some ways to recover loss packet

o. FEC (forward error correction)

o. Interleaving

o. Packet Repetition

o. Interpolation

memset 問題

Function: void * memset ( void * ptr, int value, size_t num );

Today, when I use memset function to initialize a buffer to "0" , I found that the number of byte must to the actually byte of the buffer+1..

However, The third variable of memset is Number of bytes to be set to the value.

Still don't know the reason of this

如何在codeblocks設定連結winsock library

exec codeblocks

Settings > Compiler and Debugger > Linker Settings > Add >

Go to CodeBlocks Folder (normally C:\Program Files\CodeBlocks)

then MingW then libs and find libws2_32.a and add it.

what is analysis exactly?

Analysis is the process of breaking a complex topic or substance into smaller parts to gain a better understanding of it.
(from wikipedia)

製作強制關機捷徑 on windows

1. 在桌面按右鍵->新增->捷徑

2. 在輸入項目的位置處 輸入 shutdown -s -t 50 -c "shutdown message"意思是系統會在50秒內強制關機

3. 按下一步完成

4. 點選剛剛新增好的捷徑測試

warning: 請先存檔尚未儲存的檔案

very humorous R example code

fun <- function() {

ANSWER <- readline("Are you a satisfied R user? ")

if (substr(ANSWER, 1, 1) == "n")

cat("This is impossible. YOU LIED!\n")

else

cat("I knew it.\n")

}

fun()

[LOOP] loop problem

問題:

mac address 衝突 產生 loop message - loop(1) xx.xx.xx.xx.xx.xx to ex1 from ex0. (active)

解決過程:

先看到錯誤訊息, 把訊息中ip mac 傳送的source and destination 畫出來.

發現從不同網卡傳送的封包具有相同的mac address. 結果發現ap 與我的電腦的mac address竟然一樣.

就發現當初在設定ap的時候有個功能是複製你的PC的mac address. 這個功能可能是為了方便填寫mac.

然後你自己要在修改mac address. 不知道為什麼ap 沒有自己預設的mac address而要自己設置.

linux and human.

[bug] x200 has 48 hours battery life

如何檢視Linux系統distribution版本

cat /etc/*release
cat /etc/issue

[Ruby] string format

"%.3f" % (1.0/7) # "0.143"
"%5.1f" % 345.6789 # "345.7"

"%05d" % 123 # "00123"
"%-5s" % "ID" # "ID "
"%04x" % 0xfc14 # "fc14"

"%6.2f, %05d" % [345.6789,123] # "345.68, 00123"
"%-5s: %04x" % ["ID", 0xfc14] # "ID : fc14"

vi 復原跟做

in command mode, use u key to undo and Ctr-r key to redo.

[FUN]chrome 可以開幾個tab 呢?

a lot of tabs.

[指令] WC - 印出文件 行數 字數 byte數

指令： wc

參數：

-c, --bytes               印出位元數

-m, --chars              印出字數 印出該文件有幾個字

-l, --lines                 印出該文件有幾行   

-L, --max-line-length 印出該文件最長的那行有幾字

-w, --words              印出單字數目

This is just a note to prevent me forgot it. :P

[問題] switch 裡面放switch 時 default: 的問題

error: ‘default’ label in scope of identifier with variably modified type not containing enclosing switch statement

to be solved...

解決在OS X 使用terminal遠端使用screen無法backspace的情況

In terminal program, choose preferences -> advanced;

select "Delete sends Ctrl+H"

done!

About unistd.h

在unix-like的系統內, unistd.h所定義的介面大多由一些system call的函式所組成, 像是fork, pipe 以及一需 基本IO

(read, write, open, close) 等等

malloc vs new

Difference between uses of new/malloc & delete/free:

(a) Operator new constructs an object (calls constructor of object), malloc does not.
(b) Operator new is an operator, malloc is a function.
© Operator new can be overloaded, malloc cannot be overloaded.
(d) Operator new throws an exception if there is not enough memory, malloc returns a NULL.
(e) Operator new[] requires to specify the number of objects to allocate, malloc requires to specify the total number of bytes to allocate.
(f) malloc() returns void *, which has to be explicitly cast to the desired type but new returns the proper type.
(g) Operator new/new[] must be matched with operator delete/delete[] to deallocate memory, malloc() must be matched with free() to deallocate memory.
(h) The new/delete couple does not have a realloc alternative that is available when malloc/free pair is used. realloc is used to resize the length of an array or a memory block dynamically.

reference:http://c.ittoolbox.com/groups/technical-functional/cpp-l/malloc-vs-new-1255507

codeploy? It's hard to use it

Recently, I tried to use codeploy to upload my program to many planetlab nodes.

But seeing the setting instruction, it's too inconvenient.

There are too many parameter to set.

So I write a simple ruby script to implement this multiple upload function.

usage: ./multi-upload directly_you_want_to_upload

script:

#! /usr/bin/ruby

arr = IO.readlines("node_list")

arr.each { |x|

puts "node name:#{x.chomp}"

cmd = "scp -r #{ARGV[0]} ACCOUNT@#{x.chomp}:/home/ACCOUNT"

puts `#{cmd}`

}

See, 9 lines code can do the same thing.

Why don't use it?

vim window tips

#define c-w Control + key W

對目前編輯檔案分割視窗:
分割垂直視窗: c-w v
分割水平視窗: c-w s
關閉視窗: c-w q
留下目前視窗並且關閉其他視窗: c-w o
於分割視窗開新檔案: c-w n

切換:
切換到下方視窗: c-w j
切換到上方視窗: c-w k
切換到左方視窗: c-w h
切換到右方視窗: c-w l
切換到下一個視窗:
調整大小
調整視窗垂直大小: c-w [+|-]
調整視窗水平大小: c-w [<|>]