17 Language support library [support]

17.7 Type identification [support.rtti]

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The header <typeinfo> defines a type associated with type information generated by the implementation.
It also defines two types for reporting dynamic type identification errors.

17.7.1 Header <typeinfo> synopsis [typeinfo.syn]

namespace std {
  class type_info;
  class bad_cast;
  class bad_typeid;
}

17.7.2 Class type_­info [type.info]

namespace std {
  class type_info {
  public:
    virtual ~type_info();
    bool operator==(const type_info& rhs) const noexcept;
    bool before(const type_info& rhs) const noexcept;
    size_t hash_code() const noexcept;
    const char* name() const noexcept;

    type_info(const type_info&) = delete;                   // cannot be copied
    type_info& operator=(const type_info&) = delete;        // cannot be copied
  };
}
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The class type_­info describes type information generated by the implementation ([expr.typeid]).
Objects of this class effectively store a pointer to a name for the type, and an encoded value suitable for comparing two types for equality or collating order.
The names, encoding rule, and collating sequence for types are all unspecified and may differ between programs.
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bool operator==(const type_info& rhs) const noexcept;
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Effects: Compares the current object with rhs.
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Returns: true if the two values describe the same type.
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bool before(const type_info& rhs) const noexcept;
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Effects: Compares the current object with rhs.
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Returns: true if *this precedes rhs in the implementation's collation order.
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size_t hash_code() const noexcept;
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Returns: An unspecified value, except that within a single execution of the program, it shall return the same value for any two type_­info objects which compare equal.
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Remarks: An implementation should return different values for two type_­info objects which do not compare equal.
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const char* name() const noexcept;
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Returns: An implementation-defined ntbs.
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Remarks: The message may be a null-terminated multibyte string, suitable for conversion and display as a wstring ([string.classes], [locale.codecvt]).

17.7.3 Class bad_­cast [bad.cast]

namespace std {
  class bad_cast : public exception {
  public:
    // see [exception] for the specification of the special member functions
    const char* what() const noexcept override;
  };
}
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The class bad_­cast defines the type of objects thrown as exceptions by the implementation to report the execution of an invalid dynamic_­cast expression ([expr.dynamic.cast]).
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const char* what() const noexcept override;
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Returns: An implementation-defined ntbs.

17.7.4 Class bad_­typeid [bad.typeid]

namespace std {
  class bad_typeid : public exception {
  public:
    // see [exception] for the specification of the special member functions
    const char* what() const noexcept override;
  };
}
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The class bad_­typeid defines the type of objects thrown as exceptions by the implementation to report a null pointer in a typeid expression ([expr.typeid]).
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const char* what() const noexcept override;
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Returns: An implementation-defined ntbs.