std::ios_base:: failure
|
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.
|
|
(since C++17) |
Inheritance diagram |
(until C++11) |
Inheritance diagram |
(since C++11) |
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) | |
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.
|
The returned string is encoded with the ordinary literal encoding during constant evaluation. |
(since C++26) |
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
)
|
|
|
[virtual]
|
returns an explanatory string
(virtual public member function of
std::system_error
)
|
Inherited from std:: runtime_error
Inherited from std:: exception
Member functions
|
[virtual]
|
destroys the exception object
(virtual public member function of
std::exception
)
|
|
[virtual]
|
returns an explanatory string
(virtual public member function of
std::exception
)
|
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.
- ↑ 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 .
Example
#include <fstream> #include <iostream> 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
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 48 | C++98 |
the constructor overload (1) initialized the base class
std::exception
with msg , but the base class does not have a matching constructor |
corresponding
description removed |
| LWG 331 | C++98 |
std::ios_base::failure
declared a destructor without
throw
(
)
|
removed the destructor declaration |
See also
|
(C++11)
|
the IO stream error codes
(enum) |