NAME¶

std::current_exception - std::current_exception

Synopsis¶

Defined in header <exception>
std::exception_ptr current_exception() noexcept; (since C++11)

If called during exception handling (typically, in a catch clause), captures the
current exception object and creates an std::exception_ptr that holds either a copy
or a reference to that exception object (depending on the implementation). The
referenced object remains valid at least as long as there is an exception_ptr object
that refers to it.

If the implementation of this function requires a call to new and the call fails,
the returned pointer will hold a reference to an instance of std::bad_alloc.

If the implementation of this function requires copying the captured exception
object and its copy constructor throws an exception, the returned pointer will hold
a reference to the exception thrown. If the copy constructor of the thrown exception
object also throws, the returned pointer may hold a reference to an instance of
std::bad_exception to break the endless loop.

If the function is called when no exception is being handled, an empty
std::exception_ptr is returned.

Parameters¶

(none)

Return value¶

An instance of std::exception_ptr holding a reference to the exception object, or a
copy of the exception object, or to an instance of std::bad_alloc or to an instance
of std::bad_exception.

Notes¶

On the implementations that follow Itanium C++ ABI (GCC, Clang, etc), exceptions are
allocated on the heap when thrown (except for bad_alloc in some cases), and this
function simply creates the smart pointer referencing the previously-allocated
object, On MSVC, exceptions are allocated on stack when thrown, and this function
performs the heap allocation and copies the exception object.

Example¶

// Run this code

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

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 {
std::string().at(1); // this generates an 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"

See also¶

exception_ptr shared pointer type for handling exception objects
(C++11) (typedef)
rethrow_exception throws the exception from an std::exception_ptr
(C++11) (function)
make_exception_ptr creates an std::exception_ptr from an exception object
(C++11) (function template)
uncaught_exception
uncaught_exceptions checks if exception handling is currently in progress
(removed in C++20) (function)
(C++17)