15 Preprocessing directives [cpp]

15.11 Predefined macro names [cpp.predefined]

The following macro names shall be defined by the implementation:
  • __cplusplus
    The integer literal 202302L.
    [Note 1: 
    Future revisions of C++ will replace the value of this macro with a greater value.
    — end note]
  • The names listed in Table 22.

    The macros defined in Table 22 shall be defined to the corresponding integer literal.
    [Note 2: 
    Future revisions of C++ might replace the values of these macros with greater values.
    — end note]
  • __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.
  • __FILE__
    The presumed name of the current source file (a character string literal).137
  • __LINE__
    The presumed line number (within the current source file) of the current source line (an integer literal).138
  • __STDC_HOSTED__
    The integer literal 1 if the implementation is a hosted implementation or the integer literal 0 if it is a freestanding implementation ([intro.compliance]).
  • __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 3: 
    Larger alignments will be passed to operator new(std​::​size_t, std​::​align_val_t), etc.
    — end note]
  • __STDCPP_FLOAT16_T__
    Defined as the integer literal 1 if and only if the implementation supports the ISO/IEC/IEEE 60559 floating-point interchange format binary16 as an extended floating-point type ([basic.extended.fp]).
  • __STDCPP_FLOAT32_T__
    Defined as the integer literal 1 if and only if the implementation supports the ISO/IEC/IEEE 60559 floating-point interchange format binary32 as an extended floating-point type.
  • __STDCPP_FLOAT64_T__
    Defined as the integer literal 1 if and only if the implementation supports the ISO/IEC/IEEE 60559 floating-point interchange format binary64 as an extended floating-point type.
  • __STDCPP_FLOAT128_T__
    Defined as the integer literal 1 if and only if the implementation supports the ISO/IEC/IEEE 60559 floating-point interchange format binary128 as an extended floating-point type.
  • __STDCPP_BFLOAT16_T__
    Defined as the integer literal 1 if and only if the implementation supports an extended floating-point type with the properties of the typedef-name std​::​bfloat16_t as described in [basic.extended.fp].
  • __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.
Table 22: 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_auto_cast
202110L
__cpp_binary_literals
201304L
__cpp_capture_star_this
201603L
__cpp_char8_t
202207L
__cpp_concepts
202002L
__cpp_conditional_explicit
201806L
__cpp_constexpr
202306L
__cpp_constexpr_dynamic_alloc
201907L
__cpp_constexpr_in_decltype
201711L
__cpp_consteval
202211L
__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_explicit_this_parameter
202110L
__cpp_fold_expressions
201603L
__cpp_generic_lambdas
201707L
__cpp_guaranteed_copy_elision
201606L
__cpp_hex_float
201603L
__cpp_if_consteval
202106L
__cpp_if_constexpr
201606L
__cpp_impl_coroutine
201902L
__cpp_impl_destroying_delete
201806L
__cpp_impl_three_way_comparison
201907L
__cpp_implicit_move
202207L
__cpp_inheriting_constructors
201511L
__cpp_init_captures
201803L
__cpp_initializer_lists
200806L
__cpp_inline_variables
201606L
__cpp_lambdas
200907L
__cpp_modules
201907L
__cpp_multidimensional_subscript
202211L
__cpp_named_character_escapes
202207L
__cpp_namespace_attributes
201411L
__cpp_noexcept_function_type
201510L
__cpp_nontype_template_args
201911L
__cpp_nontype_template_parameter_auto
201606L
__cpp_nsdmi
200809L
__cpp_pack_indexing
202311L
__cpp_placeholder_variables
202306L
__cpp_range_based_for
202211L
__cpp_raw_strings
200710L
__cpp_ref_qualifiers
200710L
__cpp_return_type_deduction
201304L
__cpp_rvalue_references
200610L
__cpp_size_t_suffix
202011L
__cpp_sized_deallocation
201309L
__cpp_static_assert
202306L
__cpp_static_call_operator
202207L
__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
The following macro names are conditionally defined by the implementation:
  • __STDC__
    Whether __STDC__ is predefined and if so, what its value is, are implementation-defined.
  • __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.
  • __STDC_VERSION__
    Whether __STDC_VERSION__ is predefined and if so, what its value is, are implementation-defined.
  • __STDC_ISO_10646__
    An integer literal of the form yyyymmL (for example, 199712L).
    Whether __STDC_ISO_10646__ is predefined and if so, what its value is, are implementation-defined.
  • __STDCPP_THREADS__
    Defined, and has the value integer literal 1, if and only if a program can have more than one thread of execution.
The values of the predefined macros (except for __FILE__ and __LINE__) remain constant throughout the translation unit.
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.
137)137)
The presumed source file name can be changed by the #line directive.
138)138)
The presumed line number can be changed by the #line directive.