Objective-C and Objective-C++ Languages#
GCC supports ‘traditional’ Objective-C (also known as ‘Objective-C 1.0’) and contains support for the Objective-C exception and synchronization syntax. It has also support for a number of ‘Objective-C 2.0’ language extensions, including properties, fast enumeration (only for Objective-C), method attributes and the @optional and @required keywords in protocols. GCC supports Objective-C++ and features available in Objective-C are also available in Objective-C++.
GCC by default uses the GNU Objective-C runtime library, which is part
of GCC and is not the same as the Apple/NeXT Objective-C runtime
library used on Apple systems. There are a number of differences
documented in this manual. The options -fgnu-runtime and
-fnext-runtime allow you to switch between producing output
that works with the GNU Objective-C runtime library and output that
works with the Apple/NeXT Objective-C runtime library.
There is no formal written standard for Objective-C or Objective-C++. The authoritative manual on traditional Objective-C (1.0) is ‘Object-Oriented Programming and the Objective-C Language’: http://www.gnustep.org/resources/documentation/ObjectivCBook.pdf is the original NeXTstep document.
The Objective-C exception and synchronization syntax (that is, the
keywords @try, @throw, @catch,
@finally and @synchronized) is
supported by GCC and is enabled with the option
-fobjc-exceptions. The syntax is briefly documented in this
manual and in the Objective-C 2.0 manuals from Apple.
The Objective-C 2.0 language extensions and features are automatically
enabled; they include properties (via the @property,
@synthesize and
@dynamic keywords), fast enumeration (not available in
Objective-C++), attributes for methods (such as deprecated,
noreturn, sentinel, format),
the unused attribute for method arguments, the
@package keyword for instance variables and the @optional and
@required keywords in protocols. You can disable all these
Objective-C 2.0 language extensions with the option
-fobjc-std=objc1, which causes the compiler to recognize the
same Objective-C language syntax recognized by GCC 4.0, and to produce
an error if one of the new features is used.
GCC has currently no support for non-fragile instance variables.
The authoritative manual on Objective-C 2.0 is available from Apple:
For more information concerning the history of Objective-C that is available online, see https://gcc.gnu.org/readings.html