefined and if so, what its value is, are implementation-defined.
(2.2)
__STDC_MB_MIGHT_NEQ_WC__

The integer literal 1, intended to indicate that, in the encoding for wchar_t, a member of the basic character set need not have a code value equal to its value when used as the lone character in an ordinary character literal.
(2.3)
__STDC_VERSION__

Whether __STDC_VERSION__ is predefined and if so, what its value is, are implementation-defined.
(2.4)
__STDC_ISO_10646__

An integer literal of the form yyyymmL (for example, 199712L).

If this symbol is defined, then every character in the Unicode required set, when stored in an object of type wchar_t, has the same value as the code point of that character.

The Unicode required set consists of all the characters that are defined by ISO/IEC 10646, along with all amendments and technical corrigenda as of the specified year and month.
(2.5)
__STDCPP_STRICT_POINTER_SAFETY__

Defined, and has the value integer literal 1, if and only if the implementation has strict pointer safety .
(2.6)
__STDCPP_THREADS__

Defined, and has the value integer literal 1, if and only if a program can have more than one thread of execution .

3

#

The values of the predefined macros (except for __FILE__ and __LINE__) remain constant throughout the translation unit.

4

#

If any of the pre-defined macro names in this subclause, or the identifier defined, is the subject of a #define or a #undef preprocessing directive, the behavior is undefined.

Any other predefined macro names shall begin with a leading underscore followed by an uppercase letter or a second underscore.

15 Preprocessing directives [cpp]

15.11 Predefined macro names [cpp.predefined]