c++ - std::exception_ptr 复制构造函数可以抛出吗？

Question

在我看来，标准允许 std::exception_ptr 不使用引用计数(即 std::exception_ptr cctor 可以复制异常对象指着)。这意味着 following code可能永远不会调用 handle_eptr() 并且异常可以逃逸 main() 并产生相关后果:

#include <iostream>
#include <string>
#include <exception>
#include <stdexcept>
 
void handle_eptr(std::exception_ptr eptr) // passing by value is ok  <---- ARE YOU SURE?
{
    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

我说的对吗？

Answer 1

Can std::exception_ptr copy constructor throw?

没有。

标准说(最新草案):

[propagation]

exception_­ptr meets the requirements of Cpp17NullablePointer

[nullablepointer.requirements]

No operation which is part of the Cpp17NullablePointer requirements shall exit via an exception.