C stuff

How to add non-printable characters to a string

 strcat(test2,"\x01");  01 -- is non-printable ascii character.

 

 

I will be updating the new stuff which come across in C language here, Hope it will be useful. 1. is the header file contains bool datatypes. 2. To read strings from the keyboard we can use two functions: fgets() -- reads a line from fd specified, it will also '\n' which u pass after giving the string so u need to over write it with '\0' . getchar() -- reads character by character. scanf() -- can be used but "white space" is the delimiter in the scanf, if the string has a "white space" in it the string will be treated as two strings. 3. strchr(, ) will retun the address of the character in the string if it is, or else it will return null. 4. every running program will associated with three standard files -- stdout, stderr,stdin. fflush() - Input/Output is nearly 1000 times slower than your processor. Thus it makes no sense for your code to stop executing while the system is writing data somewhere. (you have no choice but to wait if it is reading data - after all you need to do something with it) So what systems do is, store that data into a buffer to output it (to disk or screen) later, and continue executing your program... But what if you do not want this lazy thing to happen. Say you want to tell the user - "everything is written to pen drive. safe to remove pen drive" and there is your lazy system which will do this later!! This is the place to say fflush - (short for flush file) that forces all input/output to complete. It is a common, though incorrect practice to use fflush on the input stream, in order to clear any extraneous input left behind by a scanf function. This may not work in all compilers, and should generally be avoided. File operations: fopen(), fclose(), rewind(), fseek(), fgets(), fputs() void perror(const char *s); --The perror() function shall map the error number accessed through the symbol errno to a language-dependent error message, which shall be written to the standard error stream malloc(),calloc() and realloc(): void *malloc(size_t size): Returns unintialized memory of size "size", retuns "null" if memory is not available. void *calloc(size_t nelem, size_t elsize): Returns intialized memory with 0 of nelem variables of size "elsize". void *realloc(void *ptr, size_t size): changes the size of the object pointed to by ptr to the size specified by size, and returns a pointer to the possibly moved block. The contents are unchanged up to the lesser of the new and old sizes. If ptr is null, realloc() behaves like malloc() for the specified size. If size is zero (0) and ptr is not a null pointer, the object pointed to is freed.

BSNL Broadband

Over come ""error 676: the phone line busy"
GOTO DSL ROUTER SITE (http://192.168.1.1).. PASSWORD N LOGIN ID IS
"ADMIN"
AND CLICK ON ADVANCE SETUP THEN CLICK ON WAN ...

HERE U WILL SEE SOME VALUES (((VPI/VCI 0/35 Con. ID Category Service
Interface Protocol Igmp QoS State ))) AND ON 1ST OPTION {VPI/VCI 0/35}
TICK THE REMOVE OPTION AND REMOVE IT......THEN CLICK ON ADD OPTION AND CLICK NEXT NEXT AND LAST SAVE IT

....U HAVE TO DO NOTHING;;; DONT CHANGE ANYTHING VALUES THAT WILL COME ..ALL ARE PRE SET AND SO AFTER SAVE
CLICK ON SAVE/REBOOT.......
UR DONE .......... .....
THIS IS SOLUTION FOR PHONE

Not able to connect to the router 192.168.1.1 says page cannot be displayed
go to your local area connection's properties
in tcp/ip connections keep it to :use the following ip address" then in
ip address = 192.168.1.2
subnet mask = 255.255.255.0 (automatically it will take or else you type it)
default gateway = 192.168.1.1

PPPoE & Bridge mode:
PPPoE
(1) PPPoE modem is an always connected mode.(userid and password stored in modem)
(2) For getting good speed with torrents ports are required to be forwarded.
(3) For connecting multiple PCs modem must be in PPPoE mode.
(4) Telenet scripts are required for scheduled automatic booting and re booting.
(5) More secured.

Bridge mode
(1) Connects to net through dialer by entering userid and password
(2) No need of port forwarding for torrents as all ports are open
(3) Telenet scripts are not required for scheduled downloads.
(4) Strong firewalls required as as all ports r open.


Reference:
change from bridge mode to pppoe mode: http://www.chennai.bsnl.co.in/BBS/Wireless/WirelessSecurity.htm#WA3002_Modem_configuration:
http://www.indiabroadband.net/bsnl-broadband/10489-phone-line-busy-error-ut300r2u-modem-here-100-solution.html
http://www.indiabroadband.net/bsnl-broadband/15507-not-able-connect-router-192-168-1-1-says-page-cannot-displayed.html
http://www.indiabroadband.net/bsnl-broadband/8088-pppoe-bridge-mode.html
http://en.kioskea.net/forum/affich-91194-bsnl-wifi-iti-dna-a211-1

About GDB

GDB is a wonderful tool if you are using linux as your platform for software development.
I will list done some of the frequently used approaches here.

watch point:

awatch *0x8092581000

rwatch *0x8092581000

it will start breaking whenever there is read/write at: 0xa87c0e255f7f0080

find /g 0x8080000000,0x8092581000, 0x8080459578
-- this is to search for value: 0x8080459578 between address 0x8080000000 && 0x8092581000
find  0x8080000000,0x8092581000, "tbl_sm_main"
-- this is to search a string. 

 

Printf usage

printf "Delete object: %d\n", i

Commands:
1. info frame
 -- will list down the registry level info about the particular frame, it will be useful when you are debugging cores.
2. info args
  -- will list the arguments passed to the function in particular frame.
3. disassemble
  -- will give the assembly code for the function.
4. disassemble 0xf1704f0 0xf17050f
  -- will give the assembly code between two addresses
5.  info registers
  -- will give the details of registers and stored values
6. info reg OR x $
  -- will output the contents for regiser, ex1: info reg r32 ex2: x $r32
7. info source
8. info sources
9. set pagination on/off
10. x/32w 0x100f3000
  -- To print 32 words from address 0x100f3000
11. x/s

  -- To print contents of the address as string
12. x/nc

  -- To print content of the address as character, it will print "n" characters starting from the address.
13. x/t

  -- To print in binary
14. x/nx

  -- To print in hexa
15. core
  -- To attached to the core file
16. generate-core-file
  -- To generate a core at the particular instance on a running process.
17. set follow-fork-mode parent/child/ask
  -- To set whether to follow parent or child or ask whom to follow.
18.  show follow-fork-mode
  -- To display the status of fork mode
19. set history expansion on

  -- To enable capturing history, you can "!" to rerun the olde commands as similar to Bash command.

20. set height

21. set width 

   -- To set width of the screen. if the lines in gdb are not wrapping after giving above command then run "shell reset" to make it work properly

22. set confirm off/on

  -- Disables/Enables confirmation requests

23. show confirm

   -- Displays the status of confirmation requests

24. show convenience

   -- Print a list of convenience variables used so far, and their values. Abbreviated show conv.

      Convenience variables are prefixed with `$'. Any name preceded by `$' can be used  for a 

      convenience variable, unless it is one of the predefined machine-specific register names.

25. output/fmt expression

   -- Print the value of expression and nothing but that value: no newlines, no `$nn = '. 

      The value is not entered in the value history either. You can use the same formats as for print.

26. set print pretty on/off

   -- Cause GDB to print structures in an indented format with one member per line.

27. show print pretty

   -- Show which format GDB is using to print structures.  

28. info proc map

   -- to list process memory mapping

29.  maintenance info sections

   -- to list core memory mapping

30. info files

   -- list the memory mapping of all the files 

31. info line <function name>

   -- display 

32. add-symbol-file <library.so> .txt 

  -- we can get.txt address of library from info files.

  -- this will help adding loading symbol files manually

To allow the system to dump the core:

ulimit -c unlimited

History related commands:

These commands display the state of the GDB history parameters.


show history

show history filename

show history save

show history size

show history expansion

show commands

Display the last ten commands in the command history.

show commands n

Print ten commands centered on command number n.

show commands +

Print ten commands just after the commands last printed.

 

Logging related commands:

show logging                    # displays weather logging is on / off
set logging on                  # enable logging
set logging off                 # disable logging
set logging file log-file.txt   # set name for log file, default is gdb.txt

set logging overwrite   # To append logs of debug sessions or

                                 create new on every debug session using 

 

 

 Good post on checkpoints:

http://sourceware.org/gdb/onlinedocs/gdb/Checkpoint_002fRestart.html#Checkpoint_002fRestart

 

Tracing function calls of process through gdb:

http://stackoverflow.com/questions/311840/tool-to-trace-local-function-calls-in-linux#312058

Breaking the process whenever a function from a specific file is getting executed:

http://stackoverflow.com/questions/475283/using-gdb-stop-the-program-when-it-is-using-any-function-from-file-x

default configuration file for gdb is: .gdbinit

To print the size of the structure in GDB:
p sizeof(struct ) ---- make sure symbol for the structure is present.

Breakpoints:

break FUNCTION

Set a breakpoint at entry to function FUNCTION.

break LINENUM

Set a breakpoint at line LINENUM in the current source file.

break FILENAME:LINENUM

Set a breakpoint at line LINENUM in source file FILENAME.

break FILENAME:FUNCTION

Set a breakpoint at entry to function FUNCTION found in file FILENAME.

break ... if COND

Set a breakpoint with condition COND; evaluate the expression COND each time the breakpoint is reached, and stop only if the value is nonzero--that is, if COND evaluates as true. ... stands for one of the possible arguments described above (or no argument) specifying where to break.

To generate core dumps during program running:
#include
void assert(int expression);
If expression evaluates to 0 (false), then the expression, sourcecode filename, and line number are sent to the standard error, and then calls the abort function.
To enable core dumps for your current shell, use ulimit to set a maximal core dump size in megabytes.
For this example, we'll "limit" core dumps to 1 gigabyte:
$ulimit -c 1024

To use macros in the gdb use following option during compiling:

gcc -gdwarf-2 -g3 sample.c -o sample

#define NDEBUG === > then the macro assert does nothing.

References:
http://sourceware.org/gdb/onlinedocs/gdb/Forks.html
http://arioch.unomaha.edu/~jclark/gdb_plus.html
http://discussknowhow.blogspot.com/2008/07/analyzing-core-dumps-and-assert.html
http://developer.apple.com/mac/library/documentation/DeveloperTools/gdb/gdb/gdb_10.html
http://www.haifux.org/lectures/222/GDB_haifux_David_Khosid.pdf -- Advanced debbuging with gdb
GNU Debugger - Advanced GDB Actions - GoldhiveWiki

http://sunsite.ualberta.ca/Documentation/Gnu/gdb-4.18/html_chapter/gdb_15.html

http://web.mit.edu/gnu/doc/html/gdb_10.html 

https://eli.thegreenplace.net/2011/09/06/stack-frame-layout-on-x86-64

Compilers

I like to put some words on compilers sooner or later. So starting this article. In the meanwhile I will be adding articles I came across.

References:
1. http://www.linuxjournal.com/content/examining-compilation-process-part-1
2. http://gcc.gnu.org/onlinedocs/cpp/Preprocessor-Output.html#Preprocessor-Output

File recovery

References:
1. http://www.makeuseof.com/tag/3-remarkable-file-recovery-tools/
2. http://www.makeuseof.com/tag/restore-your-deleted-files-easily-with-recuva/
3. http://www.makeuseof.com/tag/recover-lost-computer-files-with-undelete-plus/
4. http://www.makeuseof.com/tag/recover-deleted-files-from-your-linux-system/
5. http://www.geekgirls.com/windows_recycle_bin.htm

IP Fragmentation

Encapsulation:
When a host or router handles a datagram, the IP software determines the next hop to which the datagram should be sent. Thus a datagram could traverse many physical networks, each with their own frame formats. An IP datagram is encapsulated in the data area of the frame.

MTU:
The basic fact in networking is that not all networking technologies were created equal. One of the differences between various layer-2 technologies is the maximum payload (commonly called Maximum Transmission Unit – MTU) a layer-2 frame can transport.

Fragmentation:
IP uses a technique called fragmentation to solve the problem of heterogeneous MTUs. When a datagram is larger than the MTU of the network over which it must be sent, it is divided into smaller fragments which are each sent separately.

Path MTU Discovery: The generic solution to the IP fragmentation issues should be the Path MTU Discovery that was issued as an RFC.
It works by setting the DF (Don't Fragment) option in the IP headers of outgoing packets. Any device along the path whose MTU is smaller than the packet will drop such packets and send back an ICMP "Destination Unreachable (Datagram Too Big)" message containing its MTU, allowing the source host to reduce its assumed path MTU appropriately. The process repeats until the MTU is small enough to traverse the entire path without fragmentation.

References:
http://penguin.dcs.bbk.ac.uk/academic/networks/network-layer/fragmentation/index.php
http://www-inteng.fnal.gov/Integrated_Eng/software/locsys/syscode/ipsoftware/IPFragmentation.html
http://www.nil.si/ipcorner/IP_Fragmentation/

Format USB drive

Long long ago I used to format external memory devices. But recently when I needed an USB to be formatted because of virus, interestingly I forgot the method to do it. So I thought of adding this info here for future reference.

steps:
1. First, connect your USB device to your computer. Then right-click on My Computer from the desktop and choose Manage.
2. Next click on Device Manager and then expand out Disk Drives. You should see your USB drive listed there as “Generic USB 2.0 USB Drive” or something similar.
3. Now right-click on the USB drive under Disk Drives and choose Properties. Then go to the Policies tab.
4. Now you will see two options, the “Optimize for quick removal” selected by default. Go ahead and change that by selecting the “Optimize for performance” option. This enables writing caching on the drive and therefore allows you to format it as NTFS! Sweet.
5. That’s it. Now click OK and then go to My Computer. Right click on the drive in My Computer and choose Format. In the File System drop down you will now see the option for NTFS!

References:
http://www.online-tech-tips.com/computer-tips/format-usb-ntfs/

Cscope with vim

today I came to know the best way of using cscope with vim(I mean through ex editor commands).

SHORTCUT:
Ctrl-b will browse through history of cscope searches that u performed earlier at the cscope prompt.

first set the default editor to vim
export EDITOR=vim

• Find this definition - :cs f g
• Find functions called by this function - :cs f d
• Find functions calling this function - :cs f c
• Find this text string - :cs f t
• Find this file - :cs f f
• Find files #including this file - :cs f i
• Find this C symbol - :cs f s
• Find this egrep pattern - :cs f e

if you see problem in building the cscope database or facing problem like "E567: no cscope connections" then use:

:cs add cscope.out
as described under ":help cscope-howtouse"

Is the screen getting unresponsive/blocked/can't reattach, then try setting following command next time:
:nonblock on (or) -- default is 1 second.
:nonblock 5 

To browse the code through commands instead of typing ":cs f x",
download the following file:
http://cscope.sourceforge.net/cscope_maps.vim
copy it to:
~/.vim/plugin directory (assuming u are using >=vim6) and follow the following command options and I can tell you it's worth trying and with this options cscope became best browsing tool for me:

• To jump to a result type the results number (+ enter)
• Use tags commands to return after a jump to a result: ctrl-t
  To return to same spot as departure, use ctrl-o
• To use "tags" navigation to search for words under the cursor (ctrl-\ or ctrl-])
• CTRL-\ s/g/c/f..etc for key board shortcuts
• "CTRL-spacebar s". This time, your Vim window will split in two horizontally , and the Cscope search result will be put in the new window. [if you've never used multiple Vim windows before: move between windows via 'CTRL-W w' (or CTRL-W arrow key, or CTRL-W h/j/k/l for left/up/down/right), close a window via 'CTRL-W c' (or good old ':q'), make the current window the only one via 'CTRL-W o', split a window into two via 'CTRL-W s' (or 'CTRL-W v' for a vertical split), open a file in a new window via ':spl[it] filename']
• "CTRL-spacebar CTRL-spacebar s" (just hold down the CTRL key and tap the spacebar twice). If you have trouble hitting the keys fast enough for this to work, go into the cscope_maps.vim script and change Vim's timeout settings as described in the comments This time your Vim window will be split vertically

To get the help from vim :help cscope or :cs help
Command to see the runtimepath of vim :set runtimepath

Building cscope database on readonly workspace

Create cross reference file with readonly directories or files by giving complete path:
1. cscope -R -s dir,dir,dir -f cross-reference.file --- if this doesn't work, try the following:
     Go to one of the directories for which you need to build database, because -s option seems to take including the current directory to build database. Here lets think you are in dirpath1
    cscope -R -s  dirpath2/* dirpath3/*  -f cross-reference.file
2. cscope -R /complete-path/file1.c /complete-path/file.h -f cross-reference.file
3. find `pwd` -name [*.ch] | sort > file
cscope -R -i file -f cross-reference.file

To just start with cross-reference file
cscope -d -f cross-reference.file

To display last n elements of the path name:
cscope -pn 


To set the cscope tags:
set cst


>>>>>>
set csprg=/router/bin/cscope



References:
http://vimdoc.sourceforge.net/htmldoc/if_cscop.html
http://www.swaroopch.com/notes/Vim_en:Programmers_Editor
http://vim.dindinx.net/orig/html/if_cscop.txt.php
http://www.uic.edu/depts/accc/software/unixgeneral/vi101.html
http://vim.sourceforge.net/scripts/script.php?script_id=213
http://www.vim.org/scripts/script.php?script_id=1638
http://www.vim.org/scripts/script.php?script_id=2502
http://www.yolinux.com/TUTORIALS/LinuxTutorialAdvanced_vi.html
http://cscope.sourceforge.net/cscope_vim_tutorial.html
http://uw714doc.sco.com/en/SDK_cdebug/B_CmdLnOpts.html
http://unix.stackexchange.com/questions/46568/gnu-screen-freezes-trying-to-reattach

c errors

incompatible types in assignment
example:
int a[10];
a = malloc(10);

About VNC

vncserver -- Starting vnc server.
vncserver : 1 -- Starting vnc server with specific session.
vncserver -kill :1 -- Killing the vncsession.
vncconfig & -- to make copy paste work b/w remote to local vice versa.

On linux to have VNC connection to current session:
For this you need to install x11vnc:

x11vnc -display :0 -auth ~/.Xauthority

We can start the vnc during bootup aswell. Please google it for this.


Following is the config file which I use in ~user/.vnc/xstartup file:
**************************
#!/bin/sh
if [ `/bin/uname` = "SunOS" ] ; then
xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic -nowin&
xterm -geometry 80x24+10+10 -sb -ls -sl 8000 -title "$VNCDESKTOP Desktop" &
blackbox &
else # Linux
vncconfig -nowin -set AlwaysShared=on &
PATH=$PATH:/usr/X11R6/bin:/usr/bin:/usr/cisco/bin:/usr/X11R6/bin
export PATH
WM=/usr/bin/startxfce4
#WM=/usr/X11R6/bin/twm
#WM=/usr/bin/gnome-session
#WM=/usr/bin/startkde
fi
if [ ! -x $WM ] ; then
# failsafe window manager choice
WM=twm
fi
if [ -r $HOME/.Xdefaults ] ; then
xrdb -merge $HOME/.Xdefaults
fi
## following config is for copy/paste from vnc viewer.
if [ -x /usr/bin/vncconfig ]; then
/usr/bin/vncconfig -nowin &
elif [ -x /usr/cisco/bin/autocutsel ] ; then
/usr/cisco/bin/autocutsel &
fi
exec $WM
*******************************

References:
http://www.karlrunge.com/x11vnc/
http://ubuntuforums.org/showthread.php?t=944187

Linux Bash Commands

1. echo $SHELL -- to know the current shell

2. chsh -s /bin/bash - to change the current shell.
3. echo $SHELLOPTS - Which shell mode is being used (vi or emacs)
4. set -o emacs - to set shell mode to emacs
5. By default bash doesn't check it's window size after every command. The good thing is that you can make it. Add "shopt -s checkwinsize" to your ~/.bashrc or /etc/profile.

echo "shopt -s checkwinsize" >> ~/.bashrc (or /etc/profile)
source ~/.bashrc
try again

6. Problem: rm: cannot chdir from `festival/' to `config': Permission denied
Solution: chmod -R u+rwx * in the directory
7. Yet to come.

Bash Shell Keyboard Shortcuts:
Moving around:
Ctrl-b - Move a character backwards.
Ctrl-f - Move a character forward.
Alt-b - Move cursor backward one word on the current line.
Alt-f - Move cursor forward one word on the current line.
Ctrl-a - Move to the beginning of the current line.
Ctrl-e - Move to the end of the current line.
Ctrl-x-x - to the start, and to the end again

Cut, copy and paste:
Ctrl-d - Delete the character the cursor is on.
Ctrl-h - Delete a character before the cursor.
Ctrl-u - Delete from the cursor back to the line start.
Ctrl-k - Delete from the cursor to the end of the line.
Ctrl-x Backspace - Delete all characters in the line up till the current cursor position.
Alt-d - Delete the word, starting at the current cursor position.
Alt-Backspace - Delete every character from the current cursor position to the first character of a word that is encountered.
Ctrl-w - Delete the word, untill after the previous word boundary.
Ctrl-y - Yank/Paste previous killed text at the cursor position.
Alt-y - Yank/Paste previous previous killed text at the cursor position.

History
Ctrl-p - Move in history to the previous line.
Ctrl-n - Move in history to the next line.
Ctrl-r - Incrementally search the line history, Backwardly.
Ctrl-s - Incrementally search the line history, Forwardly.
Ctrl-J - End an incremental search.
Ctrl-G - Abort an incremental search and restore the original line.
Alt-Ctrl-y - Yank/Paste arg. 1 of prev. cmnd at the cursor position.
Alt-. OR Alt-_ - Yank/Paste last arg of prev. cmnd at the cursor position.

Undo
Ctrl-_ OR Ctrl-x OR Ctrl-u - Undo the last editing command; you can undo all the way back to an empty line.
Alt-r - Undo all changes made to this line.
Ctrl-l - Clear the screen, reprinting the current line at the top

Completion
TAB - Auto-complete a name.
Alt-/ - Auto-complete a name (without smart completion).
Alt-? - List the possible completions of the preceeding text.
Alt-* - Insert all possible completions of the preceeding text.

Transpose
Ctrl-t - Swap (transpose) the characters the cursor is on, and the character before the cursor.
Alt-t - Swap (transpose) the current word with the previous word.

CASE
Alt-u - Make the word uppercase, starting at the current cursor position.
Alt-l - Make the word lowercase, starting at the current cursor position.
Alt-c - Capitalize the current word character or the next word character that is encountered.

Use "set t_ti= t_te=" in .vimrc
if you don't want clear vim output after exit vim. 

References:
http://www.slackbasics.org/html/chap-shell.html
http://faq.programmerworld.net/misc/linux-keyboard-shortcuts.html
http://article.gmane.org/gmane.linux.gentoo.user/57011
http://www.linuxquestions.org/questions/linux-general-1/disable-the-clear-after-you-close-vi-657233/#post3221832
http://www.bigsmoke.us/readline/shortcuts

oldest eatery in Bangalore

1. Udupi Krishna Bhavan, Chickpet
2. Malabar, Chickpet
3. New Modern Café, Near Minerva cisrcle
4. Vidyarthi Bhavan, Basavanagudi -- special for dosas
5. MTR, Lalbagh Gate
6. Veena Stores, Malleshwaram
7. Sri Sagar, Malleshwaram
8. Surya Stores, Malleshwaram
9. Hotel Janata, Maleeshwaram
10. Brahmins Coffee Bar in Shankarpuram -- special for idlis
11. New modern hotel (NMH) near minerva circle
12. Dwarka Bhavan in NR Colony
13. SLV hotel near ramakrishna ashrama -- special for kharabath
14. Iyer Mess in malleswaram -- for south indian meals
15. Janatha Hotel (Masala Dose) in Malleswaram
16. Ragiguda SLV in Jayanagar-- for ravva idli
17. Siddappa Hotel (Butter dosa)-- (you need to take left on the Corporation signal after Pallavi Theater. Move around close to 100ft and take another left. Pass a Govt.. school which kinda semi-circle and you’ll be in front of the hotel.)
18. Muddanna (Idlys & Pulav) in Cubbon pet - Near Town Hall
19. Chikkana (Dosas with Ghee) - in Cubbon Pet
20. Food Street (south indian & north indian) - VV Puram
21. Indian Coffe house - (Snacks) - Vidhan Soudha
22. Gundappa Hotel -- (Badam halwa and mouth watering mysore pak)
23. Hotel Gopika (also called as New Krishna Bhavan) opp to Mantri Greens(Known for authentic and unique karavali food (Neer Dose, Green Masala idle, Kotte kadubu, gojju avalakki, paddu))

links:
http://www.triphobo.com/blog/best-dosa-joints-in-bangalore
http://www.triphobo.com/blog/restaurants-in-bangalore-serving-kannada-food

Melodies

Yamuna Thatilo --- Dalapathi
Alanaati --- Murari
Kammani --- Guna
Paruvam vaanala --- Roja