This demonstrates basic gdb commands. See the other sample for an actual debugging session with comments explaining the actions.
Green text is from gdb or Linux; red text is from swap.cpp; black text is user input
Script started on Mon 07 Sep 2009 01:37:12 PM EDT
[hermes.cs.kent.edu]{1}-> g++ -g -o swap swap.cpp
[hermes.cs.kent.edu]{2}-> gdb swap
GNU gdb Fedora (6.8-27.el5)
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i386-redhat-linux-gnu"...
(gdb) l
2 // allowing for repeats
3 // Example for demo of gdb
4 //JWB
5 #include <iostream>
6 using namespace std;
7 int main () {
8 int i;
9 char a,b, more;
10 do {
11 cout << "Input character values for a and b : ";
(gdb) l
12 cin >> a;
13 cout << "\nOriginally a is " << a << " and b is " << b << endl;
14
15 //do swap
16 a = b;
17 b = a;
18
19 //output results
20 cout << "\nAfter the swap a is now " << a << " and b is now " << b << endl;
21
(gdb) r
Starting program: /users/cs/faculty/jbaker/cs1-alt/swap
Input character values for a and b : AB
Originally a is A and b is ¿
After the swap a is now ¿ and b is now ¿
Input c to continue; s to stop :
Input character values for a and b : AB
Originally a is A and b is ¿
After the swap a is now ¿ and b is now ¿
Input c to continue; s to stop :
Input character values for a and b :
Program received signal SIGINT, Interrupt.
0x003aa410 in __kernel_vsyscall ()
(gdb) b 1 [K [K [Kl 13
8 int i;
9 char a,b, more;
10 do {
11 cout << "Input character values for a and b : ";
12 cin >> a;
13 cout << "\nOriginally a is " << a << " and b is " << b << endl;
14
15 //do swap
16 a = b;
17 b = a;
(gdb) b 13
Breakpoint 1 at 0x80487f0: file swap.cpp, line 13.
(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /users/cs/faculty/jbaker/cs1-alt/swap
Input character values for a and b : AB
Breakpoint 1, main () at swap.cpp:13
13 cout << "\nOriginally a is " << a << " and b is " << b << endl;
(gdb) p a
$1 = 65 'A'
(gdb) pb [K b Note: The [K is a backspace where the user changed the entry
from pb to p b
$2 = -65 '¿'
(gdb) p b='B" [K'
$3 = 66 'B'
(gdb) c
Continuing.
Originally a is A and b is B
After the swap a is now B and b is now B
Input c to continue; s to stop :
Input character values for a and b :
Program received signal SIGINT, Interrupt.
0x001f3410 in __kernel_vsyscall ()
(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /users/cs/faculty/jbaker/cs1-alt/swap
Input character values for a and b : AB
Breakpoint 1, main () at swap.cpp:13
13 cout << "\nOriginally a is " << a << " and b is " << b << endl;
(gdb) n
Originally a is A and b is ¿
16 a = b;
(gdb) n
17 b = a;
(gdb) n
20 cout << "\nAfter the swap a is now " << a << " and b is now " << b << endl;
(gdb) n
After the swap a is now ¿ and b is now ¿
22 cout << "Input c to continue; s to stop : ";
(gdb) n
23 cin >> more;
(gdb) p more
$4 = 18 '\022'
(gdb) quit
The program is running. Exit anyway? (y or n) y
[hermes.cs.kent.edu]{3}-> exit
Script done on Mon 07 Sep 2009 01:41:21 PM EDT