Get help

While in a debug session, any of the following commands could be used as the next action for starting the actual debugging of the project:

n: Step through the program, proceeding through subroutine calls.
l: List the specified function or line.
break: Set a breakpoint on the specified function or line.
help: Get the help main menu.
help data: Get the help data menu.
help inspect: Get help for the inspect command.
inspect y: Inspect the contents of variable y.
set y=3: Assign a value to variable y.
bt: Get a back trace.

For more information about these commands and their arguments, see the Using GDB appendix in this guide, or use the help cmd command in gdb.

Let's see how to use some of these basic commands.

# The list command:
    (gdb) l
    3
    4   main () {
    5
    6       int x,y,z;
    7
    8       setprio (0,9);
    9       printf ("Hi ya!\n");
    10
    11      x=3;
    12      y=2;

# Press <enter> to repeat the last command:
    (gdb) <enter>
    13      z=3*2;
    14
    15      exit (0);
    16
    17  }

# Break on line 11:
   (gdb) break 11
   Breakpoint 2 at 0x80483c7: file hello.c, line 11.

# Continue until the first breakpoint:
    (gdb) c
    Continuing.
    Hi ya!

    Breakpoint 2, main () at hello.c:11
    11      x=3;

# Notice that the above command went past the
# printf statement at line 9. I/O from the
# printf statement is displayed on screen.

# Inspect variable y, using the short form of the
# inspect command:
    (gdb) ins y
    $1 = -1338755812
    
# Get some help on the step and next commands:
    (gdb) help s
    Step program until it reaches a different source line.
    Argument N means do this N times (or till program stops
    for another reason).
    (gdb) help n
    Step program, proceeding through subroutine calls.
    Like the "step" command as long as subroutine calls don't
    happen; when they do, the call is treated as one instruction.
    Argument N means do this N times (or till program stops
    for another reason).

# Go to the next line of execution:
    (gdb) n
    12      y=2;
    (gdb) n
    13      z=3*2;
    (gdb) inspect z
    $2 = 1
    (gdb) n
    15      exit (0);
    (gdb) inspe z
    $3 = 6

# Continue program execution:
    (gdb) continue
    Continuing.

    Program exited normally.

# Quit the debugger session:    
    (gdb) quit
    The program is running. Exit anyway? (y or n) y
    (61) con1 /home/allan/src >