c++exceptiontry-catchc++buildercatch-block

How to get the current exception object in C++ Builder (replacement for ExceptObject)?


I am looking for a function/code that returns the current exception object. In other words, the exception object that represents the exception currently being handled (by the catch block).

For example:

  try
  {
    // throws an exception
  }
  catch (const std::exception& Exc)
  {
    DoSomething();
  }

void DoSomething() {
  // How to get the "Exc" here?
}

In other words, I need a C++ equivalent of Delphi's ExceptObject function.

The code above is just an example. The real code looks more like this:

  catch (...)
  {
    A3rdPartyCode();
  }

void A3rdPartyCode() {
  MyCode();
}

void MyCode() {
  // Does not work, returns NULL:
  TObject* = ExceptObject(); 

  // ???
  // Need to know the current exception, if present
}

Solution

  • Most likely you are looking for a solution in the wrong way, trying to match Delphi and C++ line for line. Anyway, here's an example of how std::current_exception can be used:

    #include <iostream>
    #include <exception>
    
    void f()
    {
      throw "exception from f()";
    }
    
    std::exception_ptr pce;
    
    void g() noexcept
    {
      try
      {
        f();
      }
      catch (...)
      {
        pce = std::current_exception();
      }
    }
    
    void h() noexcept
    {
      try
      {
        if ( pce )
          std::rethrow_exception(pce);
      }
      catch (const char* e)
      {
        std::cout << e;
      }
    }
    
    int main()
    {
      g();
      h();
    }
    

    std::current_exception is useful, for example, if you are processing a collection in a secondary thread using a function that can throw for each item in the collection. Instead of interrupting the processing, you can store the exception and forward it to the main thread later.