Visual Studio Code on Linux works really well and is increasingly popular, also a shout out for C-Lion. Eclipse is, umm, eclipsed by them both IMO.

My subjective opinion is that C-Lion is just a little bit more solid/complete, but Microsoft are investing heavily in VScode. It's great to see some serious competition by two well-resourced players working on this stuff.

Personally I'm always happiest with GDB tui. It's all the standard arguments of command-line vs GUI. When you know what you're doing CLI (with tab-complete) is just a faster way to accomplish the task, but when you're a noobie or an infrequent user the GUI wins because it's so much more discoverable.

A nice UI on top of GDB might be all you need. I've used this with some success in the past: https://www.gdbgui.com/

If you're on Windows you can use RemedyBG: https://remedybg.itch.io/remedybg

Try GDB Dashboard, it makes gdb much easier to use:

https://github.com/cyrus-and/gdb-dashboard

There's also Voltron which works with both gdb and lldb (amongst others):

https://github.com/snare/voltron

QtCreator has a very capable debug view. No need to have a Qt project, simply start a binary and step-in into it, or attach to a running process.

Most of IDEs have a similar capability to be able to use debug view without setting up a project.

You can use jetbrain clion an attach it to a binary. Or use even vscode.

Visual Studio, C++ Builder and XCode.

But if you really only need to watch variables any GUI frontend to gdb like QtCreator or DDD will do.

Eclipse-cdt is a reasonable option for this.