There is a discussion thread on reddit about the flags being used for c code compilation, https://www.reddit.com/r/C_Programming/comments/ievcev/what_is_the_most_effective_set_of_gcc_warning/
CFLAGS += -std=c99 -Wpedantic -pedantic-errors
CFLAGS += -Werror
CFLAGS += -Wall
CFLAGS += -Wextra
CFLAGS += -Waggregate-return
CFLAGS += -Wbad-function-cast
CFLAGS += -Wcast-align
CFLAGS += -Wcast-qual
CFLAGS += -Wdeclaration-after-statement
CFLAGS += -Wfloat-equal
CFLAGS += -Wformat=2
CFLAGS += -Wlogical-op
CFLAGS += -Wmissing-declarations
CFLAGS += -Wmissing-include-dirs
CFLAGS += -Wmissing-prototypes
CFLAGS += -Wnested-externs
CFLAGS += -Wpointer-arith
CFLAGS += -Wredundant-decls
CFLAGS += -Wsequence-point
CFLAGS += -Wshadow
CFLAGS += -Wstrict-prototypes
CFLAGS += -Wswitch
CFLAGS += -Wundef
CFLAGS += -Wunreachable-code
CFLAGS += -Wunused-but-set-parameter
CFLAGS += -Wwrite-strings
To get details of the each flag use "$ man gcc"
The info for each flag given in man page is as below
- -Wpedantic
Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that use forbidden extensions, and some other programs that do not follow ISO C and ISO C++. For ISO C, follows the version of the ISO C standard specified by any -std option used. Valid ISO C and ISO C++ programs should compile properly with or without this option (though a rare few require -ansi or a -std option specifying the required version of ISO C). However, without this option, certain GNU extensions and traditional C and C++ features are supported as well. With this option, they are rejected.
- -Wall
-Wall turns on the following warning flags: -Waddress -Warray-bounds=1 (only with -O2) -Wbool-compare -Wbool-operation -Wc++11-compat -Wc++14-compat -Wcatch-value (C++ and Objective-C++ only) -Wchar-subscripts -Wcomment -Wduplicate-decl-specifier (C and Objective-C only) -Wenum-compare (in C/ObjC; this is on by default in C++) -Wformat -Wint-in-bool-context -Wimplicit (C and Objective-C only) -Wimplicit-int (C and Objective-C only) -Wimplicit-function-declaration (C and Objective-C only) -Winit-self (only for C++) -Wlogical-not-parentheses -Wmain (only for C/ObjC and unless -ffreestanding) -Wmaybe-uninitialized -Wmemset-elt-size -Wmemset-transposed-args -Wmisleading-indentation (only for C/C++) -Wmissing-attributes -Wmissing-braces(only for C/ObjC) -Wmultistatement-macros -Wnarrowing (only for C++) -Wnonnull -Wnonnull-compare -Wopenmp-simd -Wparentheses -Wpessimizing-move (only for C++) -Wpointer-sign -Wreorder -Wrestrict -Wreturn-type -Wsequence-point -Wsign-compare (only in C++) -Wsizeof-pointer-div -Wsizeof-pointer-memaccess -Wstrict-aliasing -Wstrict-overflow=1 -Wswitch -Wtautological-compare -Wtrigraphs -Wuninitialized -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value -Wunused-variable -Wvolatile-register-var
- -Wextra
-Wclobbered -Wcast-function-type -Wdeprecated-copy (C++ only) -Wempty-body -Wignored-qualifiers -Wimplicit-fallthrough=3 -Wmissing-field-initializers -Wmissing-parameter-type (C only) -Wold-style-declaration (C only) -Woverride-init -Wsign-compare (C only) -Wredundant-move (only for C++) -Wtype-limits -Wuninitialized -Wshift-negative-value (in C++03 and in C99 and newer) -Wunused-parameter (only with -Wunused or -Wall) -Wunused-but-set-parameter (only with -Wunused or -Wall)
- -Waggregate-return
Warn if any functions that return structures or unions are defined or called. (In languages where you can return an array, this also elicits a warning.)
- -Wbad-function-cast (C and Objective-C only)
Warn when a function call is cast to a non-matching type. For example, warn if a call to a function returning an integer type is cast to a pointer type.
- -Wcast-align
Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a "char *" is cast to an "int *" on machines where integers can only be accessed at two- or four-byte boundaries.
- -Wcast-qual
Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a "const char *" is cast to an ordinary "char *".
- -Wfloat-equal
Warn if floating-point values are used in equality comparisons.
- -Wformat=2
Enable -Wformat plus additional format checks. Currently equivalent to -Wformat -Wformat-nonliteral -Wformat-security -Wformat-y2k.
- -Wlogical-op
Warn about suspicious uses of logical operators in expressions. This includes using logical operators in contexts where a bit-wise operator is likely to be expected.
- -Wmissing-declarations
Warn if a global function is defined without a previous declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files.
- -Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)
Warn if a user-supplied include directory does not exist.
- -Wmissing-prototypes (C and Objective-C only)
Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. Use this option to detect global functions that do not have a matching prototype declaration in a header file. This option is not valid for C++ because all function declarations provide prototypes and a non-matching declaration declares an overload rather than conflict with an earlier declaration. Use -Wmissing-declarations to detect missing declarations in C++.
- -Wnested-externs (C and Objective-C only)
Warn if an "extern" declaration is encountered within a function.
- -Wnested-externs (C and Objective-C only)
Warn if an "extern" declaration is encountered within a function.
- -Wpointer-arith
Warn about anything that depends on the "size of" a function type or of "void". GNU C assigns these types a size of 1, for convenience in calculations with "void *" pointers and pointers to functions. In C++, warn also when an arithmetic operation involves "NULL". This warning is also enabled by -Wpedantic.
- -Wredundant-decls
Warn if anything is declared more than once in the same scope, even in cases where multiple declaration is valid and changes nothing.
- -Wsequence-point
Warn about code that may have undefined semantics because of violations of sequence point rules in the C and C++ standards.
- -Wshadow
Warn whenever a local variable or type declaration shadows another variable, parameter, type, class member (in C++), or instance variable (in Objective-C) or whenever a built-in function is shadowed. Note that in C++, the compiler warns if a local variable shadows an explicit typedef, but not if it shadows a struct/class/enum. Same as -Wshadow=global.
- -Wstrict-prototypes (C and Objective-C only)
Warn if a function is declared or defined without specifying the argument types. (An old-style function definition is permitted without a warning if preceded by a declaration that specifies the argument types.)
- -Wundef
Warn if an undefined identifier is evaluated in an "#if" directive. Such identifiers are replaced with zero.
