Simple understanding of interpreters and compilers

About the difference between compiler and interpreter - EYES Group - Blog Garden (cnblogs.com)https://www.cnblogs.com/130701-EYES/p/5301555.htmlzz from http://www.cppblog.com/pengkuny/articles/23106.html

Cattle farm of Laifu and Wangcai

Laifu and Wangcai have one support Cattle farm . It was not too difficult to raise cattle , But their cows have special quirks . A yuan cow only eats grass cut into circles , And cow a Fang and a San （ From India ？） Eat separately and cut into squares And triangular grasses . If Laifu and Wangcai take grass that is not consistent with the cow's character to feed , o X They not only do not produce milk, but also despise Laifu and Wangcai .

So Laifu and Wangcai had their own ideas

Laifu's plan ：
Laifu invented three sets of large crushers ： Round crusher , Fangfang crusher and Sansan crusher . Grass is harvested every day , Put them into these three sets of machines and grind them for three cows . But once crushed , This pile of grass can only be eaten by a certain cow . Obviously, Afghanistan will not eat the grass prepared for ah yuan . And Laifu operates these three machines every day , I think it's troublesome .
 

Wangcai's plan ：
Wangcai inspected the plan of Laifu , I found it really troublesome to operate three machines every day , And sometimes some cows can't finish , When some cows are not enough to eat , You can't mix crushed grass among cows . So Wangcai has different ideas ： Mask type crusher .
 

As you can see in the picture , Wangcai equipped each cow with a mask crusher , So three cows can eat grass in one trough , Before eating, the mask will automatically crush the grass into a type suitable for the cow . Wangcai is easy , He only needs to mow the grass every day .

But Wangcai is despised ？？？

Yes , Be despised by Laifu . After observation, Laifu found , The efficiency of Wangcai's mask crusher is very low （ Because it's relatively small ）. A yuan eats a lot , You'll be full in an hour after eating the food of Laifu's round crusher , But it takes ten hours to eat with a mask on ！ So Laifu thinks that Wangcai's mask crusher is easy , But you can only feed calves , It's not suitable for cattle that eat a lot .

Wangcai also thinks it's a problem , But he doesn't want to go back to the Laifu plan , He improved the mask scheme ： Forage pre cutter .
 

ha-ha , See what the pre cutting has done ？ It cuts the grass smaller , Therefore, the need for a mask crusher to do much less .（ Of course, the mask crusher should also be properly improved to suit the pre cut forage , So it is shown in blue ） A yuan used to eat masks for ten hours , Now it will take twoorthree hours .

Compiler and interpreter

well , Thank you for your patience to see here , After the above inappropriate example , I believe you have been quite confused . So let's try to go back to technology .
In the example above
forage grass ＝ Our various programming languages ,C/C++/C#, Java, Pascal, PHP, Python, Perl, Java Script wait
cutting machine ＝ Various compilers
cow ＝ Various CPU（ Don't tell me Intel and AMD Oh ）, such as x86,ARM,MIPS wait
Then you should know why cows have a hobby of eating different shapes of grass , This strange metaphor is to express different CPU Accept different machine languages .

Corresponding to the cow diagram above , The diagram of the compiler is like this

 

The source code is compiled into machine code , stay CPU Up operation .

The interpreter is like this
 

Using the interpreter is very convenient , Just direct “ function ” Just fine , Don't look like C That way, there is the process of compiling links .

Why are these languages cross platform ？ Because after you write the program , If there is an interpreter of this language on this platform , Just get it and run it directly on this platform . You can understand it as ： The interpreter is in “ While compiling , While running ”, It just puts the compilation process manually done by programmers before when running the program .

Why do we generally say that the efficiency of the interpreter is relatively low ？ You can also imagine , A program may be compiled many times when it runs in the interpreter , Because every time you run this program , Will be recompiled , This kind of expense is very big .

So was born Java,C# Such a precompiled language ：
 

Before running , You need to manually compile the source code into intermediate code （Java It's called bytecode ）, Then execute it in the interpreter .
This architecture avoids the overhead of compiling source code in the pure interpreter above , So it will be relatively efficient .

But I can't lie to you , Actually, I drew it in the pure interpreter Python,Perl,PHP It may not be really pure interpretation execution , This is really inefficient .Python It will generate become pyc Binary temporary file , It looks like the result of precompiling . Only JavaScript This really will not write too long language （Ajax Please forgive me ） Will adopt the pure interpretation of the operator type .