Hello I am doing trying to use the debugger in cs50 IDE.

However it will always hang here on "listening to port 15470" after I click the "run" button.

enter image description here

I have no idea what the problem is or how to fix it. I have looked at all the other related questions asked about debugging on here but have still found no answers.

Please help.


I had the same problem. What seems to be working for me is running debug50 ./programname from the terminal.


Google "cs50 gdb youtube" and you will find two helpful videos explaining how to use the debugger from the command line. It's much more reliable, and has the added benefit of being a tool that will always be available to you in the future even if you do not use the Cloud9 IDE for development.

Basically, to debug myprog with a breakpoint at myfunc, passing arguments arg1 and arg2, do the following:

gdb ./myprog
break myfunc
run arg1 arg2

After that, you can step forward with n, or step into a function with s. Use info args to view arguments, info locals to view local variables, and p foo to print the value of variable foo.

To debug functions in multiple files, set your breakpoints and then as you are stepping through statements with n, pay attention and when you get to the line that calls the externally-defined function, step into it with s instead.

EDIT: Downvoted for this advice? Really? I'm surprised.

I'm back at my desk now, and I can see your screenshot more clearly than I could on my phone. Now, I can see that you are trying to debug count.c from Module 1.

I can remember what it was like to start Module 1. I felt over my head at first, and I'm sure you probably do too.

I apologize if I gave you advice that was more appropriate for your future self! In Module 2, you will learn about functions, arguments, and all the other jargon I used above. :)

I decided to take a crack at the graphical debugger myself just to see if I could help you better. I set a breakpoint on line 23: int main(void). Then, I clicked the "Run" button and it looked as though everything was paused, just as you described.

That's because the program was paused. Its execution was suspended at my breakpoint. This is exactly what's supposed to happen!

Then, I clicked on the "Resume" button. It's a blue triangle that looks like a "Play" button on a CD player, and I found it at the top left corner of the right sidebar.

Clicking this caused the triangle to change into two vertical bars, like the "Pause" button on a CD player. It also caused my program's execution to Resume, and then I had to look down at the bottom to see that the program had printed a prompt and was waiting for my input. It said Please enter a number: and GetInt() was waiting for me to enter a number!

Hopefully this helps you to run the graphical debugger. Come back and read my initial advice when you are working on pset3 -- it will make much more sense to you then!

EDIT2: I'm back on mobile and can't test this now, but I believe that the problem the commenter below is having has to do with running the debugger without any breakpoints. You have to set a breakpoint, or the debugger won't let you inspect anything during execution! Also, I stopped using the graphical debugger by Module 3, because I found it unreliable.

My original advice stands: get to know the command-line gdb. You'll thank yourself later. I am certain that I would have been unable to complete some of the later problem sets (especially speller.c and server.c) without it!


If it's any consolation, other people are having this problem too, and the general consensus is that the Terminal debugger is much more reliable than the graphical debugger.

  • 1
    The problem is happening on my IDE as well, and it doesn't seem to stem from setting a breakpoint in the wrong place. Instead, it compiles the code and then hangs at the "listening to port 15470" line when no breakpoints are in the program, without actually running through the code. No play or pause button appears in the debugging menu because the menu doesn't initialize yet.
    – Dash
    Aug 18 '16 at 2:32
  • Thank you for the response. It still hangs at the same point when I place breakpoints in the program (at places in main or outside of main). So the problem seems to occur regardless of breakpoints.
    – Dash
    Aug 18 '16 at 23:35
  • 1
    I think something is wrong with the graphical debugger for me; but I have taken your advice and learnt to use the terminal debugger.
    – Andy Lyell
    Aug 30 '16 at 13:13
  • If you look at the runner for C/C++ GDB it actually spawns an instance of gdbserver (with the --once parameter too!) So, the implication here is that the runner allows the application to be connected to remotely from another machine. You could then open a terminal on your local machine and communicate with gdbserver using port 15470. While this is better than nothing, I admit it would make more sense to debug native code from within the IDE via some loopback mechanism. I already have a terminal in cloud9 so I could run gdb or cgdb as is. So... it's nice but not what I was looking for. Mar 20 '17 at 17:57

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