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C++ revisit


I liked C programming, as it is low level and the compiler is widely available. Using C language can demonstrate the understanding of pointer and memory. You can implement a linked list or a hash table by using C. So that you can understand better how the linked list and hash table work.

But as long as you want to build some end user applications, C language is never a good choice. Choosing a language for our product is important. We do not develop a web application using low level programming language. It is totally impractical.

C and C++

Do not think that C language is an old language. It can survive until today because it has some powerful features (yet I cannot name them out, because I am not a C developer). There are new features on C99 and C11. But practically to solve higher level problem like game development, C++ is much more better than C. (But there is a better choice like Lua.)

Syntax

Why is C++ better than C? From the syntax level, it is easier to read and easier to write. For example,

strtolower(trim(myString));

where myString is a C string, then trim() is a function that returns trimmed string, strtolower() is another function that returns the string with lower case. (The function names I used here is based on PHP.) So, we can see, when we read or write, we need to read from right to left: trim then strtolower. And the parentheses needs to be matched properly.

On the other hand for C++,

myString->trim()->strtolower();

Let’s say myString is a customized object, namely MyString, that manipulates the string. So, the syntax is much more intuitive. myString calls the trim() method and returns the MyString object, so that we can continue with strtolower() that returns MyString object. This is called method chaining.

Object oriented

Object oriented is a wondrous invention! It is so powerful that most programming languages today support object oriented. Inheritance, polymorphoism, and interface, these features reduce a lot of tremendous works. You can implement object oriented in C (using library such as GObject), but C language is not designed for object oriented.

Because of syntax and the object oriented, I prefer C++ than C.

String

Another advantage of C++ is the string. C string is an array of character, with the fixed size. It is not dynamic as C++ string. For example, you want to perform strcat(), you need to have a larger buffer to store the strcat() result. And if you want to do it with dynamic memory allocation, then you have to free the memory manually. This is exhaustive.

Object method

Related to method chaining, in C++ we can write the methods. In C, because it is using struct, to implement something like method is troublesome. For example,

#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int a;
    int (*b)(int a);
} MyType;

int myTypeMethod(int a) {
    return a+20;
}

MyType* myTypeNew() {
    MyType* myType = (MyType*)malloc(sizeof(MyType));
    myType->a = 20;
    myType->b = myTypeMethod; //There is no method in struct, so we assign the callback function
    return myType;
}

void myTypeDelete(MyType** myType) {
    free(*myType);
    *myType = NULL;
}

int main(int argc, char** argv) {
    MyType* myType = myTypeNew();
    printf("%d\n", myType->a);
    printf("%d\n", myType->b(20));
    myTypeDelete(&myType);
    return 0;
}

Because C doesn’t have namespace, but we can do something like namespace by using prefix.

C++11, C++14, C++1z

If you are not C++ lover, you may think that C++ is an archaic programming language. Just like HTML and JavaScript, there are ongoing proposals for the new features for C++. That is why, C++ is not dying yet. There are some notable features I need to state here.

New syntax

“auto” data type

#include <iostream>
#include <typeinfo>
using namespace std;

int main(int argc, char** argv) {
  int a = 10;
  auto b = a;
  cout << b << endl;
  cout << typeid(b).name() << endl; //"i" as integer
  float c = 20.0f;
  b = c;
  cout << b << endl;
  cout << typeid(b).name() << endl; //Still "i"
  return 0;
}

“auto” is just like “var” in C#.

foreach

Most modern programming languages allows foreach keyword, like JavaScript, PHP, and even Python. Though Python uses “for” keyword, it works actually like foreach in PHP.

#include <iostream>
using namespace std;
int main(int argc, char** argv) {
  int a[] = { 4, 5, 3, 2, 1 };
  for(auto item : a) {
    cout << item << endl;
  }
  return 0;
}

Another foreach,

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main(int argc, char** argv) {
  vector<int> a{ 4, 5, 3, 2, 1 };
  for_each(a.begin(), a.end(), [](auto &item) {
      cout << item << endl;
    });
  return 0;
}

The above code can only be compiled with c++14 standard. If using c++11 standard, we must use “int” instead of “auto”.

Lambda expression

Lambda expression, a.k.a anonymous function. If you are working with JavaScript, such as

var a = [ 4, 5, 3, 2, 1 ];
var found = a.find(function(item) {
    if(item == 2)
        return item;
});

So, the above example shows that the parameter of the find() is a function, without a function name. This is a common syntax in functional programming. Functional programming is a trend of most modern programming language. The anonymous function is also supported by PHP. The advantage of functional programming is the elimination of side effects and avoiding changing state of the data. Therefore, it is a good paradigm for parallel programming.

Therefore, looking at the example above, there is some syntax like,

  ([](int b) {
    cout << b << endl;
  })(12);

Which is similar to JavaScript,

(function(b) {
    console.log(b);
})(12);

In C++, the squared bracket is used to capture the variable of the scope. (I think it is similar to PHP “using” keyword.)

Previously, we can use the callback function like,

#include <iostream>
using namespace std;

int foo(int (*cb)(int, void*), int size, void* data) {
  return cb(size, data);
}

int callback(int size, void* data) {
  int sum = 0;
  int* intData = (int*)data; //typecast
  for(int i=0;i<size;i++) {
    sum += intData[i];
    cout << intData[i] << endl;
  }
  return sum;
}

int main(int argc, char** argv) {
  int a[] = { 4, 5, 3, 2, 1 };
  int sum = foo(callback, 5, a);
  cout << sum << endl;
  return 0;
}

Since we can use anonymous function, we need not to create a callback function like above. This can be written as,

#include <iostream>
using namespace std;

int foo(int (*cb)(int, void*), int size, void* data) {
  return cb(size, data);
}

int main(int argc, char** argv) {
  int a[] = { 4, 5, 3, 2, 1 };
  int result = foo([](int size, void* data) {
      int sum = 0;
      int* intData = (int*)data;
      for(int i=0;i<size;i++) {
        sum+= intData[i];
        cout << intData[i] << endl;
      }
      return sum;
    }, 5, a);
  cout << result << endl;
  return 0;
}

Multi-threading, asynchronous programming, promise

We can implement multi-threading using other libraries like pthread. But with C++11, you can create thread without third party libraries, perform sleep, sleep by milliseconds or even nanoseconds. There is also library for mutex (mutually exclusive).

C++11 also supports asynchronous programming like C# and promise like JavaScript. With the lambda expression, the syntax shares some similarities with C# and JavaScript. With async, we can do something at the background (using thread), and use the result later. With promise, you can promise to return some value, else throw an exception.

Regular expression

Regular expression is so important for text processing. C++11 supports regular expression. There are different regular expression syntax: BRE (basic regular expression) is the default syntax used by “grep” command, ERE (extended regular expression, and Perl regular expression. Perl regular expression is very powerful. If you use Python, JavaScript, Ruby, and C#, you will find that they have different syntax.

However, interestingly C++ uses ECMAScript regular expression syntax by default (though we can choose BRE, ERE, or awk). That means, if you know JavaScript RegExp, then you will have no problem with C++ regex.

(I see the converging features of the different programming languages, which means these features are useful, intuitive, and influential.)

 

Garbage collection

So far, there is no good garbage collection for C++.

 

Another thing I have to state. Because of the networking and big data, parallel programming is a demand and the trend. To make sure the data is immutable, functional programming becomes handy.

Openbox + tint2


Previously I was using Xfce4. Then, because of the heavy working environment, I tried the lighter desktop environment, LXDE. But still, it has some limitations that made me choose to use Openbox window manager only.

Pros and cons of Xfce4

Xfce4 is lightweight comparing to GNOME or KDE. I like it, because of the conventional design like the task manager. Furthermore another thing I like is the “aerosnap” feature like Windows, which I can view the two windows side by side. However, when running Windows in VirtualBox and other applications, I can feel the obvious slowness in the computer. It is really reducing my working performance. That is why I decided to change to LXDE.

Pros and cons of LXDE

LXDE is lighter than Xfce4. So, running a lot of heavy applications does not slow down the computer like Xfce4. But there was one issue I faced. The LXDE pager (workspace) does not allow me to drag and drop the applications to move among the workspaces.

As a result, I decided to use something lighter than Xfce4 and I can drag and drop the applications among the workspaces easily.

Openbox and tint2

I had experienced Openbox with tint2 when I was using my old laptop. Openbox is nice and highly customisable. Tint2 allows me to set number of workspaces, and easily to move the applications to other workspaces. However, tint2 does not have applets or plugins like Xfce4 or LXDE.

There is one feature I need, that is to see CPU usage, so that I know whether there is any application causes high CPU usage. As a result, I installed Conky and display the CPU usage at the corner of the desktop.

Openbox + tint2

Openbox + tint2

Conky

For the Conky, the following is the conky.conf

conky.config = {
    alignment = 'bottom_right',
    background = false,
    border_width = 0,
    cpu_avg_samples = 2,
	default_color = 'white',
    default_outline_color = 'BBBBBB',
    default_shade_color = '444444',
    draw_borders = false,
    draw_graph_borders = false,
    draw_outline = false,
    draw_shades = false,
    use_xft = true,
    font = 'DejaVu Sans Mono:size=1', --by size 1 then only there will have no space after cpugraph
    gap_x = 0,
    gap_y = 2,
    minimum_height = 5,
	minimum_width = 5,
    net_avg_samples = 2,
    no_buffers = true,
    out_to_console = false,
    out_to_stderr = false,
    extra_newline = false,
    own_window = true,
    own_window_class = 'Conky',
    own_window_type = 'desktop',
	own_window_transparent = true,
	own_window_argb_visual = true,
	own_window_argb_value = 255,
    stippled_borders = 0,
    update_interval = 1.0,
    uppercase = false,
    use_spacer = 'none',
    show_graph_scale = false,
    show_graph_range = false,
	double_buffer = true,
	imlib_cache_size = 10,
}

conky.text = [[
	${cpugraph 27,40 000000 FFFFFF -l}
]]

Cloud9


Cloud9 is a web-based IDE good for collaboration and online development. You can store your large project on the remote server, and use any computer including netbook with a web browser to develop your system.

Now, the problem I faced when using C9 on my Chromium. Firstly, the address bar, tabs, and bookmarks occupy some space in the window. This results a non-editor look and feel. This makes me feel lacking of something. Secondly, the worst part is the shortcut key like Ctrl+W. By pressing this shortcut key, it will invoke the web browser closing window instead of the C9 shortcut key. Meaning, the shortcut key of the web browser has higher precedence than C9 itself.

I looked for the C9 official Chrome extension, namely Cloud9, but it just works like a bookmark. I tried also Cloud 9 IDE Shortcut. It works better than official Cloud9 Chrome extension. Yet, I need to enter my username and password for the first time. Another drawback is the missing of the window icons like minimize, maximize/restore, and close, and title bar, which results difficulty to resize and maximize/restore.

Looks for some solutions. The easiest way is to invoke

chromium --app=https://ide.c9.io/

Yay! Now I can use the shortcut keys and it looks like native text editor!

Chromium running C9 as app

Chromium running C9 as app

If you are serious, you can write the manifest.json to create the C9 web app, then you can have a custom icon instead of Chromium icon.

Vim


Because of the new working environment, I cannot use my favourite customised Emacs to work. So, I have to adapt with the new text editor. Luckily, vim is available in the remote server. That means I can use SSH to run the vim. And, even Emacs is available, I feel difficult to customise and install the packages I need, because I don’t have experience installing Emacs’ packages using text-based UI. (But if it is available, I may make a try.)

On the other hand, vim is a little different. vim is more tend to text-based UI, though there is a GUI version called GVim. In order to familiarise with vim, I also did some customisation on it, especially the key binding (hotkey) which is, totally not user-friendly by default. So, I share my ~/.vimrc with this post.

:set tabstop=4 ai ic wrap lbr showcmd
:set shiftwidth=4
:set expandtab
:set autoread
:set list
:set listchars=eol:↵,tab:→·,space:⋅
:set whichwrap+=<,>,h,l,[,]
":set nu
:set display+=lastline
:colorscheme ron

:filetype plugin on
:syntax on

"Navigate
vmap <Down> gj
vmap <Up> gk

"This will be overridden by YouCompleteMe, so need to have alternave solution
imap <Down> <C-o>gj
imap <Up> <C-o>gk
imap <C-Down> <C-o>gj
imap <C-Up> <C-o>gk
nmap <Down> gj
nmap <Up> gk

"Select
nmap <S-Up> v<Up>
nmap <S-Down> v<Down>
nmap <S-Left> v<Left>
nmap <S-Right> v<Right>
nmap <S-Home> v<Home>
nmap <S-End> v<End>
imap <S-Up> <C-o>v<Up>
imap <S-Down> <C-o>v<Down>
imap <S-Left> <C-o>v<Left>
imap <S-Right> <C-o>v<Right>
imap <S-Home> <C-o>v<Home>
imap <S-End> <C-o>v<End>
vmap <S-Up> <Up>
vmap <S-Down> <Down>
vmap <S-Left> <Left>
vmap <S-Right> <Right>
vmap <S-Home> <Home>
vmap <S-End> <End>

"Remap the delete key, so that will not override the register for pasting
vmap <Delete> "_x
vmap <Backspace> "_x

"For the characters like newline (if shown with list)
highlight NonText guifg=#333333 guibg=#000000 ctermfg=darkgrey
"For special key like whitespace and tab
highlight SpecialKey guifg=#333333 guibg=#000000 ctermfg=darkgrey

 

GVim and Emacs

Best ever text editors: (g)vim and emacs

External HDD struggling


I have an HP 1T external HDD. It is dying. Sh*t!

So, I made my final struggling onto it. Though it is not 100% work as planned, I still have around 320G usable space.

Symptoms

Firstly, I found that some files cannot be deleted, I had no choice but plug out the USB cable manually. Try to chkdsk with Windows since it is NTFS partition, but the chkdsk stopped and no response during the progress. Then I know, these were the bad signs. So, have to avoid using it and get a new HDD, and move whatever files able to be moved.

Backup like sh*t

I use Linux instead of Windows, because copying out the files with Windows is damn slow. So, I have no choice but to use Linux. During copying from this pity HDD to the new HDD, the copying process will stop without warning, and the HDD failed to work. Worst, there was no way to cancel the operation, only solution to plug it out. I repeated this procedure approximately 60-70 times (heuristic guess only).

S.M.A.R.T

There is one thing I have to mention, that is S.M.A.R.T. I had enabled it on the external HDD, but it did not show any useful feature to SAVE my date.

NTFS

After copying out primary data and giving up some secondary data, I decided to re-format it as NTFS. Though I very dislike Windows, NTFS is still the main stream. NTFS and FAT32 are widely supported by the devices, for instance, LG video player. I also considered exFAT, but it is not as good as NTFS supported by Linux.

So, booted into Windows, plugged in the USB cable, format the disk without “Quick Format”, because I intended to have a thorough “chkdsk” scanning for bad sector.

Unfortunately, it was DAMN slow. To increase from 0% to 1% requires about 30 minutes. How am I going to live my following life?

Then I cancelled the format and gave up NTFS.

ext4

Since there was no more hope on NTFS, I planned to format as ext4. I run mkfs.ext4 with “-c” to check for bad blocks (something like bad sectors). But it failed. The hard disk failed to work until I re-plugged in the USB. I tried dmesg, found that there are a lot of errors like

usb 2-2: reset SuperSpeed USB device number 2 using xhci_hcd
usb 2-2: LPM exit latency is zeroed, disabling LPM.
blk_update_request: I/O error, dev sdb, sector 721688448

I concluded that it is not just bad sectors/blocks, but just failed to read the blocks.

badblocks

So, I assumed that mkfs.ext4 with “-c” or even fsck.ext4 will not solve my problem. Those bad sectors should never be accessed. So, I decided to give up those sectors, meaning, skip those factors from the partitions. This can be done by using fdisk or cfdisk, creating the partitions based on the “sector” unit instead of size. We can create the partition to occupy the bad sectors area, then create next partition after it, and then delete the partition that has bad sectors.

Then, the next question is how to find the bad sectors. mkfs.ext4 and fsck.ext4 cannot solve, because they are checking for the bad sectors thoroughly through the partition. The solution is to use “badblocks”.

There are two things have to know, i) sector and ii) block. They are different things. badblocks command can identify the bad blocks, but not the bad sectors. However, fdisk allows us to get the total number of the sectors.

Now, we can do some maths here. Let’s say you run the “fdisk -l”, and get this,

Disk /dev/sdb: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors

The total number of the sectors of the hard disk is 1953525168.

Now, to get the total number of blocks, use “cat /proc/partitions”, you will get something like this,

major minor  #blocks  name

   8        0  976762584 sdb

So, that is the total number of blocks, 976762584. And you can do the calculation, 976762584*2 = 1953525168. So, 1 block = 2 sectors.

This is important information, because when we use the badblocks, the values are shown in block unit. But when we want to create partitions, we are using sector unit.

So, when we run the badblocks like

badblocks -v -s -o bad.txt /dev/sdb

It will show something like

Checking blocks 0 to 976762583

which is the first block (0) until the last block (976762584 -1).

Now, in case we stop/interrupt the badblocks, we can continue from any where we want. Or, we can just start from any block. For instance

badblocks -v -s -o bad.txt /dev/sdb 976762583 488381292

where the 976762583 is the last block we want to check, and 488381292 is the start block we want to check. (Please read the manual in detail.)

Result

So, based on these tools and information, finally I found that there is around 320G contiguous safe space. So, I create the partition for it, and finally format it at ext4. Since it is a dying hard disk, I will not use it to store primary data, but secondary data and secondary backup. (Secondary data is unimportant; secondary backup is the duplicated backup, not one and only one.)

Actual plan for the next stage

Unfortunately, because the hard disk has critical failure, I cannot implement the next stage.

In my expectation, the hard disk may have multiple large, contiguous, and safe space. For example, 0-25% from the beginning is safe, and 60-100% is safe. As a result, I can create 2 partitions for these space. This is what I actually want. If this really happen, then I can use the LVM so that I can combine both partitions as a logical volume, and finally mkfs on it.

But since it does not happen, I cannot test on the LVM.

 

Search song that plays on your computer (Linux)

Posted on

Since I am working as freelance developer, I spent most of my “otaku” time with Animenfo Radio. Now, when listening with some nice songs you like, and you would like to know what the song is, then you can use Shazam to detect it. But using Shazam requires you to turn on your volume and use your mobile phone to detect it.

What if, you are listening the songs with your ear-phone?

To make it work on your Linux computer,

  1. Listen to a music or song, make sure it is still playing
  2. Run pavucontrol (PulseAudio Volume Control), install it if you didn’t
  3. Open a music searching website such as Midomi (so far I only know this website)
  4. Click the recording button (make sure it starts recording), allow using microphone as prompted by the web browser
  5. Then you will see this in pavucontrol
  6. PulseAudio Volume Controller record audio

    PulseAudio Volume Controller record audio

  7. There are two options, one is “Built-in Audio Analog Stereo”, another is “Monitor of Built-in Audio Analog Stereo”. Choose the “Monitor” something will redirect your computer audio output to your computer recorder (input).
  8. Then, the website like Midomi will get what you are listening, and submit for a search!

Yeah! No Shazam, and you can search when you are listening with the ear-phone.

Windows – Linux Edition (opinion only)

Posted on

This is just an opinion, not the fact.

Not long ago, there is an announcement that Windows can run Bash on Ubuntu on Windows. Not only that, there is Windows subsystem for Linux.

Surely, Linux and UNIX have a lot of powerful features, especially developer oriented. That is why Windows has to adopt them. Because they really solves a lot of problems, such as bash and other commands like grep, find, and vi. Cloud computing is emerging, command-line is much more efficient than GUI. Text file for collaborative development is much more efficient (using git) than working on binary file, as you cannot diff and patch.

Since Windows now supports Linux subsystem, in my opinion, Windows may come out Windows – Linux Edition that

  • uses the UNIX filesystem hierarchy standard
  • supports commercial device drivers (like printers)
  • supports Linux container virtualisation
  • can run Windows applications natively (without WINE)
  • run X window customised with Windows theme
  • uses its own package manager with package repository
  • is cheaper price

I believe, there will be a group of users interested in it!

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