Debugging with GDB

The GNU Debugger (gdb) lets you step through code, inspect variables, and set breakpoints.

Typical workflow:

1. Compile with -g flag to embed debug symbols.
2. Start debugging: gdb ./a.out.
3. Set breakpoints: break main or break file.c:line.
4. Run program: run arg1 arg2.
5. Step: next (line‑wise) or step (into functions).
6. Inspect: print var, info locals.
7. Continue: continue.
8. Quit: quit.

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📚 Example Session (pseudo‑output)

$ gcc -g -o sum sum.c
$ gdb ./sum
(gdb) break main
Breakpoint 1 at 0x4005b6: file sum.c, line 5.
(gdb) run 5 7
Starting program: ./sum 5 7
[New Thread 0x7ffff7fd4700 (LWP 1234)]
Breakpoint 1, main (argc=3, argv=0x7fffffffdfd8) at sum.c:5
5       int a = atoi(argv[1]);
(gdb) next
6       int b = atoi(argv[2]);
(gdb) next
7       printf("%d\n", a + b);
(gdb) print a
$1 = 5
(gdb) print b
$2 = 7
(gdb) continue
12
[Inferior 1 (process 1234) exited normally]
(gdb) quit

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📚 Tips

• Use layout src for a source window.
• watch var stops when var changes.
• backtrace (bt) shows the call stack after a crash.