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std::ios_base::failure

From cppreference.com
< cpp‎ | io‎ | ios base
 
 
 
 
Defined in header <ios>
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.

std::ios_base::failure may be defined either as a member class of std::ios_base or as a synonym (typedef) for another class with equivalent functionality.

(since C++17)
cpp/error/exceptionstd-ios base-failure-2003-inheritance.svg

Inheritance diagram

(until C++11)
cpp/error/exceptioncpp/error/runtime errorcpp/error/system errorstd-ios base-failure-inheritance.svg

Inheritance diagram

(since C++11)

Contents

[edit] Member functions

(constructor)
constructs a new failure object with the given message
(public member function)
operator=
replaces the failure object
(public member function)
what
returns the explanatory string
(public member function)

std::ios_base::failure::failure

(1)
explicit failure( const std::string& message );
(until C++11)
explicit failure( const std::string& message,
                  const std::error_code& ec = std::io_errc::stream );
(since C++11)
explicit failure( const char* message,
                  const std::error_code& ec = std::io_errc::stream );
(2) (since C++11)
(3)
failure( const failure& other );
(until C++11)
failure( const failure& other ) noexcept;
(since C++11)
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)
3) 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

message - explanatory string
ec - error code to identify the specific reason for the failure
other - another failure to copy

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

other - another exception object to assign with

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.

Parameters

(none)

Return value

Pointer to a 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]
[virtual]
returns an explanatory string
(virtual public member function of std::system_error) [edit]

Inherited from std::runtime_error


Inherited from std::exception

Member functions

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

[edit] Example

#include <iostream>
#include <fstream>
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';
    }
}

Output:

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

[edit] See also

(C++11)
the IO stream error codes
(enum) [edit]