temporary object deconstructor throwing an exception

Question

Suppose I have the following code. The first try-catch behaves as expected. I get a "caught hello". The second try catch, instead, reports caught 0x501da8 (a pointer). In the second case, a temporary stringstream subclass is created. In its destructor (thus before the base aka stringstream is deconstructed) I call str of the underlying stringstream, and use it to create the runtime_error. Why does the code does not work in the second case? (compiling with -fno-elide-constructors makes no difference)

#include <sstream>
#include <iostream>
#include <stdexcept>

class S:public std::stringstream{
public:   
  ~S(){      
    throw std::runtime_error(str());
  }
};


void f(){
  S a;  
  a<<"hello";
}

void g(){
  S()<<"hello";
}

int main(){
  try{
    f();
  }catch(std::runtime_error& b){
    std::cout<<"caught "<<b.what()<<std::endl;
  }

  try{
    g();
  }catch(std::runtime_error& b){
    std::cout<<"caught "<<b.what()<<std::endl;
  }
}

The ideas was the following. Create an "exception stream" where I << all the error details, and let the destructor throw (so I am sure I cannot forget to throw once I created the stream). Something like if (failcondition){ S()<<"some error "<<someinfo; } Is there a way to properly achieve such behavior?

thank you, Indeed I was reading https://stackoverflow.com/questions/130117/throwing-exceptions-out-of-a-destructor — Fabio Dalla Libera, Mar 12 '18 at 06:24
You must be building as C++03, I suppose. Because your code is not valid C++11 or later. — StoryTeller - Unslander Monica, Mar 12 '18 at 06:25
it compiles ( g++ --std=c++11) but yeah, constructurs should default to noexcept,isn't it? — Fabio Dalla Libera, Mar 12 '18 at 06:26
They do default to noexcept. And you can't change that specification when overriding (the ios_base d'tor is noexcept by default). So your code should not do anything other than call `std::terminate`. — StoryTeller - Unslander Monica, Mar 12 '18 at 06:27
the ideas was the following. Create an "exception stream" where I << all the error details, and let the destructor throw (so I am cannot forget to throw once I created the stream). Something like if (failcondition){ S()<<"some error "< — Fabio Dalla Libera, Mar 12 '18 at 07:32
Maybe something like Andrescu's `Expected` (essentially the Maybe monad) would be a good fit? — Jens, Mar 12 '18 at 07:57

temporary object deconstructor throwing an exception

0 Answers0