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Basic Guide to Debugging with GDB

Debugging with GDB (GNU Debugger) is an essential tool for finding and fixing errors in your code. Here’s a basic guide to help you get started:

Compiling and Running the Program

1. Compile with debugging information: gcc -g -o program program.c
2. Start gdb with the program: gdb program
3. Set a breakpoint: break [function/line number]
4. Run the program: run [arguments]

Controlling Program Flow

• break [function/line number]: Set a breakpoint at the specified function or line number.
• delete [optional number]: Delete all breakpoints or just the optional number one.
• continue: Continue running the program until the next breakpoint is hit or the program exits.
• next: Execute the current line and move to the next line in the source code, without stepping into function calls.
• step: Execute the current line and step into any function calls on that line.
• until [optional line]: Run the program until it reaches the specified line or until the current function returns.

Information Commands

• info breakpoints: List all breakpoints.
• info functions: List all functions in the program.
• info variables: List all global variables in the program.
• info locals: List all local variables in the current function.
• backtrace: Show the current call stack.
• info [args]: Display various types of information, such as info breakpoints, info functions, info locals, and more.

Print file’s code

• frame: (or f) show current line (with argument, changes the frame)
• list [optional line]: (or l) Show 10 lines of the code starting at the optional line (also works with list 1,10 to list lines 1 through 10).

Data Manipulation

• print [expression]: Evaluate the specified expression and print its value.
• set [variable]=[value]: Change the value of the specified variable.
• display [expression]: Print the value of the specified expression every time gdb stops.

Miscellaneous Commands

• watch [expression]: Set a watchpoint on the specified expression, so that gdb will break whenever that expression is modified.
• finish: Run the program until the current function returns.
• set print pretty on: Enable pretty-printing for complex data structures.
• set print elements [number]: Set the number of elements gdb will print when displaying arrays and structures.
• set follow-fork-mode [parent/child]: Set the follow-fork-mode for debugging forked processes.
• set detach-on-fork [on/off]: Set whether gdb will automatically detach from forked processes.
• set pagination [on/off]: Set whether gdb will pause after displaying a full screen of output.

To quit gdb, simply type quit.