August 2018
Beginner to intermediate
382 pages
7h 14m
Chinese
Content preview from Perl语言入门
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32
｜
第
2
章
比如：
1.25
255.000
255.0
7.25e45 # 7.25
乘以
10
的
45
次方（一个非常大的数）
-6.5e24 #
负
6.5
乘以
10
的
24
次方
#
（一个非常大的负数）
-12e-24 #
负
12
乘以
10
的
-24
次方
#
（一个非常小的负数）
-1.2E-23 #
另一个种写法，
E
换做大写
Perl 5.22
新增了十六进制浮点数直接量的写法。
和用
e
表示以
10
为幂的写法类似，
用
p
表示以
2
为幂。和十六进制整型数字一样，以
0x
开头：
0x1f.0p3
十六进制的浮点数直接量其实就是
Perl
内部保存数字时所使用的形式。所以就取值大
小来说，完全不存在转换带来的近似问题。如果用十进制表示，
Perl
（或
C
语言，或
其他使用双精度的语言）则无法完全精确表示以
2
为幂的数字。可能大部分人从未关
注过这个细节，但因此产生的进位舍入（
round-off
）带来的计算偏差一直困惑着相当
一部分人。通过这种写法我们能够自然规避这个问题。
数字操作符
操作符相当于语言中的动词。操作符决定了处理名词的方式。
Perl
提供各种常见的运
算操作符，加减乘除一个不少，我们用相应的字符来表示这些运算符号。数字操作符
总是把处理对象看作数字：
2 + 3 # 2
加
3
，得
5
5.1 - 2.4 # 5.1
减
2.4
，得
2.7
3 * 12 # 3
乘以
12
，得
36
14 / 2 # 14
除以
2
，得
7
10.2 ...
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