Lab 1: Introduction to NFA->DFA, Subversion, Flex, STL and gdb

How to use Subversion

weesan@eon:~> svn co https://svn.cs.ucr.edu/svn/cs152/weesan
Error validating server certificate for 'https://svn.cs.ucr.edu:443':
 - The certificate is not issued by a trusted authority. Use the
   fingerprint to validate the certificate manually!
Certificate information:
 - Hostname: svn.cs.ucr.edu
 - Valid: from Nov 26 23:58:06 2005 GMT until Nov 26 23:58:06 2006 GMT
 - Issuer: Department of Computer Science and Engineering, UCR, Riverside, California, US
 - Fingerprint: c0:aa:07:ad:16:60:c1:3c:7a:25:2f:0e:47:b3:bb:5e:8b:ec:08:de
(R)eject, accept (t)emporarily or accept (p)ermanently? p
Checked out revision 0.
weesan@eon:~>
weesan@eon:~> cd weesan
weesan@eon:~/weesan>
weesan@eon:~/weesan> svn mkdir lab1
A         lab1
weesan@eon:~/weesan> cd lab1
weesan@eon:~/weesan/lab1>
weesan@eon:~/weesan/lab1> vi README
weesan@eon:~/weesan/lab1> cat README 
WeeSan Lee 
weesan@eon:~/weesan/lab1> 
weesan@eon:~/weesan/lab1> svn ci
Adding         lab1
Adding         lab1/README
Transmitting file data .
Committed revision 1.
weesan@eon:~/weesan/lab1> 
weesan@eon:~/weesan/lab1> cd
weesan@eon:~> 
weesan@eon:~> rm -rf weesan
weesan@eon:~> 
weesan@eon:~> svn co https://svn.cs.ucr.edu/svn/cs152/weesan/lab1
A  lab1/README
Checked out revision 1.
weesan@eon:~> 
weesan@eon:~> cd lab1
weesan@eon:~/lab1> 
weesan@eon:~/lab1> ls -l
total 0
-rw-------  1 weesan csgrads 31 Jan  9 17:41 README
weesan@eon:~/lab1> 
weesan@eon:~/lab1> cat README 
WeeSan Lee 
weesan@eon:~/lab1> 
weesan@eon:~/lab1> cd
weesan@eon:~> rm -rf lab1
weesan@eon:~>

A very simple Flex example

Flex program: lab1.l
%{

/*
 * lab1.l
 *
 * To compile, do the following:
 *   $ flex lab1.l
 *   $ gcc lex.yy.c -o lab1 -lfl
 *
 * To run, do the following:
 *   $ lab1 < Factorial.java
 */

#include <stdio.h>

%}

ws  [ \n\t]+

%%

[A-Za-z0-9_]+ {
    printf("[%s]\n", yytext);
}

{ws} {
}

.

%%

int main(void) {
    yylex();
    return (0);
}

Input file: Factorial.java

class Factorial{
    public static void main(String[] a){
        System.out.println(new Fac().ComputeFac(10));
    }
}

class Fac {
    public int ComputeFac(int num){
        int num_aux ;
        if (num < 1)
            num_aux = 1 ;
        else
            num_aux = num * (this.ComputeFac(num-1)) ;
        return num_aux ;
    }
}

STL examples

List

%{

/*
 * stl_list.l
 *
 * To compile, do the following:
 *   $ flex -t stl_list.l > stl_list.cc
 *   $ g++ stl_list.cc -o stl_list -lfl
 *
 * To run, do the following:
 *   $ stl_list < Factorial.java
 */

#include <stdio.h>
#include <list>
#include <string>

using namespace std;

typedef list<string> ids_t;

static ids_t ids;

%}

ws  [ \n\t]+

%%

[A-Za-z0-9_]+ {
    ids.push_back(yytext);
}

{ws} {
}

.

%%

int main(void) {
    yylex();
    for (ids_t::iterator itr = ids.begin(); itr != ids.end(); itr++) {
	printf("[%s]\n", itr->c_str());
    }
    return (0);
}

Vector

%{

/*
 * stl_vector.l
 *
 * To compile, do the following:
 *   $ flex -t stl_vector.l > stl_vector.cc
 *   $ g++ stl_vector.cc -o stl_vector -lfl
 *
 * To run, do the following:
 *   $ stl_vector < Factorial.java
 */

#include <stdio.h>
#include <vector>
#include <string>

using namespace std;

typedef vector<string> ids_t;

static ids_t ids;

%}

ws  [ \n\t]+

%%

[A-Za-z0-9_]+ {
    ids.push_back(yytext);
}

{ws} {
}

.

%%

int main(void) {
    yylex();
    for (int i = 0; i < ids.size(); i++) {
	printf("[%s]\n", ids[i].c_str());
    }
    return (0);
}

How to use gdb

To debug a program, the program must be compiled with -g flag.
```
    $ gcc -g gdb_ex.c -o gdb_ex
    
```
To debug a program called gdb_ex, run gdb as follow:
```
    $ gdb gdb_ex
    
```

To setup a break point, use 'b' command.

    (gdb) b main
    Breakpoint 1 at 0x8048389: file gdb_ex.c, line 13.
    (gdb)

To run the debugging command in gdb, use 'run' command:

    (gdb) run
    Starting program: /home/weesan/public_html/cs152/lab1/gdb_ex 

    Breakpoint 1, main () at gdb_ex.c:13
    13     func1();
    (gdb)

To list the source code in gdb, use 'list' command:

    (gdb) list
    8 void func1(void) {
    9     func2();
    10 }
    11 
    12 int main(void) {
    13     func1();
    14     return (0);
    15 }
    (gdb)

To single step a statement, use 'n' command:

    (gdb) n
    14     func1();
    (gdb)

To step into a function, use 's' command:

    (gdb) s
    func1 () at gdb_ex.c:9
    9     func2();
    (gdb) 
    (gdb) s
    func2 () at gdb_ex.c:4
    4     int *p = NULL;
    (gdb)

To examine the content of a variable, use 'p' command:

    (gdb) p pt
    $1 = (int *) 0xbfc8f63c
    (gdb) n
    5     *pt = 1234;
    (gdb) p pt
    $2 = (int *) 0x0
    (gdb)

To list all breakpoints, use 'info b' command:

   (gdb) info b
   Num Type           Disp Enb Address    What
   1   breakpoint     keep y   0x08048389 in main at gdb_ex.c:13
    breakpoint already hit 1 time
    (gdb)

To delete a breakpoints, use 'd' command:
```
    (gdb) d 1
    (gdb) 
    
```
To continue the program after stopping at the breakpoint, use 'cont' command:
```
    (gdb) cont
    Continuing.
    
```

To quit gdb, use 'q' command:

    (gdb) q
    The program is running.  Exit anyway? (y or n) y
    $

To examine a core file, do the following from command line:

    $ gdb_ex
    Segmentation fault (core dumped)
    $ gdb gdb_ex core
    GNU gdb 6.3
    ...
    Core was generated by `gdb_ex'.
    Program terminated with signal 11, Segmentation fault.

    warning: current_sos: Can't read pathname for load map: Input/output error

    Reading symbols from /lib/tls/libc.so.6...done.
    Loaded symbols for /lib/tls/libc.so.6
    Reading symbols from /lib/ld-linux.so.2...done.
    Loaded symbols for /lib/ld-linux.so.2
    #0  0x08048364 in func2 () at gdb_ex.c:5
    5     *pt = 1234;
    (gdb)

To examine the stack frames, use 'bt' command:

    (gdb) bt
    #0  0x08048364 in func2 () at gdb_ex.c:5
    #1  0x08048377 in func1 () at gdb_ex.c:9
    #2  0x08048395 in main () at gdb_ex.c:14
    (gdb)

Go to the offended frame, use 'f' command:

    (gdb) f 0
    #0  0x08048364 in func2 () at gdb_ex.c:5
    5     *pt = 1234;
    (gdb)

Go to the upper frame, use 'up' command:

    (gdb) up
    #1  0x08048377 in func1 () at gdb_ex.c:9
    9     func2();
    (gdb)

Go to the lower frame, use 'down' command:

    (gdb) down
    #0  0x08048364 in func2 () at gdb_ex.c:5
    5     *pt = 1234;
    (gdb)

To quit gdb, use 'q' command:
```
    (gdb) q  
    $
    
```