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START-INFO-DIR-ENTRY
* gcc: (gcc). The GNU Compiler Collection.
END-INFO-DIR-ENTRY
This file documents the use and the internals of the GNU compiler.
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File: gcc.info, Node: C++ Dialect Options, Next: Warning Options, Prev: C Dialect Options, Up: Invoking GCC
Options Controlling C++ Dialect
===============================
This section describes the command-line options that are only
meaningful for C++ programs; but you can also use most of the GNU
compiler options regardless of what language your program is in. For
example, you might compile a file `firstClass.C' like this:
g++ -g -frepo -O -c firstClass.C
In this example, only `-frepo' is an option meant only for C++
programs; you can use the other options with any language supported by
GCC.
Here is a list of options that are *only* for compiling C++ programs:
`-fno-access-control'
Turn off all access checking. This switch is mainly useful for
working around bugs in the access control code.
`-fcheck-new'
Check that the pointer returned by `operator new' is non-null
before attempting to modify the storage allocated. The current
Working Paper requires that `operator new' never return a null
pointer, so this check is normally unnecessary.
An alternative to using this option is to specify that your
`operator new' does not throw any exceptions; if you declare it
`throw()', g++ will check the return value. See also `new
(nothrow)'.
`-fconserve-space'
Put uninitialized or runtime-initialized global variables into the
common segment, as C does. This saves space in the executable at
the cost of not diagnosing duplicate definitions. If you compile
with this flag and your program mysteriously crashes after
`main()' has completed, you may have an object that is being
destroyed twice because two definitions were merged.
This option is no longer useful on most targets, now that support
has been added for putting variables into BSS without making them
common.
`-fdollars-in-identifiers'
Accept `$' in identifiers. You can also explicitly prohibit use of
`$' with the option `-fno-dollars-in-identifiers'. (GNU C allows
`$' by default on most target systems, but there are a few
exceptions.) Traditional C allowed the character `$' to form part
of identifiers. However, ANSI C and C++ forbid `$' in identifiers.
`-fno-elide-constructors'
The C++ standard allows an implementation to omit creating a
temporary which is only used to initialize another object of the
same type. Specifying this option disables that optimization, and
forces g++ to call the copy constructor in all cases.
`-fexternal-templates'
Cause template instantiations to obey `#pragma interface' and
`implementation'; template instances are emitted or not according
to the location of the template definition. *Note Template
Instantiation::, for more information.
This option is deprecated.
`-falt-external-templates'
Similar to -fexternal-templates, but template instances are
emitted or not according to the place where they are first
instantiated. *Note Template Instantiation::, for more
information.
This option is deprecated.
`-ffor-scope'
`-fno-for-scope'
If -ffor-scope is specified, the scope of variables declared in a
for-init-statement is limited to the `for' loop itself, as
specified by the draft C++ standard. If -fno-for-scope is
specified, the scope of variables declared in a for-init-statement
extends to the end of the enclosing scope, as was the case in old
versions of gcc, and other (traditional) implementations of C++.
The default if neither flag is given to follow the standard, but
to allow and give a warning for old-style code that would
otherwise be invalid, or have different behavior.
`-fno-gnu-keywords'
Do not recognize `classof', `headof', `signature', `sigof' or
`typeof' as a keyword, so that code can use these words as
identifiers. You can use the keywords `__classof__',
`__headof__', `__signature__', `__sigof__', and `__typeof__'
instead. `-ansi' implies `-fno-gnu-keywords'.
`-fguiding-decls'
Treat a function declaration with the same type as a potential
function template instantiation as though it declares that
instantiation, not a normal function. If a definition is given
for the function later in the translation unit (or another
translation unit if the target supports weak symbols), that
definition will be used; otherwise the template will be
instantiated. This behavior reflects the C++ language prior to
September 1996, when guiding declarations were removed.
This option implies `-fname-mangling-version-0', and will not work
with other name mangling versions. Like all options that change
the ABI, all C++ code, *including libgcc.a* must be built with the
same setting of this option.
`-fhandle-signatures'
Recognize the `signature' and `sigof' keywords for specifying
abstract types. The default (`-fno-handle-signatures') is not to
recognize them. *Note Type Abstraction using Signatures: C++
Signatures.
`-fhonor-std'
Treat the `namespace std' as a namespace, instead of ignoring it.
For compatibility with earlier versions of g++, the compiler will,
by default, ignore `namespace-declarations', `using-declarations',
`using-directives', and `namespace-names', if they involve `std'.
`-fhuge-objects'
Support virtual function calls for objects that exceed the size
representable by a `short int'. Users should not use this flag by
default; if you need to use it, the compiler will tell you so.
This flag is not useful when compiling with -fvtable-thunks.
Like all options that change the ABI, all C++ code, *including
libgcc* must be built with the same setting of this option.
`-fno-implicit-templates'
Never emit code for non-inline templates which are instantiated
implicitly (i.e. by use); only emit code for explicit
instantiations. *Note Template Instantiation::, for more
information.
`-fno-implicit-inline-templates'
Don't emit code for implicit instantiations of inline templates,
either. The default is to handle inlines differently so that
compiles with and without optimization will need the same set of
explicit instantiations.
`-finit-priority'
Support `__attribute__ ((init_priority (n)))' for controlling the
order of initialization of file-scope objects. On ELF targets,
this requires GNU ld 2.10 or later.
`-fno-implement-inlines'
To save space, do not emit out-of-line copies of inline functions
controlled by `#pragma implementation'. This will cause linker
errors if these functions are not inlined everywhere they are
called.
`-fname-mangling-version-N'
Control the way in which names are mangled. Version 0 is
compatible with versions of g++ before 2.8. Version 1 is the
default. Version 1 will allow correct mangling of function
templates. For example, version 0 mangling does not mangle
foo<int, double> and foo<int, char> given this declaration:
template <class T, class U> void foo(T t);
Like all options that change the ABI, all C++ code, *including
libgcc* must be built with the same setting of this option.
`-foperator-names'
Recognize the operator name keywords `and', `bitand', `bitor',
`compl', `not', `or' and `xor' as synonyms for the symbols they
refer to. `-ansi' implies `-foperator-names'.
`-fno-optional-diags'
Disable diagnostics that the standard says a compiler does not
need to issue. Currently, the only such diagnostic issued by g++
is the one for a name having multiple meanings within a class.
`-fpermissive'
Downgrade messages about nonconformant code from errors to
warnings. By default, g++ effectively sets `-pedantic-errors'
without `-pedantic'; this option reverses that. This behavior and
this option are superceded by `-pedantic', which works as it does
for GNU C.
`-frepo'
Enable automatic template instantiation. This option also implies
`-fno-implicit-templates'. *Note Template Instantiation::, for
more information.
`-fno-rtti'
Disable generation of the information used by C++ runtime type
identification features (`dynamic_cast' and `typeid'). If you
don't use those parts of the language (or exception handling,
which uses `dynamic_cast' internally), you can save some space by
using this flag.
`-fstrict-prototype'
Within an `extern "C"' linkage specification, treat a function
declaration with no arguments, such as `int foo ();', as declaring
the function to take no arguments. Normally, such a declaration
means that the function `foo' can take any combination of
arguments, as in C. `-pedantic' implies `-fstrict-prototype'
unless overridden with `-fno-strict-prototype'.
Specifying this option will also suppress implicit declarations of
functions.
This flag no longer affects declarations with C++ linkage.
`-fsquangle'
`-fno-squangle'
`-fsquangle' will enable a compressed form of name mangling for
identifiers. In particular, it helps to shorten very long names by
recognizing types and class names which occur more than once,
replacing them with special short ID codes. This option also
requires any C++ libraries being used to be compiled with this
option as well. The compiler has this disabled (the equivalent of
`-fno-squangle') by default.
Like all options that change the ABI, all C++ code, *including
libgcc.a* must be built with the same setting of this option.
`-ftemplate-depth-N'
Set the maximum instantiation depth for template classes to N. A
limit on the template instantiation depth is needed to detect
endless recursions during template class instantiation. ANSI/ISO
C++ conforming programs must not rely on a maximum depth greater
than 17.
`-fthis-is-variable'
Permit assignment to `this'. The incorporation of user-defined
free store management into C++ has made assignment to `this' an
anachronism. Therefore, by default it is invalid to assign to
`this' within a class member function; that is, GNU C++ treats
`this' in a member function of class `X' as a non-lvalue of type
`X *'. However, for backwards compatibility, you can make it
valid with `-fthis-is-variable'.
`-fvtable-thunks=THUNKS-VERSION'
Use `thunks' to implement the virtual function dispatch table
(`vtable'). The traditional (cfront-style) approach to
implementing vtables was to store a pointer to the function and two
offsets for adjusting the `this' pointer at the call site. Newer
implementations store a single pointer to a `thunk' function which
does any necessary adjustment and then calls the target function.
The original implementation of thunks (version 1) had a bug
regarding virtual base classes; this bug is fixed with version 2
of the thunks implementation. With setting the version to 2,
compatibility to the version 1 thunks is provided, at the cost of
extra machine code. Version 3 does not include this compatibility.
This option also enables a heuristic for controlling emission of
vtables; if a class has any non-inline virtual functions, the
vtable will be emitted in the translation unit containing the
first one of those.
Like all options that change the ABI, all C++ code, *including
libgcc.a* must be built with the same setting of this option. Since
version 1 and version 2 are also incompatible (for classes with
virtual bases defining virtual functions), all code must also be
compiled with the same version.
In this version of gcc, there are no targets for which version 2
thunks are the default. On all targets, not giving the option
will use the traditional implementation, and -fvtable-thunks will
produce version 2 thunks.
`-nostdinc++'
Do not search for header files in the standard directories
specific to C++, but do still search the other standard
directories. (This option is used when building the C++ library.)
In addition, these optimization, warning, and code generation options
have meanings only for C++ programs:
`-fno-default-inline'
Do not assume `inline' for functions defined inside a class scope.
*Note Options That Control Optimization: Optimize Options. Note
that these functions will have linkage like inline functions; they
just won't be inlined by default.
`-Wctor-dtor-privacy (C++ only)'
Warn when a class seems unusable, because all the constructors or
destructors in a class are private and the class has no friends or
public static member functions.
`-Wnon-virtual-dtor (C++ only)'
Warn when a class declares a non-virtual destructor that should
probably be virtual, because it looks like the class will be used
polymorphically.
`-Wreorder (C++ only)'
Warn when the order of member initializers given in the code does
not match the order in which they must be executed. For instance:
struct A {
int i;
int j;
A(): j (0), i (1) { }
};
Here the compiler will warn that the member initializers for `i'
and `j' will be rearranged to match the declaration order of the
members.
The following `-W...' options are not affected by `-Wall'.
`-Weffc++ (C++ only)'
Warn about violations of various style guidelines from Scott
Meyers' `Effective C++' books. If you use this option, you should
be aware that the standard library headers do not obey all of
these guidelines; you can use `grep -v' to filter out those
warnings.
`-Wno-deprecated (C++ only)'
Do not warn about usage of deprecated features. *Note Deprecated
Features::.
`-Wno-non-template-friend (C++ only)'
Disable warnings when non-templatized friend functions are declared
within a template. With the advent of explicit template
specification support in g++, if the name of the friend is an
unqualified-id (ie, `friend foo(int)'), the C++ language
specification demands that the friend declare or define an
ordinary, nontemplate function. (Section 14.5.3). Before g++
implemented explicit specification, unqualified-ids could be
interpreted as a particular specialization of a templatized
function. Because this non-conforming behavior is no longer the
default behavior for g++, `-Wnon-template-friend' allows the
compiler to check existing code for potential trouble spots, and
is on by default. This new compiler behavior can also be turned
off with the flag `-fguiding-decls', which activates the older,
non-specification compiler code, or with
`-Wno-non-template-friend' which keeps the conformant compiler
code but disables the helpful warning.
`-Wold-style-cast (C++ only)'
Warn if an old-style (C-style) cast is used within a C++ program.
The new-style casts (`static_cast', `reinterpret_cast', and
`const_cast') are less vulnerable to unintended effects.
`-Woverloaded-virtual (C++ only)'
Warn when a derived class function declaration may be an error in
defining a virtual function. In a derived class, the definitions
of virtual functions must match the type signature of a virtual
function declared in the base class. With this option, the
compiler warns when you define a function with the same name as a
virtual function, but with a type signature that does not match any
declarations from the base class.
`-Wno-pmf-conversions (C++ only)'
Disable the diagnostic for converting a bound pointer to member
function to a plain pointer.
`-Wsign-promo (C++ only)'
Warn when overload resolution chooses a promotion from unsigned or
enumeral type to a signed type over a conversion to an unsigned
type of the same size. Previous versions of g++ would try to
preserve unsignedness, but the standard mandates the current
behavior.
`-Wsynth (C++ only)'
Warn when g++'s synthesis behavior does not match that of cfront.
For instance:
struct A {
operator int ();
A& operator = (int);
};
main ()
{
A a,b;
a = b;
}
In this example, g++ will synthesize a default `A& operator =
(const A&);', while cfront will use the user-defined `operator ='.
File: gcc.info, Node: Warning Options, Next: Debugging Options, Prev: C++ Dialect Options, Up: Invoking GCC
Options to Request or Suppress Warnings
=======================================
Warnings are diagnostic messages that report constructions which are
not inherently erroneous but which are risky or suggest there may have
been an error.
You can request many specific warnings with options beginning `-W',
for example `-Wimplicit' to request warnings on implicit declarations.
Each of these specific warning options also has a negative form
beginning `-Wno-' to turn off warnings; for example, `-Wno-implicit'.
This manual lists only one of the two forms, whichever is not the
default.
These options control the amount and kinds of warnings produced by
GCC:
`-fsyntax-only'
Check the code for syntax errors, but don't do anything beyond
that.
`-pedantic'
Issue all the warnings demanded by strict ANSI C and ISO C++;
reject all programs that use forbidden extensions.
Valid ANSI C and ISO C++ programs should compile properly with or
without this option (though a rare few will require `-ansi').
However, without this option, certain GNU extensions and
traditional C and C++ features are supported as well. With this
option, they are rejected.
`-pedantic' does not cause warning messages for use of the
alternate keywords whose names begin and end with `__'. Pedantic
warnings are also disabled in the expression that follows
`__extension__'. However, only system header files should use
these escape routes; application programs should avoid them.
*Note Alternate Keywords::.
This option is not intended to be useful; it exists only to satisfy
pedants who would otherwise claim that GCC fails to support the
ANSI standard.
Some users try to use `-pedantic' to check programs for strict ANSI
C conformance. They soon find that it does not do quite what they
want: it finds some non-ANSI practices, but not all--only those
for which ANSI C *requires* a diagnostic.
A feature to report any failure to conform to ANSI C might be
useful in some instances, but would require considerable
additional work and would be quite different from `-pedantic'. We
don't have plans to support such a feature in the near future.
`-pedantic-errors'
Like `-pedantic', except that errors are produced rather than
warnings.
`-w'
Inhibit all warning messages.
`-Wno-import'
Inhibit warning messages about the use of `#import'.
`-Wchar-subscripts'
Warn if an array subscript has type `char'. This is a common cause
of error, as programmers often forget that this type is signed on
some machines.
`-Wcomment'
Warn whenever a comment-start sequence `/*' appears in a `/*'
comment, or whenever a Backslash-Newline appears in a `//' comment.
`-Wformat'
Check calls to `printf' and `scanf', etc., to make sure that the
arguments supplied have types appropriate to the format string
specified.
`-Wimplicit-int'
Warn when a declaration does not specify a type.
`-Wimplicit-function-declaration'
`-Werror-implicit-function-declaration'
Give a warning (or error) whenever a function is used before being
declared.
`-Wimplicit'
Same as `-Wimplicit-int' and `-Wimplicit-function-'
`declaration'.
`-Wmain'
Warn if the type of `main' is suspicious. `main' should be a
function with external linkage, returning int, taking either zero
arguments, two, or three arguments of appropriate types.
`-Wmultichar'
Warn if a multicharacter constant (`'FOOF'') is used. Usually they
indicate a typo in the user's code, as they have
implementation-defined values, and should not be used in portable
code.
`-Wparentheses'
Warn if parentheses are omitted in certain contexts, such as when
there is an assignment in a context where a truth value is
expected, or when operators are nested whose precedence people
often get confused about.
Also warn about constructions where there may be confusion to which
`if' statement an `else' branch belongs. Here is an example of
such a case:
{
if (a)
if (b)
foo ();
else
bar ();
}
In C, every `else' branch belongs to the innermost possible `if'
statement, which in this example is `if (b)'. This is often not
what the programmer expected, as illustrated in the above example
by indentation the programmer chose. When there is the potential
for this confusion, GNU C will issue a warning when this flag is
specified. To eliminate the warning, add explicit braces around
the innermost `if' statement so there is no way the `else' could
belong to the enclosing `if'. The resulting code would look like
this:
{
if (a)
{
if (b)
foo ();
else
bar ();
}
}
`-Wreturn-type'
Warn whenever a function is defined with a return-type that
defaults to `int'. Also warn about any `return' statement with no
return-value in a function whose return-type is not `void'.
`-Wswitch'
Warn whenever a `switch' statement has an index of enumeral type
and lacks a `case' for one or more of the named codes of that
enumeration. (The presence of a `default' label prevents this
warning.) `case' labels outside the enumeration range also
provoke warnings when this option is used.
`-Wtrigraphs'
Warn if any trigraphs are encountered (assuming they are enabled).
`-Wunused'
Warn whenever a variable is unused aside from its declaration,
whenever a function is declared static but never defined, whenever
a label is declared but not used, and whenever a statement
computes a result that is explicitly not used.
In order to get a warning about an unused function parameter, you
must specify both `-W' and `-Wunused'.
To suppress this warning for an expression, simply cast it to
void. For unused variables, parameters and labels, use the
`unused' attribute (*note Variable Attributes::.).
`-Wuninitialized'
An automatic variable is used without first being initialized.
These warnings are possible only in optimizing compilation,
because they require data flow information that is computed only
when optimizing. If you don't specify `-O', you simply won't get
these warnings.
These warnings occur only for variables that are candidates for
register allocation. Therefore, they do not occur for a variable
that is declared `volatile', or whose address is taken, or whose
size is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
structures, unions or arrays, even when they are in registers.
Note that there may be no warning about a variable that is used
only to compute a value that itself is never used, because such
computations may be deleted by data flow analysis before the
warnings are printed.
These warnings are made optional because GCC is not smart enough
to see all the reasons why the code might be correct despite
appearing to have an error. Here is one example of how this can
happen:
{
int x;
switch (y)
{
case 1: x = 1;
break;
case 2: x = 4;
break;
case 3: x = 5;
}
foo (x);
}
If the value of `y' is always 1, 2 or 3, then `x' is always
initialized, but GCC doesn't know this. Here is another common
case:
{
int save_y;
if (change_y) save_y = y, y = new_y;
...
if (change_y) y = save_y;
}
This has no bug because `save_y' is used only if it is set.
Some spurious warnings can be avoided if you declare all the
functions you use that never return as `noreturn'. *Note Function
Attributes::.
`-Wunknown-pragmas'
Warn when a #pragma directive is encountered which is not
understood by GCC. If this command line option is used, warnings
will even be issued for unknown pragmas in system header files.
This is not the case if the warnings were only enabled by the
`-Wall' command line option.
`-Wall'
All of the above `-W' options combined. This enables all the
warnings about constructions that some users consider
questionable, and that are easy to avoid (or modify to prevent the
warning), even in conjunction with macros.
The following `-W...' options are not implied by `-Wall'. Some of
them warn about constructions that users generally do not consider
questionable, but which occasionally you might wish to check for;
others warn about constructions that are necessary or hard to avoid in
some cases, and there is no simple way to modify the code to suppress
the warning.
`-W'
Print extra warning messages for these events:
* A nonvolatile automatic variable might be changed by a call to
`longjmp'. These warnings as well are possible only in
optimizing compilation.
The compiler sees only the calls to `setjmp'. It cannot know
where `longjmp' will be called; in fact, a signal handler
could call it at any point in the code. As a result, you may
get a warning even when there is in fact no problem because
`longjmp' cannot in fact be called at the place which would
cause a problem.
* A function can return either with or without a value.
(Falling off the end of the function body is considered
returning without a value.) For example, this function would
evoke such a warning:
foo (a)
{
if (a > 0)
return a;
}
* An expression-statement or the left-hand side of a comma
expression contains no side effects. To suppress the
warning, cast the unused expression to void. For example, an
expression such as `x[i,j]' will cause a warning, but
`x[(void)i,j]' will not.
* An unsigned value is compared against zero with `<' or `<='.
* A comparison like `x<=y<=z' appears; this is equivalent to
`(x<=y ? 1 : 0) <= z', which is a different interpretation
from that of ordinary mathematical notation.
* Storage-class specifiers like `static' are not the first
things in a declaration. According to the C Standard, this
usage is obsolescent.
* If `-Wall' or `-Wunused' is also specified, warn about unused
arguments.
* A comparison between signed and unsigned values could produce
an incorrect result when the signed value is converted to
unsigned. (But don't warn if `-Wno-sign-compare' is also
specified.)
* An aggregate has a partly bracketed initializer. For
example, the following code would evoke such a warning,
because braces are missing around the initializer for `x.h':
struct s { int f, g; };
struct t { struct s h; int i; };
struct t x = { 1, 2, 3 };
* An aggregate has an initializer which does not initialize all
members. For example, the following code would cause such a
warning, because `x.h' would be implicitly initialized to
zero:
struct s { int f, g, h; };
struct s x = { 3, 4 };
`-Wtraditional'
Warn about certain constructs that behave differently in
traditional and ANSI C.
* Macro arguments occurring within string constants in the
macro body. These would substitute the argument in
traditional C, but are part of the constant in ANSI C.
* A function declared external in one block and then used after
the end of the block.
* A `switch' statement has an operand of type `long'.
* A non-`static' function declaration follows a `static' one.
This construct is not accepted by some traditional C
compilers.
`-Wundef'
Warn if an undefined identifier is evaluated in an `#if' directive.
`-Wshadow'
Warn whenever a local variable shadows another local variable.
`-Wid-clash-LEN'
Warn whenever two distinct identifiers match in the first LEN
characters. This may help you prepare a program that will compile
with certain obsolete, brain-damaged compilers.
`-Wlarger-than-LEN'
Warn whenever an object of larger than LEN bytes is defined.
`-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.
`-Wbad-function-cast'
Warn whenever a function call is cast to a non-matching type. For
example, warn if `int malloc()' is cast to `anything *'.
`-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 *'.
`-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.
`-Wwrite-strings'
Give string constants the type `const char[LENGTH]' so that
copying the address of one into a non-`const' `char *' pointer
will get a warning. These warnings will help you find at compile
time code that can try to write into a string constant, but only
if you have been very careful about using `const' in declarations
and prototypes. Otherwise, it will just be a nuisance; this is
why we did not make `-Wall' request these warnings.
`-Wconversion'
Warn if a prototype causes a type conversion that is different
from what would happen to the same argument in the absence of a
prototype. This includes conversions of fixed point to floating
and vice versa, and conversions changing the width or signedness
of a fixed point argument except when the same as the default
promotion.
Also, warn if a negative integer constant expression is implicitly
converted to an unsigned type. For example, warn about the
assignment `x = -1' if `x' is unsigned. But do not warn about
explicit casts like `(unsigned) -1'.
`-Wsign-compare'
Warn when a comparison between signed and unsigned values could
produce an incorrect result when the signed value is converted to
unsigned. This warning is also enabled by `-W'; to get the other
warnings of `-W' without this warning, use `-W -Wno-sign-compare'.
`-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.)
`-Wstrict-prototypes'
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 which specifies the
argument types.)
`-Wmissing-prototypes'
Warn if a global function is defined without a previous prototype
declaration. This warning is issued even if the definition itself
provides a prototype. The aim is to detect global functions that
fail to be declared in header files.
`-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-noreturn'
Warn about functions which might be candidates for attribute
`noreturn'. Note these are only possible candidates, not absolute
ones. Care should be taken to manually verify functions actually
do not ever return before adding the `noreturn' attribute,
otherwise subtle code generation bugs could be introduced.
`-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.
`-Wnested-externs'
Warn if an `extern' declaration is encountered within an function.
`-Winline'
Warn if a function can not be inlined, and either it was declared
as inline, or else the `-finline-functions' option was given.
`-Wlong-long'
Warn if `long long' type is used. This is default. To inhibit
the warning messages, use `-Wno-long-long'. Flags `-Wlong-long'
and `-Wno-long-long' are taken into account only when `-pedantic'
flag is used.
`-Werror'
Make all warnings into errors.