7 Extensions to the C++ Language

The GNU compiler provides these extensions to the C++ language (and you can also use most of the C language extensions in your C++ programs). If you want to write code that checks whether these features are available, you can test for the GNU compiler the same way as for C programs: check for a predefined macro __GNUC__. You can also use __GNUG__ to test specifically for GNU C++ (see Predefined Macros).

• C++ Volatiles: What constitutes an access to a volatile object.
• Restricted Pointers: C99 restricted pointers and references.
• Vague Linkage: Where G++ puts inlines, vtables and such.
• C++ Interface: You can use a single C++ header file for both declarations and definitions.
• Template Instantiation: Methods for ensuring that exactly one copy of each needed template instantiation is emitted.
• Bound member functions: You can extract a function pointer to the method denoted by a ‘->*’ or ‘.*’ expression.
• C++ Attributes: Variable, function, and type attributes for C++ only.
• Function Multiversioning: Declaring multiple function versions.
• Namespace Association: Strong using-directives for namespace association.
• Type Traits: Compiler support for type traits
• Java Exceptions: Tweaking exception handling to work with Java.
• Deprecated Features: Things will disappear from G++.
• Backwards Compatibility: Compatibilities with earlier definitions of C++.