std::current_exception
(C++17)<exception>
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.
This function can be called in a std::terminate_handler to retrieve the exception which has provoked the invocation of std::terminate .
Contents
[edit] 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 .
[edit] Notes
On the implementations that follow Itanium C++ ABI (GCC, Clang, etc), exceptions are allocated on the heap when thrown (except for std::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.
On Windows in managed CLR environments [1], the implementation will store a std::bad_exception when the current exception is a managed exception ([2]). Note that catch(...) catches also managed exceptions:
#include <exception> int main() { try { throw gcnew System::Exception("Managed exception"); } catch (...) { std::exception_ptr ex = std::current_exception(); try { std::rethrow_exception (ex); } catch (std::bad_exception const &) { // This will be printed. std::cout << "Bad exception" << std::endl ; } } }
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_constexpr_exceptions |
202411L |
(C++26) | constexpr for exception types |
[edit] Example
#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)'