13.48 typeinfo

13.48 <typeinfo>

The <typeinfo> header declares the type_info class (for the typeid operator) and two exception classes related to type information and casting.

bad_cast class

Exception for dynamic_cast<>

---

 class  bad_cast  : public exception { public:  bad_cast  (  ) throw(  );  bad_cast  (const bad_cast&) throw(  );   bad_cast&  operator=  (const bad_cast&) throw(  );   virtual  ~bad_cast  (  ) throw(  );   virtual const char*  what  (  ) const throw(  ); }; 

The dynamic_cast<> operator throws bad_cast when the cast of a reference fails. See dynamic_cast in Chapter 3 for more information.

See Also

dynamic_cast operator

bad_typeid class

Exception for null pointer in typeid expressions

---

 class  bad_typeid  : public exception { public:  bad_typeid  (  ) throw(  );  bad_typeid  (const bad_typeid&) throw(  );   bad_typeid&  operator=  (const bad_typeid&) throw(  );   virtual  ~bad_typeid  (  ) throw(  );   virtual const char*  what  (  ) const throw(  ); }; 

The typeid operator throws bad_typeid when it is applied to an expression of the form *p , in which p is a null pointer. See typeid in Chapter 3 for more information.

See Also

typeid operator

type_info class

Type information

---

 class  type_info  { public:   virtual  ~type_info  (  );   bool  operator==  (const type_info& rhs) const;   bool  operator!=  (const type_info& rhs) const;   bool  before  (const type_info& rhs) const;   const char*  name  (  ) const; private:  type_info  (const type_info& rhs);   type_info&  operator=  (const type_info& rhs); }; 

The typeid operator (described in Chapter 3) returns a static type_info object. The type information includes the type's name and a collation order, both of which are implementation-defined. An implementation might derive classes from type_info to provide additional information.

Note that the copy constructor and assignment operators are inaccessible, so you must store pointers if you want to use a standard container. Example 13-38 shows how to store type_info pointers in a set , where the order is determined by the before member function.

Example

Example 13-38. Storing type information

 #include <algorithm> #include <functional> #include <iostream> #include <ostream> #include <set> #include <typeinfo>     typedef bool (*type_info_compare) (const std::type_info*, const std::type_info*);     typedef std::set<const std::type_info*, type_info_compare>   typeset;     // Return true if *a comes before *b (comparison function to store type_info // pointers in an associative container). bool type_info_less(const std::type_info* a, const std::type_info* b) {   return a->before(*b); }     // Print a type_info name on a line. void print(const std::type_info* x) {   std::cout << x->name(  ) << '\n'; }     void demo(  ) {   // Construct and initialize the set.   typeset types(&type_info_less);       types.insert(&typeid(int));   types.insert(&typeid(char));   types.insert(&typeid(std::type_info));   types.insert(&typeid(std::bad_alloc));   types.insert(&typeid(std::exception));    . . .    // Print the types in the set.   std::for_each(types.begin(  ), types.end(  ), print); } 

The members of type_info are:

bool before (const type_info& rhs) const

Returns true if this type_info object comes before rhs in the implementation-defined order. The relative order of types can vary between programs, even for the same types.

const char* name ( ) const

Returns the type's name as a null- terminated string, which might be a multibyte string. The contents of the name string are implementation-defined.

bool operator== (const type_info& rhs) const

bool operator!= (const type_info& rhs) const

Compares type_info objects, which are equal when the types they describe are the same.

See Also

typeid operator