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std::underflow_error

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underflow_error
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Defined in header <stdexcept>
class underflow_error;

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).

cpp/error/exceptioncpp/error/runtime errorstd-underflow error-inheritance.svg

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)
(3)
underflow_error( const underflow_error& other );
(until C++11)
underflow_error( const underflow_error& other ) noexcept;
(since C++11)
1) Constructs the exception object with what_arg as explanatory string. After construction, std::strcmp(what(), what_arg.c_str()) == 0.
2) Constructs the exception object with what_arg as explanatory string. After construction, std::strcmp(what(), what_arg) == 0.
3) Copy constructor. If *this and other both have dynamic type std::underflow_error then std::strcmp(what(), other.what()) == 0. No exception can be thrown from the copy constructor. (until C++11)

Parameters

what_arg - explanatory string
other - another exception object to copy

Exceptions

1-2) May throw std::bad_alloc

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 );
(until C++11)
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. (until C++11)

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

[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's
copies were implementation-defined
they are the same as that of the
original std::underflow_error object