Pointer Qualification Conversions, Casts, and Run-Time Type Identification

Run-Time Type Identification Requirements

Beginning with Release 6.50, the SAS/C C++ Development System supports Run-Time Type Identification, or RTTI. RTTI enables the compiler to automatically generate type information for objects checked at run time. The RTTI option must be specified for each compilation unit to assure that class objects constructed with functions defined in the unit have the information required for dynamic type identification by the dynamic_cast and typeid() operators. See Option Descriptions for more information on the RTTI option. The generated code will abort if the dynamic_cast or typeid() operators are applied to C++ class objects with virtual functions which do not have RTTI information. This means it is generally unsafe to have a program that uses dynamic_cast or typeid() but does not generate RTTI information in all of its compilation units.

Compilation units that do not use dynamic_cast or typeid() can be compiled with the RTTI information. The resulting object files can be safely linked into progams that do not use RTTI. The C++ library is compiled this way. Note that dynamic type identification applies only to C++ classes with virtual functions, so there is no compatibility issue with non-C++ code.

ISO C++ specifies that certain erroneous uses of dynamic_cast and typeid() cause a C++ exception to be thrown. If no exception handler is available, the terminate() operator is called, which aborts the program by default. However, a handler can be specified by set_terminate() to perform cleanup before terminating program execution. See typeinfo.h Header File for more information on these operators.

As an extension to ISO C++, the run-time code for RTTI will detect when dynamic type information is requested for an object that was not compiled with the RTTI option. In such cases, an exception type of std::_ _non_ _rtti is thrown.

The typeid() operator returns a reference to a statically allocated object. The destructor should never be called for this object. Calling typeid() for the same type in different compilation units may produce references to different objects. Always use operator == or operator != to test for type equality.

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