Extensions to ANSI-/ISO-C++

The extensions described below are accepted in the C++ 2017 and C++ 2020 language modes, except when the option -R strict_errors or ANSI-VIOLATIONS=*ERROR has been set in strict mode. Note that all extensions to ANSI/ISO C (see section “Extensions to ANSI/ISO C”) are also supported in the C++ modes.

• A qualified name may be used in the declaration of a class member:

  struct A {
     int A::f(); // ANSI requires int f();
  };
  

• In extended C++ 2017 mode and in extended C++ 2020 mode an implicit conversion between functions with "C" und "C++" linkage exists:

  extern "C" void f();
  void (*pf)() = &f;

• In extended C++ 2017 mode and in extended C++ 2020 mode an implicit conversion from string literals to the type char* exists (in C++ 2017 string literals are of type const char *):

  char *p1 = "abc";
  char *p2 = x ? "abc" : "def";

• The preprocessor macro c_plusplus is defined in addition to the standard-compliant macro __cplusplus. No warning is issued.