# GDB

**GDB** (the GNU Debugger) lets you inspect and control a running program: pause execution at any line, examine variables, walk the call stack, and step through code. It works on C, C++, Fortran, and other compiled languages by reading debug symbols embedded during compilation.

Instead of scattering `printf` statements and recompiling after every guess, GDB lets you attach to a running process or post-mortem core dump and ask questions directly: what's in this variable, how did we get here, what did the caller pass in?

GDB requires debug information to be useful. Compile with `-O0 -g` for reliable debugging (no optimization, keep debug symbols). Binaries compiled with `-O3` and no `-g` are nearly impossible to debug—the optimizer eliminates the structure GDB needs.

```bash
$ gcc -O0 -g -o app app.c         # compile with debug symbols
$ gdb ./app                         # start debugger
(gdb) break main                    # set breakpoint
(gdb) run                           # run until breakpoint
(gdb) next                          # step over next line
(gdb) print variable                # print variable value
(gdb) quit                          # exit GDB
```

GDB is command-line based. Commands can be abbreviated (e.g., `b` for `break`, `c` for `continue`, `p` for `print`). Press Enter to repeat the last command.

## Concepts

 1. [[gdb-basics|Basics]]
 2. [[gdb-breakpoints|Breakpoints]]
 3. [[gdb-running-and-stepping|Running and stepping]]
 4. [[gdb-examining-state|Examining state]]
 5. [[gdb-inspecting-memory|Inspecting memory]]
 6. [[gdb-call-stack|Call stack]]
 7. [[gdb-watching-expressions|Watching expressions]]
 8. [[gdb-debugging-crashes|Debugging crashes]]
 9. [[gdb-commands|Commands]]
 10. [[gdb-configuration|Configuration]]
 11. [[gdb-tui|TUI (Text User Interface)]]
 12. [[gdb-advanced-features|Advanced features]]