std::underflow_error

 

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Exception categories logic_error invalid_argument domain_error length_error out_of_range runtime_error range_error overflow_error underflow_error tx_exception (TM TS) System error error_category (C++11) generic_category (C++11) system_category (C++11) error_condition (C++11) errc (C++11) error_code (C++11) system_error (C++11) Stacktrace stacktrace_entry (C++23) basic_stacktrace (C++23) Debugging support is_debugger_present (C++26) breakpoint_if_debugging (C++26) breakpoint (C++26)

 

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).

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