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/C++std::underflow_error
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) | |
| (3) | ||
underflow_error( const underflow_error& other ); | (until C++11) | |
underflow_error( const underflow_error& other ) noexcept; | (since C++11) |
what_arg as explanatory string. After construction, std::strcmp(what(), what_arg.c_str()) == 0.what_arg as explanatory string. After construction, std::strcmp(what(), what_arg) == 0.*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
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) |
|
[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'scopies were implementation-defined | they are the same as that of the original std::underflow_error object |
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