《Programming from the Ground Up》阅读笔记：p217-p238

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《Programming from the Ground Up》学习第11天，p217-p238总结，总计22页。

一、技术总结

1.C compiling

p216, C compiling is split into two stages - the preprocessor and the main compiler。

注：感觉这个写法不好，因为preprocessor和compiler都是对象，这里应该指动作。应该是：C compiling is split into two stages - the preprocessing and compilation。

(1)preprocessing

p216, The preprocessor is responsible for putting together the text of the program.

从代码上来说，通过#include <stdio.h>指令实现。

(2)compilation

#include <stdio.h>：尖括号(angle bracket)包含的内容一般会到/usr/include或者/usr/local/include路径下寻找(如：stdio.h)。

#include “stdio.h”：引号(quote)包含的内容一般会到当前目录(current directory)下寻找。

2.Perl

Perl是一种解释型语言。

#!/usr/bin/perl
 
print("Hello Perl!\n");

Perl语言的优点是“ In fact, one of Perl’s main strengths is it’s ability and speed at manipulating text.”。

3.Python

Python是一种解释型语言。

#!/usr/bin/python
# filename: helloworld.py

print("Hello Python!")

以前总是不理解 #!/usr/bin/python的作用是什么，看到这里终于理解了。

当我们以 ./helloworld.py 的方式执行helloworld.py程序的时候， #!告诉电脑这是一个interpreted program, 使用/usr/bin/python(即/usr/bin目录下的python)这个interpretor来interprete helloworld.py程序。

当我们以 python helloworld.py 方式来执行helloworld.py程序时，已经显示指定了interpretor,此时#!/usr/bin/python会被忽略掉。

以前对这句话总是不理解，大概是因为头脑中没有interpretor这个概念，其实/usr/bin/下的python就是一个interpretor。

4.optimization(代码优化)

代码优化可以细分为speed, memory space usage, disk space usage等优化。书中讲的主要是speed优化。

(1)when

p234, Therefore, the time to optimize is toward the end of development, when you have determined that your correct code actually has performance problems.

因此，我们往往在开发即将结束时进行优化，这时已经确定代码的正确性，也确定了代码确实存在性能问题。

(2)where

p234, A profiler(性能分析器) is a program that will let you run you program, and it will tell you how much time is spent in each function, and how many times they are run.

a.local

b.global

二、英语总结

1.stick

p217, This includes sticking different files together, running macros on your program text, etc.

vt. to cause sth to become fixed, for example with glue or another similar substance.

2.legwork

p219, You can see that interpreted languages are often focused on letting you get working code as quickly as possible, withou having to do a lot of extra legwork.

也写作leg-work，u.the boring work that need to be done。Originally news reporter slang for an assignment that promised(这里不是“承诺”的意思，而是“很可能(to seem likely)”) more walking than copy.