C++ Library Conventions

The C++ library obeys much the same conventions as the Standard C Library, plus a few more outlined here.

An implementation has certain latitude in how it declares types and functions in the C++ library:

Names of functions in the Standard C library may have either extern "C++" or extern "C" linkage. Include the appropriate Standard C header rather than declare a library entity inline.
A member function name in a library class may have additional function signatures over those listed in this document. You can be sure that a function call described here behaves as expected, but you cannot reliably take the address of a library member function. (The type may not be what you expect.)
A library class may have undocumented (nonvirtual) base classes. A class documented as derived from another class may, in fact, be derived from that class through other undocumented classes.
A type defined as a synonym for some integer type may be the same as one of several different integer types.
A bitmask type can be implemented as either an integer type or an enumeration. In either case, you can perform bitwise operations (such as AND and OR) on values of the same bitmask type. The elements A and B of a bitmask type are nonzero values such that A & B is zero.
A library function that has no exception specification can throw an arbitrary exception, unless its definition clearly restricts such a possibility.

On the other hand, there are some restrictions:

The Standard C Library uses no masking macros. Only specific function signatures are reserved, not the names of the functions themselves.
A library function name outside a class will not have additional, undocumented, function signatures. You can reliably take its address.
Base classes and member functions described as virtual are assuredly virtual, while those described as nonvirtual are assuredly nonvirtual.
Two types defined by the C++ library are always different unless this document explicitly suggests otherwise.
Functions supplied by the library, including the default versions of replaceable functions, can throw at most those exceptions listed in any exception specification. No destructors supplied by the library throw exceptions. Functions in the Standard C Library may propagate an exception, as when qsort calls a comparison function that throws an exception, but they do not otherwise throw exceptions.

See also