std::rethrow_exception

 

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Defined in header <exception>
[[noreturn]] void rethrow_exception( std::exception_ptr p );		(since C++11) (constexpr since C++26)

See More

Throws the previously captured exception object referred-to by the exception pointer p, or a copy of that object.

It is unspecified whether a copy is made. If a copy is made, the storage for it is allocated in an unspecified way.

The behavior is undefined if p is null.

Parameters

p

-

non-null std::exception_ptr

Exceptions

The exception object referred-to by p if no copy is made.

Otherwise, a copy of such exception object if the implementation successfully copied the exception object.

Otherwise, std::bad_alloc or the exception thrown when copying the exception object, if allocation or copying fails, respectively.

Notes

Before P1675R2, rethrow_exception was not allowed to copy the exception object, which is unimplementable on some platforms where exception objects are allocated on the stack.

Feature-test macro	Value	Std	Feature
__cpp_lib_constexpr_exceptions	202411L	(C++26)	constexpr for exception types

Example

Run this code

#include <exception>
#include <iostream>
#include <stdexcept>
#include <string>

void handle_eptr(std::exception_ptr eptr) // passing by value is OK
{
    try
    {
        if (eptr)
            std::rethrow_exception(eptr);
    }
    catch(const std::exception& e)
    {
        std::cout << "Caught exception: '" << e.what() << "'\n";
    }
}

int main()
{
    std::exception_ptr eptr;

    try
    {
        [[maybe_unused]]
        char ch = std::string().at(1); // this generates a std::out_of_range
    }
    catch(...)
    {
        eptr = std::current_exception(); // capture
    }

    handle_eptr(eptr);

} // destructor for std::out_of_range called here, when the eptr is destructed

Possible output:

Caught exception: 'basic_string::at: __n (which is 1) >= this->size() (which is 0)'

See also

exception_ptr (C++11)	shared pointer type for handling exception objects (typedef)
current_exception (C++11)	captures the current exception in a std::exception_ptr (function)