std::ios_base::failure - cppreference.com (original) (raw)

| Defined in header | | | | ----------------------------------------------------------------- | | | | class failure; | | |

The class std::ios_base::failure defines an exception object that is thrown on failure by the functions in the Input/Output library.

Inheritance diagram	(until C++11)
Inheritance diagram	(since C++11)

Contents

• 1 Member functions
• 2 std::ios_base::failure::failure
  • 2.1 Parameters
  • 2.2 Notes
• 3 std::ios_base::failure::operator=
  • 3.1 Parameters
  • 3.2 Return value
• 4 std::ios_base::failure::what
  • 4.1 Return value
  • 4.2 Notes
• 5 Inherited from std::system_error
  • 5.1 Member functions
• 6 Inherited from std::runtime_error
• 7 Inherited from std::exception
  • 7.1 Member functions
  • 7.2 Notes
  • 7.3 Example
  • 7.4 Defect reports
  • 7.5 See also

[edit] Member functions

| | constructs a new failure object with the given message (public member function) | | ---------------------------------------------------------------------------------- | | | replaces the failure object (public member function) | | | returns the explanatory string (public member function) |

std::ios_base::failure::failure

1,2) Constructs the exception object using message as explanation string which can later be retrieved using

what()

. ec is used to identify the specific reason for the failure.(since C++11)

1. Copy constructor. Initialize the contents with those of other. If *this and other both have dynamic type std::ios_base::failure then std::strcmp(what(), other.what()) == 0.(since C++11)

Parameters

Notes

Because copying std::ios_base::failure is not permitted to throw exceptions, this message is typically stored internally as a separately-allocated reference-counted string. This is also why there is no constructor taking std::string&&: it would have to copy the content anyway.

std::ios_base::failure::operator=

| failure& operator=( const failure& other ); | | (until C++11) | | ----------------------------------------------------- | | ------------- | | failure& operator=( const failure& other ) noexcept; | | (since C++11) |

Assigns the contents with those of other. If *this and other both have dynamic type std::ios_base::failure then std::strcmp(what(), other.what()) == 0 after assignment.(since C++11)

Parameters

Return value

*this

std::ios_base::failure::what

| virtual const char* what() const throw(); | | (until C++11) | | ------------------------------------------- | | ------------- | | virtual const char* what() const noexcept; | | (since C++11) |

Returns the explanatory string.

Return value

Pointer to an implementation-defined null-terminated string with explanatory information. The string is suitable for conversion and display as a std::wstring. The pointer is guaranteed to be valid at least until the exception object from which it is obtained is destroyed, or until a non-const member function (e.g. copy assignment operator) on the exception object is called.

Notes

Implementations are allowed but not required to override what().

Inherited from std::system_error

Member functions

| | returns error code (public member function of std::system_error) [edit] | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | returns an explanatory string (virtual public member function of std::system_error) [edit] |

Inherited from std::exception

Member functions

| | destroys the exception object (virtual public member function of std::exception) [edit] | | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | returns an explanatory string (virtual public member function of std::exception) [edit] |

[edit] Notes

Before the resolution of LWG issue 331, std::ios_base::failure declared a destructor without throw(), where std::exception::~exception() was declared with throw()[1]. This means the std::ios_base::failure::~failure() had a weaker exception specification. The resolution is to remove that declaration so that the non-throwing exception specification is kept.

LWG issue 363 targets the same defect and its resolution is to add throw() to the declaration of std::ios_base::failure::~failure(). That resolution was not applied due to the conflict between the two resolutions.

1. ↑ The non-throwing exception specification is now applied globally across the standard library, so the destructors of standard library classes are not declared with throw() or noexcept.

[edit] Example

#include #include   int main() { std::ifstream f("doesn't exist");   try { f.exceptions(f.failbit); } catch (const std::ios_base::failure& e) { std::cout << "Caught an ios_base::failure.\n" << "Explanatory string: " << e.what() << '\n' << "Error code: " << e.code() << '\n'; } }

Possible output:

Caught an ios_base::failure. Explanatory string: ios_base::clear: unspecified iostream_category error Error code: iostream:1

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also