In the past, the GNU C++ compiler was extended to experiment with new features, at a time when the C++ language was still evolving. Now that the C++ standard is complete, some of those features are superseded by superior alternatives. Using the old features might cause a warning in some cases that the feature will be dropped in the future. In other cases, the feature might be gone already.
While the list below is not exhaustive, it documents some of the options that are now deprecated or have been removed:
-fno-for-scope-ffriend-injectionG++ allows a virtual function returning ‘void *’ to be overridden by one returning a different pointer type. This extension to the covariant return type rules is now deprecated and will be removed from a future version.
The use of default arguments in function pointers, function typedefs and other places where they are not permitted by the standard is deprecated and will be removed from a future version of G++.
G++ allows floating-point literals to appear in integral constant expressions, e.g. ‘ enum E { e = int(2.2 * 3.7) } ’ This extension is deprecated and will be removed from a future version.
G++ allows static data members of const floating-point type to be declared with an initializer in a class definition. The standard only allows initializers for static members of const integral types and const enumeration types so this extension has been deprecated and will be removed from a future version.
G++ allows attributes to follow a parenthesized direct initializer, e.g. ‘ int f (0) __attribute__ ((something)); ’ This extension has been ignored since G++ 3.3 and is deprecated.
G++ allows anonymous structs and unions to have members that are not public non-static data members (i.e. fields). These extensions are deprecated.