How to catch SysError?

[meyerma]

Hello,

I have been seeing SysError in <SomeClass::Method()> error message from time to time. How can we catch it ? I cannot find any SysError class anywhere.

Is it actually cacheable ?

[jonas]

Hi @meyerma,

SysError is not a class, but a function defined in TError.h.

The ROOT errors don’t use any exceptions, so there is nothing to catch. But if you want, you can change the error handler with TError::SetErrorHandler() to something that throws exceptions.

Here is a little example:

void MyErrorHandler(int level, Bool_t abort, const char *location, const char *msg)
{
   if (level == kSysError) {
      std::cout << "it's a SysError!" << std::endl;
      throw std::runtime_error("ROOT had a SysError.");
   }
   DefaultErrorHandler(level, abort, location, msg);
}

void demo()
{

   auto oldHandler = SetErrorHandler(MyErrorHandler);

   SysError("demo", "I am error");

   // Don't forget to reset the error handler
   SetErrorHandler(oldHandler);

   std::cout << "Ending the demo." << std::endl;
}

I would probably only change the error handler only during the part of the code where you want to catch the SysError. Just to control the side effects of that surgery

Cheers,
Jonas

[meyerma]

@jonas

auto oldHandler = SetErrorHandler(MyErrorHandler);

   SysError("demo", "I am error");

   // Don't forget to reset the error handler
   SetErrorHandler(oldHandler);

   std::cout << "Ending the demo." << std::endl;

@jonas This is exactly what I need