October 2022
Beginner to intermediate
390 pages
7h 5m
Chinese
Content preview from Perl语言入门（第8版）
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26
｜
第
1
章
我该如何编译
Perl
程序？
只需要直接运行它就可以了。只此一步，
perl
解释器能一次完成编译和运行这两个
动作：
$
perl my_program
运行程序时，
Perl
内部的编译器会先载入整个源程序，将之转换成内部使用的
bytecodes
（字节码），这是一种
Perl
在内部用来表示程序语法树的数据结构。然后
交给
Perl
的字节码引擎执行。所以，如果在第
200
行有个语法错误，那么在开始运行
第二行代码之前，
Perl
就会报告这个错误。如果你的程序中有一个运行
5 000
次的循
环，它只会被编译一次，然后每次循环都以最快的速度运行。除此之外，为了提高易
读性，不论你用多少注释和空白，它们都不会影响运行时（
runtime
）的速度。你甚至
可以使用完全由常量组成的算式，它的值只会在程序开始时被计算一次，哪怕它是在
某个循环中，也只被计算一次，然后在后续的执行中复用计算结果。
不用说，编译是要花时间的——所以如果只是为了迅捷地完成某个简短任务而去运行
一个冗长的包含其他各种任务代码的
Perl
程序，会显得效率低下，因为花在编译上的
时间可能会比运行时间还要长。不过
Perl
编译器的运行速度非常快，通常编译时间只
占运行时间的极少部分而已。
要是把编译后的字节码存储起来，能否节省编译时间？或者更进一步说，能否将字节
码转换成另一种语言，比如
C
语言，然后再进行编译？好吧，其实以上两种做法在某
些情况下都是可行的，不过老实说这么做并没什么好处，程序不会因此变得更易于使
用、维护、调试或安装，甚至（由于某些技术性因素）还会让程序运行得更慢。 ...
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