January 2021
Intermediate to advanced
505 pages
9h 45m
Chinese
Content preview from PHP编程：第4版
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44
｜
第
2
章
语言基础
左移位（
<<
）
左移位操作符将左边二进制表示的操作数中的位向左移动
N
次，
N
为右边操作数的
值。两个操作数如果不是整数会首先被转换成整数。每次移动，所有的二进制数字
都向左移动一位，同时最右边用
0
补充。例如，
3<<1
（或者二进制数
11
左移一位），
结果变为
6
（二进制数为
110
）。
每次向左移动一位，左边操作数都增加一倍。左移的操作等于左边的操作数乘以
2
的
N
次幂，
N
等于右边操作数的值。
右移位（
>>
）
右移位操作符将左边二进制表示的操作数中的位向右移动
N
次，
N
为右边操作数的
值。两个操作数如果不是整数会首先被转换成整数。每次右移一个正二进制数时，
最左边补
0
作为数字的最左位，并将所有其他位右移一位。把一个负二进制数右移时，
将在它最左边插入
1
作为数字的最左位，并将所有其他位右移一位。例如，
13>>1
（或
者二进制
1101
）右移一位，结果变为
6
（二进制数为
110
）。
逻辑操作符
逻辑操作符提供了创建复杂逻辑表达式的方法。逻辑操作符把它的操作数当成布尔变量，
并且返回一个布尔结果。逻辑操作符包括标点和英文单词两种形式（
||
或者
or
代表同
一种操作符）。逻辑操作符有如下几种。
逻辑与（
&&
，
and
）
当两个操作数都为真时，逻辑与操作符的结果为
true
，否则为
false
。如果第一个
操作数是
false
，逻辑与操作符就知道结果也一定为
false
，所以右边的操作数就不
会被执行了，这种处理过程叫作
短路
（
short-circuiting
）处理。
PHP
中常用这种方法
来确保一段代码在某些条件为真时才可以执行。例如，要在某些条件不是 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.