17 Language support library [support]

17.9 Exception handling [support.exception]

17.9.2 Class exception [exception]

namespace std {
  class exception {
  public:
    exception() noexcept;
    exception(const exception&) noexcept;
    exception& operator=(const exception&) noexcept;
    virtual ~exception();
    virtual const char* what() const noexcept;
  };
}

The class exception defines the base class for the types of objects thrown as exceptions by C++ standard library components, and certain expressions, to report errors detected during program execution.

Each standard library class T that derives from class exception has the following publicly accessible member functions, each of them having a non-throwing exception specification ([except.spec]):

(2.1)
default constructor (unless the class synopsis shows other constructors)
(2.2)
copy constructor
(2.3)
copy assignment operator

The copy constructor and the copy assignment operator meet the following postcondition: If two objects lhs and rhs both have dynamic type T and lhs is a copy of rhs, then strcmp(lhs.what(), rhs.what()) is equal to 0.

The what() member function of each such T satisfies the constraints specified for exception::what() (see below).

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exception(const exception& rhs) noexcept;
exception& operator=(const exception& rhs) noexcept;

Postconditions: If *this and rhs both have dynamic type exception then the value of the expression strcmp(what(), rhs.what()) shall equal 0.

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virtual ~exception();

Effects: Destroys an object of class exception.

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virtual const char* what() const noexcept;

Returns: An implementation-defined ntbs.

Remarks: The message may be a null-terminated multibyte string, suitable for conversion and display as a wstring ([string.classes], [locale.codecvt]).

The return value remains valid until the exception object from which it is obtained is destroyed or a non-const member function of the exception object is called.