NAME¶

std::runtime_error - std::runtime_error

Synopsis¶

Defined in header <stdexcept>
class runtime_error;

Defines a type of object to be thrown as exception. It reports errors that are due
to events beyond the scope of the program and can not be easily predicted.

Exceptions of type std::runtime_error are thrown by the following standard library
components: std::locale::locale and std::locale::combine.

In addition, the following standard exception types are derived from
std::runtime_error:

* std::range_error
* std::overflow_error
* std::underflow_error

* std::regex_error (since C++11)
* std::system_error

* std::chrono::ambiguous_local_time
* std::chrono::nonexistent_local_time (since C++20)
* std::format_error

std-runtime error-inheritance.svg

Inheritance diagram

Member functions¶

constructor constructs a new runtime_error object with the given message
(public member function)
operator= replaces the runtime_error object
(public member function)

std::runtime_error::runtime_error

runtime_error( const std::string& what_arg ); (1)
runtime_error( const char* what_arg ); (2)
runtime_error( const runtime_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::runtime_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::runtime_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::runtime_error::operator=

runtime_error& operator=( const runtime_error& other ); (noexcept since C++11)

Assigns the contents with those of other. If *this and other both have dynamic type
std::runtime_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::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::runtime_error's the
copies were implementation-defined original std::runtime_error
object