PHP下对字符串的递增运算代码

PHP 2018-12-30

有同学问了一个问题:
<div class="codetitle"><a style="CURSOR: pointer" data="44974" class="copybut" id="copybut44974" onclick="doCopy('code44974')"> 代码如下:

<div class="codebody" id="code44974">
<?php
for($i = 'A'; $i <= 'Z'; $i++) {
echo $i;
}
//输出是啥?

输出是:
<div class="codetitle"><a style="CURSOR: pointer" data="36688" class="copybut" id="copybut36688" onclick="doCopy('code36688')"> 代码如下:

<div class="codebody" id="code36688">
ABCDEFGHIJKLMNOPQRSTUVWXYZAAABACADAEAFAGAHAIAJAKALAMANAOAPAQARAS…….

为啥? 其实很简单,PHP的手册中也有说明,只不过恐怕很多人不会一章一节的把手册仔细阅读一遍:
<div class="codetitle"><a style="CURSOR: pointer" data="14662" class="copybut" id="copybut14662" onclick="doCopy('code14662')"> 代码如下:

<div class="codebody" id="code14662">
PHP follows Perl's convention when dealing with arithmetic operations on character variables and not C's. For example,in Perl ‘Z'+1 turns into ‘AA',while in C ‘Z'+1 turns into ‘[‘ ( ord(‘Z') == 90,ord(‘[‘) == 91 ). Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

在处理字符变量的算数运算时，PHP 沿袭了 Perl 的习惯，而非 C 的。例如，在 Perl 中 ‘Z'+1 将得到 ‘AA'，而在 C 中，'Z'+1 将得到 ‘[‘（ord(‘Z') == 90，ord(‘[‘) == 91）。注意字符变量只能递增，不能递减，并且只支持纯字母（a-z 和 A-Z）。也就是说,如果:
<div class="codetitle"><a style="CURSOR: pointer" data="54183" class="copybut" id="copybut54183" onclick="doCopy('code54183')"> 代码如下:<div class="codebody" id="code54183">
$name = "laruence";
++$name; //将会是"laruencf"

而:
<div class="codetitle"><a style="CURSOR: pointer" data="35620" class="copybut" id="copybut35620" onclick="doCopy('code35620')"> 代码如下:<div class="codebody" id="code35620">
$name = "laruence";
--$name; //没有影响,还是"laruence"

所以,这个问题的原因就是当$i = Z的时候,++$i成了AA,而字符串比较的话,
AA,BB,XX一直到YZ都是小于等于Z的… so.. 作者: laruence

字符串字符串递增运算

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