8.4 Using Runtime Functions and Predefined Exceptions

The standard header <exception> provides the classes and exception-related functions specified in the C++ standard. You can access this header only when compiling in standard mode (compiler default mode, or with option -compat=5). The following excerpt shows the <exception> header file declarations.

// standard header <exception>
namespace std {
    class exception {
           exception() throw();
           exception(const exception&) throw();
           exception& operator=(const exception&) throw();
           virtual ~exception() throw();
           virtual const char* what() const throw();
    };
    class bad_exception: public exception {...};
    // Unexpected exception handling
       typedef void (*unexpected_handler)();
       unexpected_handler
         set_unexpected(unexpected_handler) throw();
       void unexpected();
    // Termination handling
       typedef void (*terminate_handler)();
       terminate_handler set_terminate(terminate_handler) throw();
       void terminate();
       bool uncaught_exception() throw();
}

The standard class exception is the base class for all exceptions thrown by selected language constructs or by the C++ standard library. An object of type exception can be constructed, copied, and destroyed without generating an exception. The virtual member function what() returns a character string that describes the exception.

For compatibility with exceptions as used in C++ release 4.2, the header <exception.h> is also provided for use in standard mode. This header allows for a transition to standard C++ code and contains declarations that are not part of standard C++. Update your code to follow the C++ standard (using <exception> instead of <exception.h>) as development schedules permit.

// header <exception.h>, used for transition
#include <exception>
#include <new>
using std::exception;
using std::bad_exception;
using std::set_unexpected;
using std::unexpected;
using std::set_terminate;
using std::terminate;
typedef std::exception xmsg;
typedef std::bad_exception xunexpected;
typedef std::bad_alloc xalloc;