NAME¶

std::underflow_error - std::underflow_error

Synopsis¶

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).

std-underflow error-inheritance.svg

Inheritance diagram

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)

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.

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 ); (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¶

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

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 added
char* was missing
the explanatory strings of they are the same as that of
LWG 471 C++98 std::underflow_error's the
copies were implementation-defined original std::underflow_error
object