## Compiling C++ Programs

C++ source files conventionally use one of the suffixes .C, .cc, .cpp, .CPP, .c++, .cp, or .cxx; C++ header files often use .hh or .H; and preprocessed C++ files use the suffix .ii. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name gcc).

However, C++ programs often require class libraries as well as a compiler that understands the C++ language---and under some circumstances, you might want to compile programs or header files from standard input, or otherwise without a suffix that flags them as C++ programs. You might also like to precompile a C header file with a .h extension to be used in C++ compilations. g++ is a program that calls GCC with the default language set to C++, and automatically specifies linking against the C++ library. On many systems, g++ is also installed with the name c++.

When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs.

## Options Controlling C Dialect

The following options control the dialect of C (or languages derived from C, such as C++ and Objective-C) that the compiler accepts:

-ansi
  In C mode, support all ISO C90 programs. In C++ mode, remove GNU extensions that conflict with ISO C++.

  This turns off certain features of GCC that are incompatible with ISO C90 (when compiling C code), or of standard C++ (when compiling C++ code), such as the `"asm"` and `"typeof"` keywords, and predefined macros such as `"unix"` and `"vax"` that identify the type of system you are using. It also enables the undesirable and rarely used ISO trigraph feature. For the C compiler, it disables recognition of C++ style // comments as well as the `"inline"` keyword.

  The alternate keywords `"__asm__"`, `"__extension__"`, `"__inline__"` and `"__typeof__"` continue to work despite -ansi. You would not want to use them in an ISO C program, of course, but it is useful to put them in header files that might be included in compilations done with -ansi. Alternate predefined macros such as `"__unix__"` and `"__vax__"` are also available, with or without -ansi.

  The -ansi option does not cause non-ISO programs to be rejected gratuitously. For that, -pedantic is required in addition to -ansi.

  The macro `"__STRICT_ANSI__"` is predefined when the -ansi option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the ISO standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things.

  Functions which would normally be built in but do not have semantics defined by ISO C (such as `"alloca"` and `"ffs"`) are not built-in functions with -ansi is used.

-std=
  Determine the language standard. This option is currently only supported when compiling C or C++. A value for this option must be provided; possible values are
    c89
    iso9899:1990
      ISO C90 (same as -ansi).
    iso9899:199409
      ISO C90 as modified in amendment 1.
    c99
    c9x
    iso9899:1999
    iso9899:199x
      ISO C99. Note that this standard is not yet fully supported; see <http://gcc.gnu.org/gcc-3.4/c99status.html> for more information. The names c9x and iso9899:199x are deprecated.
    gnu89
      Default, ISO C90 plus GNU extensions (including some C99 features).
    gnu99
    gnu9x
      ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC, this will become the default. The name gnu9x is deprecated.
    c++98
      The 1998 ISO C++ standard plus amendments.
    gnu++98
      The same as -std=c++98 plus GNU extensions. This is the default for C++ code.

    Even when this option is not specified, you can still use some of the features of newer standards in so far as they do not conflict with previous C standards. For example, you may use `"__restrict__"` even when -std=c99 is not specified.

    The -std options specifying some version of ISO C have the same effects as -ansi, except that features that were not in ISO C90 but are in the specified version (for example, // comments and the `"inline"` keyword in ISO C99) are not disabled.

-aux-info filename
  Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C.

  Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (I, N for new or O for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (C or F, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration.

-fno-asm
  Do not recognize `"asm"`, `"inline"` or `"typeof"` as a keyword, so that code can use these words as identifiers. You can use the keywords `"__asm__"`, `"__inline__"` and `"__typeof__"` instead. -ansi implies -fno-asm.

  In C++, this switch only affects the `"typeof"` keyword, since `"asm"` and `"inline"` are standard keywords. You may want to use the -fno-gnu-keywords flag instead, which has the same effect. In C99 mode (-std=c99 or -std=gnu99), this switch only affects the `"asm"` and `"typeof"` keywords, since `"inline"` is a standard keyword in ISO C99.

-fno-builtin
-fno-builtin-function
  Don't recognize built-in functions that do not begin with __builtin_ as prefix.

  GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to `"alloca"` may become single instructions that adjust the stack directly, and calls to `"memcpy"` may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library.

  With the -fno-builtin-function option only the built-in function function is disabled. function must not begin with __builtin_. If a function is named this is not built-in in this version of GCC, this option is ignored. There is no corresponding -fbuiltin-function option; if you wish to enable built-in functions selectively when using -fno-builtin or -ffreestanding, you may define macros such as:

              #define abs(n)          __builtin_abs ((n))
              #define strcpy(d, s)    __builtin_strcpy ((d), (s))

-fhosted
  Assert that compilation takes place in a hosted environment. This implies -fbuiltin. A hosted environment is one in which the entire standard library is available, and in which `"main"` has a return type of `"int"`. Examples are nearly everything except a kernel. This is equivalent to -fno-freestanding.
-ffreestanding
  Assert that compilation takes place in a freestanding environment. This implies -fno-builtin. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at `"main"`. The most obvious example is an OS kernel. This is equivalent to -fno-hosted.
-fms-extensions
  Accept some non-standard constructs used in Microsoft header files.
-trigraphs
  Support ISO C trigraphs. The -ansi option (and -std options for strict ISO C conformance) implies -trigraphs.
-no-integrated-cpp
  Performs a compilation in two passes: preprocessing and compiling. This option allows a user supplied ``cc1'', ``cc1plus'', or ``cc1obj'' via the -B option. The user supplied compilation step can then add in an additional preprocessing step after normal preprocessing but before compiling. The default is to use the integrated cpp (internal cpp)

  The semantics of this option will change if ``cc1'', ``cc1plus'', and ``cc1obj'' are merged.

-traditional
-traditional-cpp
  Formerly, these options caused GCC to attempt to emulate a pre-standard C compiler. They are now only supported with the -E switch. The preprocessor continues to support a pre-standard mode. See the GNU CPP manual for details.
-fcond-mismatch
  Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. This option is not supported for C++.
-funsigned-char
  Let the type `"char"` be unsigned, like `"unsigned char"`.

  Each kind of machine has a default for what `"char"` should be. It is either like `"unsigned char"` by default or like `"signed char"` by default.

  Ideally, a portable program should always use `"signed char"` or `"unsigned char"` when it depends on the signedness of an object. But many programs have been written to use plain `"char"` and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default.

  The type `"char"` is always a distinct type from each of `"signed char"` or `"unsigned char"`, even though its behavior is always just like one of those two.

-fsigned-char
  Let the type `"char"` be signed, like `"signed char"`.

  Note that this is equivalent to -fno-unsigned-char, which is the negative form of -funsigned-char. Likewise, the option -fno-signed-char is equivalent to -funsigned-char.

-fsigned-bitfields
-funsigned-bitfields
-fno-signed-bitfields
-fno-unsigned-bitfields
  These options control whether a bit-field is signed or unsigned, when the declaration does not use either `"signed"` or `"unsigned"`. By default, such a bit-field is signed, because this is consistent: the basic integer types such as `"int"` are signed types.
-fwritable-strings
  Store string constants in the writable data segment and don't uniquize them. This is for compatibility with old programs which assume they can write into string constants.

  Writing into string constants is a very bad idea; ``constants'' should be constant.

  This option is deprecated.

## 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:

-fabi-version=n
  Use version n of the C++ ABI. Version 2 is the version of the C++ ABI that first appeared in G++ 3.4. Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. Version 0 will always be the version that conforms most closely to the C++ ABI specification. Therefore, the ABI obtained using version 0 will change as ABI bugs are fixed.

  The default is version 2.

-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. This check is normally unnecessary because the C++ standard specifies that `"operator new"` will only return `0` if it is declared throw(), in which case the compiler will always check the return value even without this option. In all other cases, when `"operator new"` has a non-empty exception specification, memory exhaustion is signalled by throwing `"std::bad_alloc"`. 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.

-fno-const-strings
  Give string constants type `"char *"` instead of type `"const char *"`. By default, G++ uses type `"const char *"` as required by the standard. Even if you use -fno-const-strings, you cannot actually modify the value of a string constant, unless you also use -fwritable-strings.

  This option might be removed in a future release of G++. For maximum portability, you should structure your code so that it works with string constants that have type `"const char *"`.

-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.
-fno-enforce-eh-specs
  Don't check for violation of exception specifications at runtime. This option violates the C++ standard, but may be useful for reducing code size in production builds, much like defining NDEBUG. The compiler will still optimize based on the exception specifications.
-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 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 G++, 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 `"typeof"` as a keyword, so that code can use this word as an identifier. You can use the keyword `"__typeof__"` instead. -ansi implies -fno-gnu-keywords.
-fno-implicit-templates
  Never emit code for non-inline templates which are instantiated implicitly (i.e. by use); only emit code for explicit instantiations.
-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.
-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.
-fms-extensions
  Disable pedantic warnings about constructs used in MFC, such as implicit int and getting a pointer to member function via non-standard syntax.
-fno-nonansi-builtins
  Disable built-in declarations of functions that are not mandated by ANSI/ISO C. These include `"ffs"`, `"alloca"`, `"_exit"`, `"index"`, `"bzero"`, `"conjf"`, and other related functions.
-fno-operator-names
  Do not treat the operator name keywords `"and"`, `"bitand"`, `"bitor"`, `"compl"`, `"not"`, `"or"` and `"xor"` as synonyms as keywords.
-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 some diagnostics about nonconformant code from errors to warnings. Thus, using -fpermissive will allow some nonconforming code to compile.
-frepo
  Enable automatic template instantiation at link time. This option also implies -fno-implicit-templates.
-fno-rtti
  Disable generation of information about every class with virtual functions for use by the C++ runtime type identification features (dynamic_cast and typeid). If you don't use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but it will generate it as needed.
-fstats
  Emit statistics about front-end processing at the end of the compilation. This information is generally only useful to the G++ development team.
-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.
-fuse-cxa-atexit
  Register destructors for objects with static storage duration with the `"__cxa_atexit"` function rather than the `"atexit"` function. This option is required for fully standards-compliant handling of static destructors, but will only work if your C library supports `"__cxa_atexit"`.
-fno-weak
  Do not use weak symbol support, even if it is provided by the linker. By default, G++ will use weak symbols if they are available. This option exists only for testing, and should not be used by end-users; it will result in inferior code and has no benefits. This option may be removed in a future release of G++.
-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 that these functions will have linkage like inline functions; they just won't be inlined by default.
-Wabi (C++ only)
  Warn when G++ generates code that is probably not compatible with the vendor-neutral C++ ABI. Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be cases where warnings are emitted even though the code that is generated will be compatible.

  You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers.

  The known incompatibilities at this point include:

    *
      Incorrect handling of tail-padding for bit-fields. G++ may attempt to pack data into the same byte as a base class. For example:

                  struct A { virtual void f(); int f1 : 1; };
                  struct B : public A { int f2 : 1; };

      In this case, G++ will place `"B::f2"` into the same byte as`"A::f1"`; other compilers will not. You can avoid this problem by explicitly padding `"A"` so that its size is a multiple of the byte size on your platform; that will cause G++ and other compilers to layout `"B"` identically.

    *
      Incorrect handling of tail-padding for virtual bases. G++ does not use tail padding when laying out virtual bases. For example:

                  struct A { virtual void f(); char c1; };
                  struct B { B(); char c2; };
                  struct C : public A, public virtual B {};

      In this case, G++ will not place `"B"` into the tail-padding for `"A"`; other compilers will. You can avoid this problem by explicitly padding `"A"` so that its size is a multiple of its alignment (ignoring virtual base classes); that will cause G++ and other compilers to layout `"C"` identically.

    *
      Incorrect handling of bit-fields with declared widths greater than that of their underlying types, when the bit-fields appear in a union. For example:

                  union U { int i : 4096; };

      Assuming that an `"int"` does not have 4096 bits, G++ will make the union too small by the number of bits in an `"int"`.

    *
      Empty classes can be placed at incorrect offsets. For example:

                  struct A {};

                  struct B {
                    A a;
                    virtual void f ();
                  };

                  struct C : public B, public A {};

      G++ will place the `"A"` base class of `"C"` at a nonzero offset; it should be placed at offset zero. G++ mistakenly believes that the `"A"` data member of `"B"` is already at offset zero.

    *
      Names of template functions whose types involve `"typename"` or template template parameters can be mangled incorrectly.

                  template <typename Q>
                  void f(typename Q::X) {}

                  template <template <typename> class Q>
                  void f(typename Q<int>::X) {}

      Instantiations of these templates may be mangled incorrectly.

-Wctor-dtor-privacy (C++ only)
  Warn when a class seems unusable because all the constructors or destructors in that class are private, and it has neither friends nor public static member functions.
-Wnon-virtual-dtor (C++ only)
  Warn when a class appears to be polymorphic, thereby requiring a virtual destructor, yet it declares a non-virtual one. This warning is enabled by -Wall.
-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) { }
              };

  The compiler will rearrange the member initializers for i and j to match the declaration order of the members, emitting a warning to that effect. This warning is enabled by -Wall.

The following -W... options are not affected by -Wall.

-Weffc++ (C++ only)
  Warn about violations of the following style guidelines from Scott Meyers' Effective C++ book:
    *
      Item 11: Define a copy constructor and an assignment operator for classes with dynamically allocated memory.
    *
      Item 12: Prefer initialization to assignment in constructors.
    *
      Item 14: Make destructors virtual in base classes.
    *
      Item 15: Have `"operator="` return a reference to `*this`.
    *
      Item 23: Don't try to return a reference when you must return an object.

    Also warn about violations of the following style guidelines from Scott Meyers' More Effective C++ book:

    *
      Item 6: Distinguish between prefix and postfix forms of increment and decrement operators.
    *
      Item 7: Never overload `"&&"`, `"||"`, or `","`.

    When selecting this option, be aware that the standard library headers do not obey all of these guidelines; use grep -v to filter out those warnings.

-Wno-deprecated (C++ only)
  Do not warn about usage of deprecated features.
-Wno-non-template-friend (C++ only)
  Disable warnings when non-templatized friend functions are declared within a template. Since the advent of explicit template specification support in G++, if the name of the friend is an unqualified-id (i.e., 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 be turned off 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 to a non-void type is used within a C++ program. The new-style casts (static_cast, reinterpret_cast, and const_cast) are less vulnerable to unintended effects and much easier to search for.
-Woverloaded-virtual (C++ only)
  Warn when a function declaration hides virtual functions from a base class. For example, in:

              struct A {
                virtual void f();
              };

              struct B: public A {
                void f(int);
              };

  the `"A"` class version of `"f"` is hidden in `"B"`, and code like:

              B* b;
              b->f();

  will fail to compile.

-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 enumerated 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.

              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 =.

## Options Controlling Objective-C Dialect

(NOTE: This manual does not describe the Objective-C language itself. See <http://gcc.gnu.org/readings.html> for references.)

This section describes the command-line options that are only meaningful for Objective-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 `"some_class.m"` like this:

            gcc -g -fgnu-runtime -O -c some_class.m

In this example, -fgnu-runtime is an option meant only for Objective-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 Objective-C programs:

-fconstant-string-class=class-name
  Use class-name as the name of the class to instantiate for each literal string specified with the syntax `"@"...""`. The default class name is `"NXConstantString"` if the GNU runtime is being used, and `"NSConstantString"` if the NeXT runtime is being used (see below). The -fconstant-cfstrings option, if also present, will override the -fconstant-string-class setting and cause `"@"...""` literals to be laid out as constant CoreFoundation strings.
-fgnu-runtime
  Generate object code compatible with the standard GNU Objective-C runtime. This is the default for most types of systems.
-fnext-runtime
  Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac OS X. The macro `"__NEXT_RUNTIME__"` is predefined if (and only if) this option is used.
-fno-nil-receivers
  Assume that all Objective-C message dispatches (e.g., `"[receiver message:arg]"`) in this translation unit ensure that the receiver is not `"nil"`. This allows for more efficient entry points in the runtime to be used. Currently, this option is only available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
-fobjc-exceptions
  Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by C++ and Java. Currently, this option is only available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.

                @try {
                  ...
                     @throw expr;
                  ...
                }
                @catch (AnObjCClass *exc) {
                  ...
                    @throw expr;
                  ...
                    @throw;
                  ...
                }
                @catch (AnotherClass *exc) {
                  ...
                }
                @catch (id allOthers) {
                  ...
                }
                @finally {
                  ...
                    @throw expr;
                  ...
                }

  The `@throw` statement may appear anywhere in an Objective-C or Objective-C++ program; when used inside of a `@catch` block, the `@throw` may appear without an argument (as shown above), in which case the object caught by the `@catch` will be rethrown.

  Note that only (pointers to) Objective-C objects may be thrown and caught using this scheme. When an object is thrown, it will be caught by the nearest `@catch` clause capable of handling objects of that type, analogously to how `"catch"` blocks work in C++ and Java. A `"@catch(id ...)"` clause (as shown above) may also be provided to catch any and all Objective-C exceptions not caught by previous `@catch` clauses (if any).

  The `@finally` clause, if present, will be executed upon exit from the immediately preceding `"@try ... @catch"` section. This will happen regardless of whether any exceptions are thrown, caught or rethrown inside the `"@try ... @catch"` section, analogously to the behavior of the `"finally"` clause in Java.

  There are several caveats to using the new exception mechanism:

    *
      Although currently designed to be binary compatible with `"NS_HANDLER"`-style idioms provided by the `"NSException"` class, the new exceptions can only be used on Mac OS X 10.3 (Panther) and later systems, due to additional functionality needed in the (NeXT) Objective-C runtime.
    *
      As mentioned above, the new exceptions do not support handling types other than Objective-C objects. Furthermore, when used from Objective-C++, the Objective-C exception model does not interoperate with C++ exceptions at this time. This means you cannot `@throw` an exception from Objective-C and `"catch"` it in C++, or vice versa (i.e., `"throw ... @catch"`).

    The -fobjc-exceptions switch also enables the use of synchronization blocks for thread-safe execution:

                  @synchronized (ObjCClass *guard) {
                    ...
                  }

    Upon entering the `@synchronized` block, a thread of execution shall first check whether a lock has been placed on the corresponding `"guard"` object by another thread. If it has, the current thread shall wait until the other thread relinquishes its lock. Once `"guard"` becomes available, the current thread will place its own lock on it, execute the code contained in the `@synchronized` block, and finally relinquish the lock (thereby making `"guard"` available to other threads).

    Unlike Java, Objective-C does not allow for entire methods to be marked `@synchronized`. Note that throwing exceptions out of `@synchronized` blocks is allowed, and will cause the guarding object to be unlocked properly.

-freplace-objc-classes
  Emit a special marker instructing ld(1) not to statically link in the resulting object file, and allow dyld(1) to load it in at run time instead. This is used in conjunction with the Fix-and-Continue debugging mode, where the object file in question may be recompiled and dynamically reloaded in the course of program execution, without the need to restart the program itself. Currently, Fix-and-Continue functionality is only available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
-fzero-link
  When compiling for the NeXT runtime, the compiler ordinarily replaces calls to `"objc_getClass("...")"` (when the name of the class is known at compile time) with static class references that get initialized at load time, which improves run-time performance. Specifying the -fzero-link flag suppresses this behavior and causes calls to `"objc_getClass("...")"` to be retained. This is useful in Zero-Link debugging mode, since it allows for individual class implementations to be modified during program execution.
-gen-decls
  Dump interface declarations for all classes seen in the source file to a file named sourcename.decl.
-Wno-protocol
  If a class is declared to implement a protocol, a warning is issued for every method in the protocol that is not implemented by the class. The default behavior is to issue a warning for every method not explicitly implemented in the class, even if a method implementation is inherited from the superclass. If you use the `"-Wno-protocol"` option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them.
-Wselector
  Warn if multiple methods of different types for the same selector are found during compilation. The check is performed on the list of methods in the final stage of compilation. Additionally, a check is performed for each selector appearing in a `"@selector(...)"` expression, and a corresponding method for that selector has been found during compilation. Because these checks scan the method table only at the end of compilation, these warnings are not produced if the final stage of compilation is not reached, for example because an error is found during compilation, or because the `"-fsyntax-only"` option is being used.
-Wundeclared-selector
  Warn if a `"@selector(...)"` expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the `"@selector(...)"` expression, either explicitly in an `@interface` or `@protocol` declaration, or implicitly in an `@implementation` section. This option always performs its checks as soon as a `"@selector(...)"` expression is found, while `"-Wselector"` only performs its checks in the final stage of compilation. This also enforces the coding style convention that methods and selectors must be declared before being used.
-print-objc-runtime-info
  Generate C header describing the largest structure that is passed by value, if any.