std::current_exception
Defined in header <exception> | ||
std::exception_ptr current_exception()noexcept; | (since C++11) (constexpr since C++26) | |
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_exceptionconst&){// 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(conststd::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)'
[edit]See also
(C++11) | shared pointer type for handling exception objects (typedef) |
(C++11) | throws the exception from an std::exception_ptr (function) |
(C++11) | creates an std::exception_ptr from an exception object (function template) |
(removed in C++20*)(C++17) | checks if exception handling is currently in progress (function) |
