Difference between revisions of "cpp/error/underflow error"
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| − | {{cpp/title | underflow_error}} | + | {{cpp/title|underflow_error}} |
| − | {{cpp/error | + | {{cpp/error/navbar}} |
| − | {{ddcl | header=stdexcept | | + | {{ddcl|header=stdexcept| |
class underflow_error; | class underflow_error; | ||
}} | }} | ||
| − | Defines a type of object to be thrown as exception. It | + | Defines a type of object to be thrown as exception. It may be used to report arithmetic underflow errors (that is, situations where the result of a computation is a subnormal floating-point value). |
| + | |||
| + | The standard library components do not throw this exception (mathematical functions report underflow errors as specified in {{lc|math_errhandling}}). Third-party libraries, however, use this. For example, [https://www.boost.org/doc/libs/1_66_0/libs/math/doc/html/math_toolkit/error_handling.html boost.math] throws {{tt|std::underflow_error}} if {{tt|boost::math::policies::throw_on_error}} is enabled (the default setting). | ||
{{inheritance diagram/std-underflow_error}} | {{inheritance diagram/std-underflow_error}} | ||
===Member functions=== | ===Member functions=== | ||
| − | {{ | + | {{cpp/error/exception/member of derived with message|underflow_error}} |
| − | + | ||
| − | {{ | + | {{cpp/error/runtime_error/inherit}} |
{{cpp/error/exception/inherit}} | {{cpp/error/exception/inherit}} | ||
| + | |||
| + | ===Defect reports=== | ||
| + | {{dr list begin}} | ||
| + | {{dr list item|wg=lwg|dr=254|std=C++98|before=the constructor accepting {{c|const char*}} was missing|after=added}} | ||
| + | {{dr list item|wg=lwg|dr=471|std=C++98|before=the explanatory strings of {{tt|std::underflow_error}}'s<br>copies were implementation-defined|after=they are the same as that of the<br>original {{tt|std::underflow_error}} object}} | ||
| + | {{dr list end}} | ||
| + | |||
| + | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | ||
Latest revision as of 10:17, 11 September 2023
| Defined in header <stdexcept>
|
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| class underflow_error; |
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Defines a type of object to be thrown as exception. It may be used to report arithmetic underflow errors (that is, situations where the result of a computation is a subnormal floating-point value).
The standard library components do not throw this exception (mathematical functions report underflow errors as specified in math_errhandling). Third-party libraries, however, use this. For example, boost.math throws std::underflow_error if boost::math::policies::throw_on_error is enabled (the default setting).
Inheritance diagram
Contents |
[edit] Member functions
| (constructor) |
constructs a new underflow_error object with the given message (public member function) |
| operator= |
replaces the underflow_error object (public member function) |
std::underflow_error::underflow_error
| underflow_error( const std::string& what_arg ); |
(1) | |
| underflow_error( const char* what_arg ); |
(2) | |
| underflow_error( const underflow_error& other ); |
(3) | (noexcept since C++11) |
std::underflow_error then std::strcmp(what(), other.what()) == 0. No exception can be thrown from the copy constructor.Parameters
| what_arg | - | explanatory string |
| other | - | another exception object to copy |
Exceptions
Notes
Because copying std::underflow_error 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.
Before the resolution of LWG issue 254, the non-copy constructor can only accept std::string. It makes dynamic allocation mandatory in order to construct a std::string object.
After the resolution of LWG issue 471, a derived standard exception class must have a publicly accessible copy constructor. It can be implicitly defined as long as the explanatory strings obtained by what() are the same for the original object and the copied object.
std::underflow_error::operator=
| underflow_error& operator=( const underflow_error& other ); |
(noexcept since C++11) | |
Assigns the contents with those of other. If *this and other both have dynamic type std::underflow_error then std::strcmp(what(), other.what()) == 0 after assignment. No exception can be thrown from the copy assignment operator.
Parameters
| other | - | another exception object to assign with |
Return value
*this
Notes
After the resolution of LWG issue 471, a derived standard exception class must have a publicly accessible copy assignment operator. It can be implicitly defined as long as the explanatory strings obtained by what() are the same for the original object and the copied object.
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)
|
[edit] 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 254 | C++98 | the constructor accepting const char* was missing | added |
| LWG 471 | C++98 | the explanatory strings of std::underflow_error'scopies were implementation-defined |
they are the same as that of the original std::underflow_error object
|
