GDB Tutorial

Launching

To use GDB you must compile with the -g compiler flag. This is so the compiler and linker keep all the useful debugging information (symbol and code information).
Launch GDB by telling it what program to debug: gdb myProgram or cgdb myProgram.
NOTE: You could run your program at this point, but it won't be useful for debugging. You'd want to set a breakpoint first.
If you want to run your program use the run command (shorthand: r).
To quit GDB use the quit command (shorthand: q).

Breakpoints

Breakpoints can be set using the break command (shorthand: b).

There are multiple ways to set breakpoints, by:

line number: b 6
function name: b foo
file name and line number: b foo.c:6

Make things easier by setting a breakpoint before running your program.

Set it on the first line using b 1
Run your program using r.

By doing this you can step through your program one line at a time.

NOTE: A breakpoint stops execution before the line of code is executed.

Stepping

Step into the current line with the step command (shorthand: s) when execution is paused.For example, if execution is paused on the line x = foo();, the command s will enter foo() and break at the first line of foo().

Step over the current line with the next command (shorthand: n). It will execute all the code until it reaches the next line in the current scope.In the case of x = foo();, all of foo() will be executed and its returned value will be assigned to x. Execution will then pause on the line that comes after x = foo();.

Step out of a function with the finish command (shorthand: fin). It will finish the current function and pauses execution once the function is completed.

Complete execution of a loop from the last line of the loop using the until command and execution will resume on the line below it.

Resume normal execution with the continue command (shorthand: c); it'll stop at the next breakpoint.

Program State

View the value of a variable (when execution is paused) with the print foo command (shorthand: p foo). You can even view the result of an expression, such as p listContainsFoo().

Change the value of a variable with the set foo = 10 command.

Show the stack with the info stack command (shorthand: i s). View stack frame #3 with the frame 3 command.

Advanced Breakpoints

Conditional breakpoints are used to pause execution only if some condition is met.

You can create them with expressions.For example, b 6 if x == 0 or b 6 if listContainsFoo().

See the list of current breakpoints with the info breakpoints command (shorthand: i b).NOTE: Each breakpoint is given a number.

Delete a breakpoint in two ways:

Delete a breakpoint given its breakpoint number: delete 1 (shorthand: d 1)
Follow the same rules you used to create the breakpoint: clear foo.c:6 (shorthand: cl foo.c:6)

Temporarily disable a breakpoint with the disable 1 command (shorthand: dis 1).

Re-enable breakpoints with the enable 1 command (shorthand: en 1).

CAUTION: The clear command shorthand is cl. The continue command shorthand is c. You do not want to mix up these two.