Words In STL(2nd Edition)

07 Jul 2015

Words && Sentences

  • c++ compiler vendor : c++编译器提供商
  • noexcept targets a lot of problems (empty) exceptions specifications have.
    target: 以。。。为目标
  • conservative approach: 保守的方式
  • mandatory: 强制的 [ˈmændətɔ:ri]
    All of them are optional, but if one of them occurs, the parentheses([pə’renθəsi:z]) for parameters are mandatory.

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05 Jul 2015




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working 4 hours everyday

29 Jun 2015

每个人都熟悉这种作息规律:早上9点去上班,坐在电脑前面,编一天的程序,下午5点下班回家。如今,非常感谢蒂莫西·费里斯 (Timothy Ferriss)的《每周工作4小时》,我开始重新思考应该如何工作,如何让自己变成更有效率的程序员。 最近,我把我的从周一到周五的作息规律做了一次较大的调整。很长时间以来,我一直像所有其他程序员那样工作、休息。但就在2011年的下半年,我开 始了一项试验,想看看究竟什么样的作息时间能让我更有效率。这项实验目前仍在进行中,我并不是像军人那样严格遵守实验规定——例如,我也想会早20分钟、 或晚20分钟起床——但当前制定的作息规律是这样的: 早上4:30 到 7 点:冥想,写作,目标复查,和家人吃早餐 ...

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windows skills

18 Mar 2015

1. the system

  • how long the system has run? cmd>systeminfo
  • remote connect win+r : mstsc
  • Turn on Telnet 控制面板 -》程序和功能 -》开启或关闭windows功能 -》telnet客户端

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Linux kernel coding style

18 Mar 2015

Annotation from Chris Lott: This is file ‘CodingStyle’ from the Linux kernel source area. Of course the author is Linus Torvalds. To get the most recent version of this document, see:

	Linux kernel coding style 
This is a short document describing the preferred coding style for the linux kernel. Coding style is very personal, and I won’t force my views on anybody, but this is what goes for anything that I have to be able to maintain, and I’d prefer it for most other things too. Please at least consider the points made here. First off, I’d suggest printing out a copy of the GNU coding standards, and NOT read it. Burn them, it’s a great symbolic gesture. Anyway, here goes:
 	Chapter 1: Indentation
Tabs are 8 characters, and thus indentations are also 8 characters. There are heretic movements that try to make indentations 4 (or even 2!) characters deep, and that is akin to trying to define the value of PI to be 3. Rationale: The whole idea behind indentation is to clearly define where a block of control starts and ends. Especially when you’ve been looking at your screen for 20 straight hours, you’ll find it a lot easier to see how the indentation works if you have large indentations. Now, some people will claim that having 8-character indentations makes the code move too far to the right, and makes it hard to read on a 80-character terminal screen. The answer to that is that if you need more than 3 levels of indentation, you’re screwed anyway, and should fix your program. In short, 8-char indents make things easier to read, and have the added benefit of warning you when you’re nesting your functions too deep. Heed that warning.
	Chapter 2: Placing Braces
The other issue that always comes up in C styling is the placement of braces. Unlike the indent size, there are few technical reasons to choose one placement strategy over the other, but the preferred way, as shown to us by the prophets Kernighan and Ritchie, is to put the opening brace last on the line, and put the closing brace first, thusly:
	if (x is true) {
		we do y
However, there is one special case, namely functions: they have the opening brace at the beginning of the next line, thus:
	int function(int x)
		body of function
Heretic people all over the world have claimed that this inconsistency is … well … inconsistent, but all right-thinking people know that (a) K&R are right and (b) K&R are right. Besides, functions are special anyway (you can’t nest them in C). Note that the closing brace is empty on a line of its own, except in the cases where it is followed by a continuation of the same statement, ie a “while” in a do-statement or an “else” in an if-statement, like this:
	do {
		body of do-loop
	} while (condition);
	if (x == y) {
	} else if (x > y) {
	} else {
Rationale: K&R. Also, note that this brace-placement also minimizes the number of empty (or almost empty) lines, without any loss of readability. Thus, as the supply of new-lines on your screen is not a renewable resource (think 25-line terminal screens here), you have more empty lines to put comments on.
	Chapter 3: Naming
C is a Spartan language, and so should your naming be. Unlike Modula-2 and Pascal programmers, C programmers do not use cute names like ThisVariableIsATemporaryCounter. A C programmer would call that variable “tmp”, which is much easier to write, and not the least more difficult to understand. HOWEVER, while mixed-case names are frowned upon, descriptive names for global variables are a must. To call a global function “foo” is a shooting offense. GLOBAL variables (to be used only if you really need them) need to have descriptive names, as do global functions. If you have a function that counts the number of active users, you should call that “count_active_users()” or similar, you should not call it “cntusr()”. Encoding the type of a function into the name (so-called Hungarian notation) is brain damaged - the compiler knows the types anyway and can check those, and it only confuses the programmer. No wonder MicroSoft makes buggy programs. LOCAL variable names should be short, and to the point. If you have some random integer loop counter, it should probably be called “i”. Calling it “loop_counter” is non-productive, if there is no chance of it being mis-understood. Similarly, “tmp” can be just about any type of variable that is used to hold a temporary value. If you are afraid to mix up your local variable names, you have another problem, which is called the function-growth-hormone-imbalance syndrome. See next chapter.
	Chapter 4: Functions
Functions should be short and sweet, and do just one thing. They should fit on one or two screenfuls of text (the ISO/ANSI screen size is 80x24, as we all know), and do one thing and do that well. The maximum length of a function is inversely proportional to the complexity and indentation level of that function. So, if you have a conceptually simple function that is just one long (but simple) case-statement, where you have to do lots of small things for a lot of different cases, it’s OK to have a longer function. However, if you have a complex function, and you suspect that a less-than-gifted first-year high-school student might not even understand what the function is all about, you should adhere to the maximum limits all the more closely. Use helper functions with descriptive names (you can ask the compiler to in-line them if you think it’s performance-critical, and it will probably do a better job of it that you would have done). Another measure of the function is the number of local variables. They shouldn’t exceed 5-10, or you’re doing something wrong. Re-think the function, and split it into smaller pieces. A human brain can generally easily keep track of about 7 different things, anything more and it gets confused. You know you’re brilliant, but maybe you’d like to understand what you did 2 weeks from now.
	Chapter 5: Commenting
Comments are good, but there is also a danger of over-commenting. NEVER try to explain HOW your code works in a comment: it’s much better to write the code so that the working is obvious, and it’s a waste of time to explain badly written code. Generally, you want your comments to tell WHAT your code does, not HOW. Also, try to avoid putting comments inside a function body: if the function is so complex that you need to separately comment parts of it, you should probably go back to chapter 4 for a while. You can make small comments to note or warn about something particularly clever (or ugly), but try to avoid excess. Instead, put the comments at the head of the function, telling people what it does, and possibly WHY it does it.
	Chapter 6: You've made a mess of it
That’s OK, we all do. You’ve probably been told by your long-time Unix user helper that “GNU emacs” automatically formats the C sources for you, and you’ve noticed that yes, it does do that, but the defaults it uses are less than desirable (in fact, they are worse than random typing - a infinite number of monkeys typing into GNU emacs would never make a good program). So, you can either get rid of GNU emacs, or change it to use saner values. To do the latter, you can stick the following in your .emacs file:
(defun linux-c-mode ()
  "C mode with adjusted defaults for use with the Linux kernel."
  (c-set-style "K&R")
  (setq c-basic-offset 8))
This will define the M-x linux-c-mode command. When hacking on a module, if you put the string -- linux-c -- somewhere on the first two lines, this mode will be automatically invoked. Also, you may want to add
(setq auto-mode-alist (cons '("/usr/src/linux.*/.*\\.[ch]$" . linux-c-mode)
to your .emacs file if you want to have linux-c-mode switched on automagically when you edit source files under /usr/src/linux. But even if you fail in getting emacs to do sane formatting, not everything is lost: use “indent”. Now, again, GNU indent has the same brain dead settings that GNU emacs has, which is why you need to give it a few command line options. However, that’s not too bad, because even the makers of GNU indent recognize the authority of K&R (the GNU people aren’t evil, they are just severely misguided in this matter), so you just give indent the options “-kr -i8” (stands for “K&R, 8 character indents”). “indent” has a lot of options, and especially when it comes to comment re-formatting you may want to take a look at the manual page. But remember: “indent” is not a fix for bad programming.
	Chapter 7: Configuration-files
For configuration options (arch/xxx/, and all the files), somewhat different indentation is used. An indention level of 3 is used in the code, while the text in the config- options should have an indention-level of 2 to indicate dependencies. The latter only applies to bool/tristate options. For other options, just use common sense. An example:
if [ "$CONFIG_EXPERIMENTAL" = "y" ]; then
   tristate 'Apply nitroglycerine inside the keyboard (DANGEROUS)' CONFIG_BOOM
   if [ "$CONFIG_BOOM" != "n" ]; then
      bool '  Output nice messages when you explode' CONFIG_CHEER
Generally, CONFIG_EXPERIMENTAL should surround all options not considered stable. All options that are known to trash data (experimental write- support for file-systems, for instance) should be denoted (DANGEROUS), other Experimental options should be denoted (EXPERIMENTAL).
	Chapter 8: Data structures
Data structures that have visibility outside the single-threaded environment they are created and destroyed in should always have reference counts. In the kernel, garbage collection doesn’t exist (and outside the kernel garbage collection is slow and inefficient), which means that you absolutely have to reference count all your uses. Reference counting means that you can avoid locking, and allows multiple users to have access to the data structure in parallel - and not having to worry about the structure suddenly going away from under them just because they slept or did something else for a while. Note that locking is not a replacement for reference counting. Locking is used to keep data structures coherent, while reference counting is a memory management technique. Usually both are needed, and they are not to be confused with each other. Many data structures can indeed have two levels of reference counting, when there are users of different “classes”. The subclass count counts the number of subclass users, and decrements the global count just once when the subclass count goes to zero. Examples of this kind of “multi-reference-counting” can be found in memory management (“struct mm_struct”: mm_users and mm_count), and in filesystem code (“struct super_block”: s_count and s_active). Remember: if another thread can find your data structure, and you don’t have a reference count on it, you almost certainly have a bug. ...

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