C++ Compiler Warning Flags

Main

• -Wall
• -Wextra
• -Wpedantic
• -Wuninitialized
• -Wmissing-include-dirs
• -Wshadow
• -Wundef
• -Winvalid-pch

Extra

Control flow

• -Winit-self
• -Wswitch-enum -Wswitch-default
• -Wformat=2 -Wformat-nonliteral -Wformat-security -Wformat-y2k

Arithmetics

• -Wdouble-promotion
• -Wfloat-equal
• -Wpointer-arith

Cast and conversion

• -Wstrict-overflow=5
• -Wcast-qual
• -Wcast-align
• -Wconversion
• -Wpacked

Sanitizing

• -Wstrict-aliasing -fstrict-aliasing
• -Wredundant-decls
• -Wmissing-declarations
• -Wmissing-field-initializers

Security

• -Wwrite-strings
• -Wstack-protector -fstack-protector
• -Wpadded
• -Winline
• -Wdisabled-optimization

C specific

• -Waggregate-return
• -Wbad-function-cast
• -Wc++-compat

C++ specific

• -Wzero-as-null-pointer-constant
• -Wctor-dtor-privacy
• -Wold-style-cast
• -Woverloaded-virtual

GNU specific

• -Wlogical-op
• -Wstack-usage=1024 -fstack-usage # -Wframe-larger-than=1024
• -Wtrampolines
• -Wvector-operation-performance

GNU C++ specific

• -Wuseless-cast
• -Wnoexcept
• -Wstrict-null-sentinel

GNU >= 5.0.0

• -Wsuggest-final-types
• -Wsuggest-final-methods
• -Wsuggest-override

GNU >= 6.0.0

• -Wmisleading-indentation
• -Wshift-overflow
• -Wshift-negative-value
• -Wnull-dereference
• -Wshift-overflow=2
• -Wduplicated-cond

C++ GNU >= 6.0.0

• Detect virtual inheritance: -Wvirtual-inheritance
• Detect templates: -Wtemplates
• Detect multiple inheritance: -Wmultiple-inheritance

GNU >= 7.0.0

• -Wimplicit-fallthrough
• -Wunused-macros
• -Wformat-overflow=2
• -Wformat-truncation=2
• -Wstringop-overflow=4
• -Wduplicated-branches
• -Walloc-zero
• -Walloca

GNU >= 8.0.0

• -Wcast-align=strict
• -Wstringop-truncation
• -Wextra-semi

GNU >= 9.0.0

• -Wmultistatement-macros
• -Waddress-of-packed-member # enabled by default

C++ GNU >= 9.0.0

• -Wpessimizing-move # implied by -Wall
• -Wredundant-move # implied by -Wextra
• -Wdeprecated-copy # implied by -Wextra
• -Wdeprecated-copy-dtor # stricter: also warns when dtor is user-provided

GNU >= 10.0.0

• -Warith-conversion
• -Wstring-compare # implied by -Wextra

C++ GNU >= 10.0.0

• -Wmismatched-tags # off by default; eases porting to MSVC
• -Wredundant-tags # off by default; warns about redundant class-key/enum-key

GNU >= 11.0.0

• -Wmismatched-dealloc # enabled by default
• -Wsizeof-array-div # implied by -Wall
• -Wstringop-overread # enabled by default

C++ GNU >= 11.0.0

• -Wrange-loop-construct # implied by -Wall
• -Wmismatched-new-delete # implied by -Wall
• -Wvexing-parse # enabled by default
• -Wctad-maybe-unsupported # off by default; warns on CTAD without deduction guides
• -Wdeprecated-enum-enum-conversion # default in C++20
• -Wdeprecated-enum-float-conversion # default in C++20

GNU >= 12.0.0

• -Wbidi-chars # default: =unpaired; warns about misleading bidirectional control chars
• -Warray-compare # warns about comparison between two array-typed operands

GNU >= 13.0.0

• -Wxor-used-as-pow # warns when ^ is likely meant as exponentiation

C++ GNU >= 13.0.0

• -Wself-move # warns on std::move of a value to itself
• -Wdangling-reference # warns on references bound to temporaries whose lifetime ended

GNU >= 14.0.0

• -Walloc-size # warns about allocator-like functions with suspicious size arguments
• -Wcalloc-transposed-args # warns if calloc num/size arguments appear transposed

C++ GNU >= 14.0.0

• -Wnrvo # warns when named return value optimization is prevented
• -Welaborated-enum-base # warns about redundant enum-base in elaborated-type-specifier

GNU >= 15.0.0

• -Wheader-guard # implied by -Wall; warns about inconsistent header guard macros
• -Wleading-whitespace=spaces # warns about indentation style violations
• -Wtrailing-whitespace=spaces # warns about trailing whitespace

C++ GNU >= 15.0.0

• -Wdefaulted-function-deleted # warns when an explicitly defaulted function becomes deleted

Clang specific

Main

• -Werror=option-ignored
• -Warc-repeated-use-of-weak
• -Wbitfield-enum-conversion
• -Wc++11-compat-pedantic
• -Wclass-varargs
• -Wconditional-uninitialized
• -Wthread-safety

Mistakes

• -Wconsumed
• -Wdirect-ivar-access
• -Wdisabled-macro-expansion
• -Wembedded-directive
• -Wexit-time-destructors
• -Wexpansion-to-defined
• -Wformat-pedantic
• -Widiomatic-parentheses
• -Winconsistent-missing-destructor-override
• -Winfinite-recursion
• -Wlocal-type-template-args
• -Wloop-analysis
• -Wmethod-signatures
• -Wmismatched-tags
• -Wmissing-braces
• -Wmissing-prototypes
• -Wmissing-variable-declarations
• -Wmost
• -Wmove
• -Wnonportable-system-include-path
• -Wnull-pointer-arithmetic
• -Wover-aligned
• -Woverriding-method-mismatch
• -Wpch-date-time
• -Wpragmas
• -Wreserved-id-macro
• -Wreserved-user-defined-literal
• -Wretained-language-linkage
• -Wsemicolon-before-method-body
• -Wsometimes-uninitialized
• -Wstring-conversion
• -Wsuper-class-method-mismatch
• -Wtautological-compare
• -Wundefined-reinterpret-cast
• -Wunreachable-code
• -Wunreachable-code-break
• -Wunreachable-code-loop-increment
• -Wunreachable-code-return
• -Wvector-conversion

Sanitizing

• -Wcomma
• -Wduplicate-enum
• -Wduplicate-method-arg
• -Wduplicate-method-match
• -Wdynamic-exception-spec
• -Wempty-translation-unit
• -Wexplicit-ownership-type
• -Wignored-qualifiers
• -Wimplicit
• -Wkeyword-macro
• -Wnewline-eof
• -Wredundant-parens
• -Wstatic-in-inline
• -Wstrict-prototypes
• -Wweak-template-vtables
• -Wweak-vtables
• -Wzero-length-array

Arrays

• -Warray-bounds-pointer-arithmetic
• -Wextended-offsetof
• -Wflexible-array-extensions

Arithmetics

• -Wfloat-conversion
• -Wfloat-overflow-conversion
• -Wfloat-zero-conversion
• -Wshorten-64-to-32
• -Wsign-compare
• -Wsign-conversion

Advices

• -Wcomment
• -Wdocumentation
• -Wdocumentation-pedantic
• -Wglobal-constructors
• -Wgnu
• -Wheader-hygiene
• -Wunneeded-internal-declaration
• -Wunneeded-member-function
• -Wvla
• -Wsuggest-final-types
• -Wsuggest-final-methods
• -Wsuggest-override
• -Wshift-overflow
• -Wshift-negative-value
• -Wnull-dereference
• -Wunused-macros

Clang >= 6.0.0

• -Wextra-semi

Clang >= 7.0.0

• -Wc++98-compat-extra-semi # separated from -Wc++98-compat-pedantic

Clang >= 10.0.0

• -Wimplicit-int-float-conversion # warns on implicit float-to-int narrowing

Clang >= 11.0.0

• -Wpointer-to-int-cast # C: warns on cast of pointer to integer too small to hold all values
• -Wuninitialized-const-reference # grouped under -Wuninitialized
• -Wimplicit-const-int-float-conversion # grouped under -Wimplicit-int-float-conversion

Clang >= 12.0.0

• -Wdeprecated-volatile # C++20: warns on deprecated uses of volatile
• -Wnon-c-typedef-for-linkage # warns on C-style typedef used to give linkage to unnamed type

Clang >= 13.0.0

• -Wreserved-identifier # warns about identifiers reserved by the C/C++ standard

Clang >= 14.0.0

• -Wcast-function-type-strict # stricter version of -Wcast-function-type
• -Wbitfield-constant-conversion # warns on constant conversion in bitfield initializer

Clang >= 16.0.0

• -Wfuture-compat # warns about constructs that will be errors in future standards
• -Wsingle-bit-bitfield-constant-conversion # separated from -Wbitfield-constant-conversion

Clang >= 17.0.0

• -Wdeprecated-this-capture # C++20: warns on deprecated capture of this with default =

Clang >= 18.0.0

• -Wmissing-designated-field-initializers # sub-group of -Wmissing-field-initializers
• -Wc++23-compat # helps migrating code to C++23
• -Wc++2c-compat # helps migrating code to C++26

Clang >= 19.0.0

• -Wformat-signedness # warns when format requires unsigned but signed arg is passed (and vice versa)
• -Wpre-c11-compat # warns about C11 keywords used in pre-C11 language modes
• -Wtentative-definition-array # warns when a tentative array definition is assumed to have one element
• -Wunsafe-buffer-usage # warns about unsafe pointer/array operations (hardening)

References

• https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
• https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html
• https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html
• https://clang.llvm.org/docs/DiagnosticsReference.html
• https://gcc.gnu.org/gcc-9/changes.html
• https://gcc.gnu.org/gcc-10/changes.html
• https://gcc.gnu.org/gcc-11/changes.html
• https://gcc.gnu.org/gcc-12/changes.html
• https://gcc.gnu.org/gcc-13/changes.html
• https://gcc.gnu.org/gcc-14/changes.html
• https://gcc.gnu.org/gcc-15/changes.html