C++ Exceptions Rethrow (propagate) exception


Example

Sometimes you want to do something with the exception you catch (like write to log or print a warning) and let it bubble up to the upper scope to be handled. To do so, you can rethrow any exception you catch:

try {
    ... // some code here
} catch (const SomeException& e) {
    std::cout << "caught an exception";
    throw;
}

Using throw; without arguments will re-throw the currently caught exception.

C++11

To rethrow a managed std::exception_ptr, the C++ Standard Library has the rethrow_exception function that can be used by including the <exception> header in your program.

#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