NAME¶

std::overflow_error - std::overflow_error

Synopsis¶

Defined in header <stdexcept>
class overflow_error;

Defines a type of object to be thrown as exception. It can be used to report
arithmetic overflow errors (that is, situations where a result of a computation is
too large for the destination type).

The only standard library component that throws this exception is (until C++11)
std::bitset::to_ulong.
The only standard library components that throw this exception are (since C++11)
std::bitset::to_ulong and std::bitset::to_ullong.

The mathematical functions of the standard library components do not throw this
exception (mathematical functions report overflow errors as specified in
math_errhandling). Third-party libraries, however, use this. For example, boost.math
throws std::overflow_error if boost::math::policies::throw_on_error is enabled (the
default setting).

std-overflow error-inheritance.svg

Inheritance diagram

Member functions¶

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

std::overflow_error::overflow_error

overflow_error( const std::string& what_arg ); (1)
overflow_error( const char* what_arg ); (2)
overflow_error( const overflow_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::overflow_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::overflow_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::overflow_error::operator=

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

Assigns the contents with those of other. If *this and other both have dynamic type
std::overflow_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)

Example¶

// Run this code

#include <iostream>
#include <limits>
#include <stdexcept>
#include <utility>

template<typename T, int N>
requires (N > 0) /*...*/
class Stack
{
int top_{-1};
T data_[N];

public:
[[nodiscard]] bool empty() const { return top_ == -1; }

void push(T x)
{
if (top_ == N - 1)
throw std::overflow_error("Stack overflow!");
data_[++top_] = std::move(x);
}

void pop()
{
if (empty())
throw std::underflow_error("Stack underflow!");
--top_;
}

T const& top() const
{
if (empty())
throw std::overflow_error("Stack is empty!");
return data_[top_];
}
};

int main()
{
Stack<int, 4> st;

try
{
[[maybe_unused]] auto x = st.top();
}
catch (std::overflow_error const& ex)
{
std::cout << "1) Exception: " << ex.what() << '\n';
}

st.push(1337);
while (!st.empty())
st.pop();

try
{
st.pop();
}
catch (std::underflow_error const& ex)
{
std::cout << "2) Exception: " << ex.what() << '\n';
}

try
{
for (int i{}; i != 13; ++i)
st.push(i);
}
catch (std::overflow_error const& ex)
{
std::cout << "3) Exception: " << ex.what() << '\n';
}
}

Output:¶

1) Exception: Stack is empty!
2) Exception: Stack underflow!
3) Exception: Stack overflow!

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::overflow_error's the
copies were implementation-defined original std::overflow_error
object