Clang Flag: -Wpedantic / -Wno-pedantic

The Clang compiler flags -Wpedantic and -Wno-pedantic are used to control the issuing of warnings regarding language standards compliance in source code being compiled with Clang. These flags are particularly useful for developers aiming to maintain portability or adhere strictly to language specifications by identifying language extensions or non-standard practices used in the code. - The -Wpedantic flag is used to enable warnings that alert the developer about language constructs that are not ISO C or ISO C++ standard compliant. This includes various extensions supported by Clang that may not be available in other compilers or might lead to unexpected behavior when compiled with strict standard compliance. When activated, -Wpedantic warns about non-standard practices, helping developers write more portable and standard-compliant code. This flag can be particularly useful when aiming for cross-compiler compatibility or adhering strictly to a language standard version. Enabling -Wpedantic may reveal reliance on compiler-specific or undefined behavior that could lead to bugs or incompatibilities. It encompasses a broad set of warnings related to extensions and language features that go beyond the standard, including but not limited to, GNU extensions, C99 or C11 features used in C++ code without explicit standard version flagging, or vice versa. Usage of -Wpedantic is recommended for projects where strict compliance with the language standard is necessary or beneficial. This might include libraries intended for wide distribution, cross-platform projects, or when trying to ensure compatibility with future standard versions. - -Wno-pedantic serves the opposite purpose, explicitly disabling these warnings. This might be useful in projects where specific language extensions or compiler-specific features are knowingly used and deemed beneficial or necessary. Use of this flag acknowledges the potential trade-offs in portability and standard compliance in favor of the practical benefits gained from the extensions in use. In sum, these flags offer developers control over the strictness of language standard adherence in their projects, aiding in the balancing act between portability, compatibility, and exploitation of compiler-specific benefits.

AI Generated

Subroups

• -Wc11-extensions (4 elements)
• -Wc++11-extra-semi (1 element)
• -Wc++11-long-long (1 element)
• -Wc++14-attribute-extensions (1 element)
• -Wc++14-binary-literal (1 element)
• -Wc++17-attribute-extensions (1 element)
• -Wc++20-attribute-extensions (1 element)
• -Wc++20-designator (1 element)
• -Wflexible-array-extensions (2 elements)
• -Wfuture-attribute-extensions (3 elements)
• -Wgnu-anonymous-struct (1 element)
• -Wgnu-auto-type (1 element)
• -Wgnu-binary-literal (1 element)
• -Wgnu-case-range (1 element)
• -Wgnu-complex-integer (1 element)
• -Wgnu-compound-literal-initializer (1 element)
• -Wgnu-conditional-omitted-operand (1 element)
• -Wgnu-empty-struct (3 elements)
• -Wgnu-flexible-array-initializer (1 element)
• -Wgnu-flexible-array-union-member (1 element)
• -Wgnu-imaginary-constant (1 element)
• -Wgnu-include-next (1 element)
• -Wgnu-label-as-value (2 elements)
• -Wgnu-line-marker (1 element)
• -Wgnu-null-pointer-arithmetic (1 element)
• -Wgnu-offsetof-extensions (1 element)
• -Wgnu-pointer-arith (3 elements)
• -Wgnu-redeclared-enum (1 element)
• -Wgnu-statement-expression (2 elements)
• -Wgnu-union-cast (1 element)
• -Wgnu-zero-line-directive (1 element)
• -Wgnu-zero-variadic-macro-arguments (2 elements)
• -Wkeyword-macro (1 element)
• -Wlong-long (2 elements)
• -Wmicrosoft-charize (1 element)
• -Wmicrosoft-comment-paste (1 element)
• -Wmicrosoft-cpp-macro (1 element)
• -Wmicrosoft-end-of-file (1 element)
• -Wmicrosoft-enum-value (1 element)
• -Wmicrosoft-fixed-enum (1 element)
• -Wmicrosoft-flexible-array (2 elements)
• -Wmicrosoft-redeclare-static (1 element)
• -Woverlength-strings (1 element)
• -Wvla-extension (1 element)
• -Wzero-length-array (1 element)
• -Wdollar-in-identifier-extension (1 element)
• -Wlanguage-extension-token (1 element)
• -Winvalid-utf8 (1 element)
• -Wdelimited-escape-sequence-extension (1 element)
• -Wimport-preprocessor-directive-pedantic (1 element)
• -Wembedded-directive (1 element)
• -Wempty-translation-unit (1 element)
• -Wnullability-extension (1 element)
• -Wfixed-enum-extension (1 element)
• -Wgeneric-type-extension (1 element)
• -Wbit-int-extension (1 element)
• -Wundefined-internal-type (1 element)
• -Wretained-language-linkage (1 element)
• -Wcomplex-component-init (1 element)
• -Wnested-anon-types (1 element)
• -Wc++23-default-comp-relaxed-constexpr (1 element)

Warnings/Remarks

Default Active (Deactivate with -Wno-pedantic)

None

Default Inactive (Activate with -Wpedantic)

ext_aggregate_init_not_constant	warning: initializer for aggregate is not a compile-time constant
ext_anonymous_record_with_type	warning: types declared in an anonymous struct union are a Microsoft extension
ext_anonymous_struct_union_qualified	warning: anonymous struct union cannot be 'B'
ext_array_size_conversion	warning: implicit conversion from array size expression of type A to integral enumeration type C is a C++11 extension
ext_auto_new_list_init	warning: ISO C++ standards before C++17 do not allow new expression for type A to use list-initialization
ext_c99_array_usage	warning: qualifier in static   array size     '[*] ' is a C99 feature
ext_c99_compound_literal	warning: compound literals are a C99-specific feature
ext_c99_feature	warning: 'A' is a C99 extension
ext_c99_flexible_array_member	warning: flexible array members are a C99 feature
ext_c99_variable_decl_in_for_loop	warning: variable declaration in for loop is a C99-specific feature
ext_c_empty_initializer	warning: use of an empty initializer is a C2x extension
ext_c_nullptr	warning: 'nullptr' is a C2x extension
ext_cast_fn_obj	warning: cast between pointer-to-function and pointer-to-object is an extension
ext_clang_diagnose_if	warning: 'diagnose_if' is a clang extension
ext_clang_enable_if	warning: 'enable_if' is a clang extension
ext_cxx11_enum_fixed_underlying_type	warning: enumeration types with a fixed underlying type are a C++11 extension
ext_designated_init	warning: designated initializers are a C99 feature
ext_dtor_name_ambiguous	warning: ISO C++ considers this destructor name lookup to be ambiguous
ext_dtor_named_in_wrong_scope	warning: ISO C++ requires the name after '::~' to be found in the same scope as the name before '::~'
ext_duplicate_declspec	warning: duplicate 'A' declaration specifier
ext_ellipsis_exception_spec	warning: exception specification of '...' is a Microsoft extension
ext_empty_fnmacro_arg	warning: empty macro arguments are a C99 feature
ext_enum_value_not_int	warning: ISO C restricts enumerator values to range of 'int' (A is too small large )
ext_enumerator_list_comma_c	warning: commas at the end of enumerator lists are a C99-specific feature
ext_enumerator_list_comma_cxx	warning: commas at the end of enumerator lists are a C++11 extension
ext_explicit_instantiation_without_qualified_id	warning: qualifier in explicit instantiation of A requires a template-id (a typedef is not permitted)
ext_expr_not_ice	warning: expression is not an integer integral constant expression; folding it to a constant is a GNU extension
ext_extern_template	warning: extern templates are a C++11 extension
ext_extra_semi	warning: extra ';' outside of a function inside a B inside instance variable list after member function definition
ext_forward_ref_enum	warning: ISO C forbids forward references to 'enum' types
ext_freestanding_complex	warning: complex numbers are an extension in a freestanding C99 implementation
ext_gnu_array_range	warning: use of GNU array range extension
ext_hex_constant_invalid	warning: hexadecimal floating constants are a C99 feature
ext_hex_literal_invalid	warning: hexadecimal floating literals are a C++17 feature
ext_ident_list_in_param	warning: type-less parameter names in function declaration
ext_in_class_initializer_non_constant	warning: in-class initializer for static data member is not a constant expression; folding it to a constant is a GNU extension
ext_integer_complement_complex	warning: ISO C does not support '~' for complex conjugation of A
ext_integer_increment_complex	warning: ISO C does not support '++'/'--' on complex integer type A
ext_internal_in_extern_inline_quiet	warning: static function variable B is used in an inline function with external linkage
ext_line_comment	warning: // comments are not allowed in this language
ext_main_used	warning: ISO C++ does not allow 'main' to be used by a program
ext_mixed_decls_code	warning: mixing declarations and code is a C99 extension
ext_multi_line_line_comment	warning: multi-line // comment
ext_named_variadic_macro	warning: named variadic macros are a GNU extension
ext_no_newline_eof	warning: no newline at end of file
ext_nonstandard_escape	warning: use of non-standard escape character '\A'
ext_ns_enum_attribute	warning: attributes on a namespace an enumerator declaration are a C++17 extension
ext_opencl_double_without_pragma	warning: Clang permits use of type 'double' regardless pragma if 'cl_khr_fp64' is supported
ext_pointer_to_const_ref_member_on_rvalue	warning: invoking a pointer to a 'const &' member function on an rvalue is a C++20 extension
ext_pp_bad_vaargs_use	warning: __VA_ARGS__ can only appear in the expansion of a C99 variadic macro
ext_pp_comma_expr	warning: comma operator in operand of #if
ext_pp_ident_directive	warning: #ident is a language extension
ext_pp_line_too_big	warning: C requires #line number to be less than A, allowed as extension
ext_pp_opencl_variadic_macros	warning: variadic macros are a Clang extension in OpenCL
ext_pp_warning_directive	warning: #warning is a C2x C++23 extension
ext_return_has_void_expr	warning: void function method block A should not return void expression
ext_rvalue_to_reference_access_ctor	warning: C++98 requires an accessible copy constructor for class C when binding a reference to a temporary; was private protected
ext_rvalue_to_reference_temp_copy_no_viable	warning: no viable constructor copying variable copying parameter initializing template parameter returning object initializing statement expression result throwing object copying member subobject copying array element allocating object copying temporary initializing base subobject initializing vector element capturing value of type B; C++98 requires a copy constructor when binding a reference to a temporary
ext_sizeof_alignof_function_type	warning: invalid application of 'A' to a function type
ext_sizeof_alignof_void_type	warning: invalid application of 'A' to a void type
ext_subscript_non_lvalue	warning: ISO C90 does not allow subscripting non-lvalue array
ext_thread_before	warning: '__thread' before 'A'
ext_typecheck_addrof_void	warning: ISO C forbids taking the address of an expression of type 'void'
ext_typecheck_cast_nonscalar	warning: C99 forbids casting nonscalar type A to the same type
ext_typecheck_comparison_of_fptr_to_void	warning: equality comparison between function pointer and void pointer (A and B)
ext_typecheck_cond_one_void	warning: C99 forbids conditional expressions with only one void side
ext_typecheck_convert_pointer_void_func	warning: assigning to A from B assigning to different types passing A to parameter of type B passing to parameter of different type returning A from a function with result type B returning from function with different return type converting A to type B converting between types initializing A with an expression of type B initializing with expression of different type sending A to parameter of type B sending to parameter of different type casting A to type B casting between types converts between void pointer and function pointer
ext_typecheck_ordered_comparison_of_pointer_and_zero	warning: ordered comparison between pointer and zero (A and B) is an extension
ext_variadic_macro	warning: variadic macros are a C99 feature
warn_defined_in_function_type_macro	warning: macro expansion producing 'defined' has undefined behavior
warn_ext_c2x_attributes	warning: [[]] attributes are a C2x extension
warn_ext_cxx11_attributes	warning: [[]] attributes are a C++11 extension
warn_format_conversion_argument_type_mismatch_pedantic	warning: format specifies type A but the argument has type underlying type B
warn_kern_is_method	warning: kernel function A is a member function; this may not be accepted by nvcc
warn_strict_prototypes	warning: a function block declaration without a prototype is deprecated in all versions of C
ext_anonymous_union	warning: anonymous unions are a C11 extension
ext_c11_anonymous_struct	warning: anonymous structs are a C11 extension
ext_c11_feature	warning: 'A' is a C11 extension
ext_typecheck_compare_complete_incomplete_pointers	warning: pointer comparisons before C11 need to be between two complete or two incomplete types; A is   in complete and B is   in complete
ext_extra_semi_cxx11	warning: extra ';' outside of a function is a C++11 extension
ext_cxx11_longlong	warning: 'long long' is a C++11 extension
ext_cxx14_attr	warning: use of the A attribute is a C++14 extension
ext_binary_literal_cxx14	warning: binary integer literals are a C++14 extension
ext_cxx17_attr	warning: use of the A attribute is a C++17 extension
ext_cxx20_attr	warning: use of the A attribute is a C++20 extension
ext_cxx_designated_init	warning: designated initializers are a C++20 extension
ext_flexible_array_in_array	warning: A may not be used as an array element due to flexible array member
ext_flexible_array_in_struct	warning: A may not be nested in a struct due to flexible array member
ext_cxx14_attr	warning: use of the A attribute is a C++14 extension
ext_cxx17_attr	warning: use of the A attribute is a C++17 extension
ext_cxx20_attr	warning: use of the A attribute is a C++20 extension
ext_gnu_anonymous_struct	warning: anonymous structs are a GNU extension
ext_auto_type	warning: '__auto_type' is a GNU extension
ext_binary_literal	warning: binary integer literals are a GNU extension
ext_gnu_case_range	warning: use of GNU case range extension
ext_integer_complex	warning: complex integer types are a GNU extension
ext_array_init_copy	warning: initialization of an array of type A from a compound literal of type B from a compound literal is a GNU extension
ext_gnu_conditional_expr	warning: use of GNU ?: conditional expression extension, omitting middle operand
ext_empty_struct_union	warning: empty struct union is a GNU extension
ext_flexible_array_empty_aggregate_gnu	warning: flexible array member A in otherwise empty struct interface union class enum is a GNU extension
ext_no_named_members_in_struct_union	warning: struct union without named members is a GNU extension
ext_flexible_array_init	warning: flexible array initialization is a GNU extension
ext_flexible_array_union_gnu	warning: flexible array member A in a union is a GNU extension
ext_imaginary_constant	warning: imaginary constants are a GNU extension
ext_pp_include_next_directive	warning: #include_next is a language extension
ext_gnu_address_of_label	warning: use of GNU address-of-label extension
ext_gnu_indirect_goto	warning: use of GNU indirect-goto extension
ext_pp_gnu_line_directive	warning: this style of line directive is a GNU extension
warn_gnu_null_ptr_arith	warning: arithmetic on a null pointer treated as a cast from integer to pointer is a GNU extension
ext_type_defined_in_offsetof	warning: defining a type within ' __builtin_offsetof offsetof ' is a Clang extension
ext_gnu_ptr_func_arith	warning: arithmetic on a   pointer   s to the   function type   s B   and D is a GNU extension
ext_gnu_subscript_void_type	warning: subscript of a pointer to void is a GNU extension
ext_gnu_void_ptr	warning: arithmetic on a   pointer   s to void is a GNU extension
ext_forward_ref_enum_def	warning: redeclaration of already-defined enum A is a GNU extension
ext_gnu_statement_expr	warning: use of GNU statement expression extension
ext_gnu_statement_expr_macro	warning: use of GNU statement expression extension from macro expansion
ext_typecheck_cast_to_union	warning: cast to union type is a GNU extension
ext_pp_line_zero	warning: #line directive with zero argument is a GNU extension
ext_missing_varargs_arg	warning: must specify at least one argument for '...' parameter of variadic macro
ext_paste_comma	warning: token pasting of ',' and __VA_ARGS__ is a GNU extension
warn_pp_macro_hides_keyword	warning: keyword is hidden by macro definition
ext_c99_longlong	warning: 'long long' is an extension when C99 mode is not enabled
ext_cxx11_longlong	warning: 'long long' is a C++11 extension
ext_charize_microsoft	warning: charizing operator #@ is a Microsoft extension
ext_comment_paste_microsoft	warning: pasting two '/' tokens into a '//' comment is a Microsoft extension
ext_pp_operator_used_as_macro_name	warning: C++ operator A (aka B) used as a macro name
ext_ctrl_z_eof_microsoft	warning: treating Ctrl-Z as end-of-file is a Microsoft extension
ext_enumerator_too_large	warning: enumerator value is not representable in the underlying type A
ext_ms_c_enum_fixed_underlying_type	warning: enumeration types with a fixed underlying type are a Microsoft extension
ext_flexible_array_empty_aggregate_ms	warning: flexible array member A in otherwise empty struct interface union class enum is a Microsoft extension
ext_flexible_array_union_ms	warning: flexible array member A in a union is a Microsoft extension
ext_static_non_static	warning: redeclaring non-static A as static is a Microsoft extension
ext_string_too_long	warning: string literal of length A exceeds maximum length B that C90 ISO C99 C++ compilers are required to support
ext_vla	warning: variable length arrays are a C99 feature
ext_typecheck_zero_array_size	warning: zero size arrays are an extension
ext_dollar_in_identifier	warning: '$' in identifier
ext_token_used	warning: extension used
warn_invalid_utf8_in_comment	warning: invalid UTF-8 in comment
ext_delimited_escape_sequence	warning: delimited named escape sequences are a Clang C++23 extension
ext_pp_import_directive	warning: #import is a language extension
ext_embedded_directive	warning: embedding a directive within macro arguments has undefined behavior
ext_empty_translation_unit	warning: ISO C requires a translation unit to contain at least one declaration
ext_nullability	warning: type nullability specifier A is a Clang extension
ext_clang_c_enum_fixed_underlying_type	warning: enumeration types with a fixed underlying type are a Clang extension
ext_generic_with_type_arg	warning: passing a type argument as the first operand to '_Generic' is a Clang extension
ext_bit_int	warning: '_BitInt' in C17 and earlier C++ is a Clang extension
ext_undefined_internal_type	warning: ISO C++ requires a definition in this translation unit for function variable B because its type does not have linkage
ext_retained_language_linkage	warning: friend function A retaining previous language linkage is an extension
ext_complex_component_init	warning: complex initialization specifying real and imaginary components is an extension
ext_anonymous_record_with_anonymous_type	warning: anonymous types declared in an anonymous struct union are an extension
ext_defaulted_comparison_constexpr_mismatch	warning: defaulted definition of equality three-way equality relational comparison operator three-way comparison operator that is declared constexpr consteval but   for which the corresponding implicit 'operator==' invokes a non-constexpr comparison function is a C++23 extension