(NOTE: This manual does not describe the Objective-C and Objective-C++ languages themselves. See Language Standards Supported by GCC, for references.)
This section describes the command-line options that are only meaningful for Objective-C and Objective-C++ programs. You can also use most of the language-independent GNU compiler options. 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 and Objective-C++ programs; you can use the other options with any language supported by GCC.
Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front-end (e.g., -Wtraditional
). Similarly, Objective-C++ compilations may use C++-specific options (e.g., -Wabi
).
Here is a list of options that are only for compiling Objective-C and Objective-C++ programs:
-fconstant-string-class=
class-name
@"..."
. 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, overrides the -fconstant-string-class
setting and cause @"..."
literals to be laid out as constant CoreFoundation strings. -fgnu-runtime
-fnext-runtime
__NEXT_RUNTIME__
is predefined if (and only if) this option is used. -fno-nil-receivers
[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. This option is only available in conjunction with the NeXT runtime and ABI version 0 or 1. -fobjc-abi-version=
n
-fobjc-call-cxx-cdtors
- (id) .cxx_construct
instance method which runs non-trivial default constructors on any such instance variables, in order, and then return self
. Similarly, check if any instance variable is a C++ object with a non-trivial destructor, and if so, synthesize a special - (void) .cxx_destruct
method which runs all such default destructors, in reverse order. The - (id) .cxx_construct
and - (void) .cxx_destruct
methods thusly generated only operate on instance variables declared in the current Objective-C class, and not those inherited from superclasses. It is the responsibility of the Objective-C runtime to invoke all such methods in an object's inheritance hierarchy. The - (id) .cxx_construct
methods are invoked by the runtime immediately after a new object instance is allocated; the - (void) .cxx_destruct
methods are invoked immediately before the runtime deallocates an object instance.
As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has support for invoking the - (id) .cxx_construct
and - (void) .cxx_destruct
methods.
-fobjc-direct-dispatch
-fobjc-exceptions
@try
, @throw
, @catch
, @finally
and @synchronized
. This option is available with both the GNU runtime and the NeXT runtime (but not available in conjunction with the NeXT runtime on Mac OS X 10.2 and earlier). -fobjc-gc
-fobjc-nilcheck
-fno-objc-nilcheck
. Class methods and super calls are never checked for nil in this way no matter what this flag is set to. Currently this flag does nothing when the GNU runtime, or an older version of the NeXT runtime ABI, is used. -fobjc-std=objc1
-freplace-objc-classes
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
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. The GNU runtime currently always retains calls to objc_get_class("...")
regardless of command-line options. -fno-local-ivars
-fno-local-ivars
flag disables this behavior thus avoiding variable shadowing issues. -fivar-visibility=
[public
|protected
|private
|package
]
-gen-decls
-Wassign-intercept
(Objective-C and Objective-C++ only)
-Wno-protocol
(Objective-C and Objective-C++ only)
-Wno-protocol
option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them. -Wselector
(Objective-C and Objective-C++ only)
@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. -Wstrict-selector-match
(Objective-C and Objective-C++ only)
id
or Class
. When this flag is off (which is the default behavior), the compiler omits such warnings if any differences found are confined to types that share the same size and alignment. -Wundeclared-selector
(Objective-C and Objective-C++ only)
@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
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Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gcc/Objective_002dC-and-Objective_002dC_002b_002b-Dialect-Options.html