C++ support

CLion incorporates two language engines, the built-in one and the Clangd-based one, both working in parallel.

The Clangd-based engine detects warnings and errors to be shown in the editor and provides quick-fixes, performs certain navigation actions, highlighting, and completion, while CLion's own engine is used for other code insight features like refactorings. You can adjust the scope of Clangd functionality in Clangd settings.

The following table shows how the two engines handle CLion features by default:

IDE feature	Language engine
Syntax highlighting	Clangd
Errors/warnings and quick-fixes	Clangd
Completion	Clangd only, both, or built-in only*
Formatting: ClangFormat	Clangd
Formatting: Code Style settings	Built-in engine
Navigation	Both **
Parameter hints	Clangd
Refactorings	Built-in engine

* - As selected in Clangd settings.

** - Both engines are used. Clangd helps with highlighting references at caret, Go to declaration, Go to definition, Quick documentation, Quick definition, Find Usages.

Language standards compliance

CLion fully supports C++11, C++14, C++17, and partially C++20.

Support for C++11 and C++14 is provided by the built-in engine. It also supports a part of the C++17 features, while the rest of them are provided by Clangd.

Support for the C++20 standard relies on Clangd except for parsing and refactorings (handled by the built-in engine). Besides, the built-in engine extends the Clangd's support for C++20 Concepts (see the dedicated article for details).

The tables below give an overview of the standards support status, and the details of C++20 and C+17 support.

Standard	Clangd (CXX_status)	Built-in engine
C++20, C++2b	Partial support	Parsing and refactorings for the features supported by Clangd Extended support for Concepts (based on Clangd): custom highlighting, code completion, dedicated inspections, Rename refactoring, navigation actions like Go to Definition and Find Usages.
C++17	Full support starting Clang 5	Partial support
C++14	Full support	Full support
C++11	Full support	Full support

C++2b

Language feature	Clang support status	Error highlighting and quick-fixes	Completion	Navigation	Parsing	Refactorings
Literal suffix `uz`, `z` for `size_t`, `ssize_t` (P0330R8)	Partially	-	-	-	-	-
Make `()` in lambdas optional in all cases (P1102R2)	Partially	-	-	-	-	-
Simpler implicit move (P2266R1)	Partially	-	-	-	-	-
`if consteval` (P1938R3)	-	-	-	-	-	-
Allow duplicate attributes (P2556R1)	Partial	-	-	-	-	-
Narrowing contextual conversions to bool (P1401R5)	Partial	-	-	-	-	-
Trimming whitespaces before line splicing (P2223R2)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Make declaration order layout mandated (P1874R4)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
C++ identifier syntax using UAX 31 (P1949R7)	Partial	-	-	-	-	-
Mixed string literal concatenation (P2201R1)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-

C++20

Language feature	Clang support status	Error highlighting and quick-fixes	Completion	Navigation	Parsing	Refactorings
Default member initializers for bit-fields (P0683R1)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
`const&`-qualified pointers to members (P0704R1)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Allow lambda-capture `[=, this]` (P0409R2)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
`__VA_OPT__` for preprocessor comma elision (P0306R4, P1042R1)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Designated initializers (P0329R4)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
template-parameter-list for generic lambdas (P0428R2)	+	Clangd	Clangd	Mixed	Built-in engine	-
Concepts: P0734R0 P0857R0 P1084R2 P1141R2 P1616R1 P1452R2	+	Clangd	Clangd	Mixed	Built-in engine	Built-in engine, Rename only
Concepts: P0848R3 P1972R0 P1980R0 P2103R0 P2092R0 P2113R0	-	-	-	-	-	-
Range-based for statements with initializer (P0614R1)	+	Clangd	Clangd	Mixed	Built-in engine	Built-in engine
ADL and function templates that are not visible (P0846R0)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
`const` mismatch with defaulted copy constructor (P0641R2)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Consistent comparison (`operator<=>`): P0515R3 P0905R1 P1120R0 P1185R2 P1186R3 P1630R1 P1946R0 P1959R0	+	Clangd	Clangd	Mixed	Built-in engine	-
Consistent comparison (`operator<=>`): P2002R1	Partial	-	-	-	-	-
Consistent comparison (`operator<=>`): P2085R0	-	-	-	-	-	-
Access checking on specializations (P0692R1)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Default constructible and assignable stateless lambdas (P0624R2)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Lambdas in unevaluated contexts (P0315R4)	Partially (doesn't implement `temp.deduct/9`)	Clangd	Clangd	Mixed, relying on Clangd	-	-
`[[no_unique_address]]` attribute (P0840R2)	+	Clangd	Clangd	Mixed	Built-in engine	-
`[[likely]]` and `[[unlikely]]` attributes (P0479R5)	+	Built-in engine	Built-in engine	Built-in engine	Built-in engine	-
typename optional in more contexts (P0634R3)	-	-	-	-	-	-
Pack expansion in lambda init-capture (P0780R2)	+	Clangd	Clangd	Mixed	Built-in engine	-
Class types as non-type template parameters (P0732R2, P1907R1	Partial	Clangd	Clang	-	-	-
Destroying operator delete (P0722R3)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Relaxations of constexpr restrictions (P1064R0, P1002R1, P1327R1, P1330R0, P1331R2, P1668R1, P0784R7)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Prohibit aggregates with user-declared constructors (P1008R1)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Feature test macros (P0941R2)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
`explicit(bool)` (P0892R2)	+	Clangd	Clangd	Mixed	Built-in engine	Built-in engine
Signed integers are two's complement (P1236R1)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
`char8_t` (P0482R6)	+	Clangd	Clangd	Mixed	Built-in engine	-
Immediate functions (`consteval`) (P1073R3, P1937R2)	+	Clangd	Clangd	Mixed	Built-in engine	-
`std::is_constant_evaluated` (P0595R2)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Nested inline namespaces (P1094R2)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Structured binding extensions (P1091R3, P1381R1)	Partially	-	-	-	-	-
Stronger Unicode requirements (P1041R4, P1139R2)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Parenthesized initialization of aggregates (P0960R3, P1975R0)	-	-	-	-	-	-
Modules: P1766R1 (DR)	+ (Clang 11)	-	-	-	-	-
Modules: (P1874R1), P2115R0, P1103R3	Partially	-	-	-	-	-
Modules: P1979R0, P1779R3, P1857R3, P1815R2, P1811R0, P1703R1	-	-	-	-	-	-
Coroutines (P0912R5)	Partially	Clangd	Clangd	Mixed	Built-in engine	-
Deprecate `a[b,c]` (P1161R3)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Deprecate some problematic uses of `volatile` (P1152R4)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
`[[nodiscard("with reason")]]` (P1301R4)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
`using enum` (P1099R5)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-
Class template argument deduction for aggregates (P1816R0, P2082R1)	-	-	-	-	-	-
Class template argument deduction for alias templates (P1814R0)	-	-	-	-	-	-
Permit conversions to arrays of unknown bound (P0388R4)	-	-	-	-	-	-
`constinit` (P1143R2)	+	Clangd	Clangd	Mixed	Built-in engine	-
Pseudo-destructors end object lifetimes P0593R6 (DR)	+ (Clang 11)	-	-	-	-	-
More implicit moves P1825R0 (DR)	+	Clangd	Clangd	Mixed, relying on Clangd	-	-

C++17

Language feature	Error highlighting and quick-fixes	Completion	Navigation	Refactorings
auto non-type parameters	Clangd	Clangd	Mixed, relying on Clangd	-
UTF-8 character literals	Clangd	Clangd	Mixed, relying on Clangd	-
lambda capture of *this	Clangd	Clangd	Mixed, relying on Clangd	-
[[nodiscard]] attribute	Clangd	Clangd	Mixed, relying on Clangd	-
[[fallthrough]] attribute	Clangd	Clangd	Mixed, relying on Clangd	-
[[maybe_unused]] attribute	Clangd	Clangd	Mixed, relying on Clangd	-
'noexcept' as part of a function type	Clangd	Clangd	Mixed, relying on Clangd	-
one-argument static assert	Clangd	Clangd	Mixed, relying on Clangd	-
if constexpr	Clangd	Clangd	Mixed, relying on Clangd	-
inline variables	Clangd	Clangd	Mixed, relying on Clangd	-
new rules for auto deduction from braced-init-list	Clangd	Clangd	Mixed, relying on Clangd	-
constexpr lambdas	Clangd	Clangd	Mixed, relying on Clangd	-
nested namespace definition	Clangd	Clangd only, both, or built-in only *	Mixed **	Build-in engine
fold expressions	Clangd	Clangd only, both, or built-in only *	Mixed **	-
class template argument deduction	Clangd	Clangd only, both, or built-in only *	Mixed **	-
__has_include	Clangd	Clangd	-	-

* - As selected in Clangd settings.

** - Both engines are used. Clangd helps with highlighting references at caret, Go to declaration, Go to definition, Quick documentation, Quick definition, Find Usages.

C++ code inspections

CLion performs static analysis on your C/C++ code using a set of inspections, configurable in Settings / Preferences | Editor | Inspections | C/C++. Some of the C/C++ inspections are provided by Clangd, while the others work as part of the built-in engine.

The table below shows which engine is used for a particular inspection or a set of inspections. Note that Objective-C checks are not listed except for those with similar Clang diagnostics.

Inspection	Provided by
Data flow analysis	Clangd
Functions	Build-in engine
General: Argument selection defects	Clangd
General: Clang-tidy	Clangd or built-in, as selected
General: Unconstrained variable type	Built-in engine (based on Clangd)
General: Empty declaration or statement	Clangd
General: Format specifiers	For C/C++, this check is covered by Clang’s -Wformat diagnostic.
General: `'='` in conditional expression	For C/C++, this check is covered by Clang’s -Wparentheses diagnostic.
General: Inconsistent naming	Built-in engine
General: Missing switch case	For C/C++, this check is covered by Clang’s -Wswitch diagnostic.
General: Simplifiable statement	Clangd
General: Virtual call from constructor or destructor	Clangd
Unused code: Unused concept	Built-in engine (based on Clangd)
Unused code: Unused expression result	For C/C++, this check is covered by Clangd’s DFA.
Unused code: Unused global declaration	Clangd
Unused code: Unused include directive	Clangd
Unused code: Unused macro	Clangd
Unused code: Unused struct	Clangd
Unused code: Unused template parameter	Clangd
Unused code: Unused type alias	Clangd

Last modified: 29 September 2021