C Reference Manual Reading Notes: 007 C++ Compatibility

1. Character Sets

    The token respelling and trigraphs in Standard C are part of the C++ Standard, but they are not common in pre-Standard C++ implementations. Boths C and C++ allow universal character names with same syntax, but only C explicitly allows other implementation-defined character in identifiers. (One expects that C++ implementations will provide them as an extension.)

 

2. Comments

    C99 comments are acceptable as C++ and vice versa.  Before C99, the characters //  did not introduce a comment in Standard C, and so the sequence of character //* in C could be interpreted differently in C++.

 

3. Operators

    There are three new compound operators in C++:

           .*    ->*    ::

    Since these combinations of tokens would be invalid in Standard C programs, there is no impact on portability from C to C++.

 

4. Identifiers and Keywords

    The identiofiers listed in latter are keywords in C++, but not in C. However, the keyword wchar_t is reserved in Standard C, and the keywords bool, true and false are reserved in C99 as part of the standard libraries.

          asm                   export            private                       throw

          bool                   false               protected                  true

          catch                 friends            public                         try

          class                  mutable          reinterpret_case        typeid

          const_cast         namespace    static_cast                 typename

          delete                new                template                    using

          dynamic_cast    operator          this                            virtual

          explicit                                                                        wchar_t

 

5. Character Constants

    Single-character constants have type int in C, but have type in C++. Multicharacter constants-which are implementation-defined--have type int in both languages. In practice, this makes little difference since in C++ character constants used in integral contexts are promoted to int under the usual conversions. However, sizeof('C') is sizeof(char) in C++, whereas it is sizeof(int) in C.