GCC Explorer is awesome, but I would not call it a "C/C++ Fiddle".
It's really slow (unusable) at the moment due to, I reckon, being on HN. Do revisit it later!
I have had some issues with it in the past when importing just iostream and trying to see the output for a small example. The combined source is too large, and GCC Explorer refuses to compile and show the assembly sometimes for even small examples.
Do play with the settings. Colourise is especially nice.
The code is on GitHub [0], so I suppose you can self host it, although I have not tried to do so yet.