为什么此代码不简单地将字母A打印到Z?

问题描述

<?php
for ($i = 'a'; $i <= 'z'; $i++)
    echo "$i\n";

此代码段提供以下输出(换行符替换为空格):

This snippet gives the following output (newlines are replaced by spaces):

推荐答案

来自文档:

例如，在Perl中，'Z'+1变为'AA'，而在C中，'Z'+1变为'['(ord('Z') == 90，ord('[') == 91).

For example, in Perl 'Z'+1 turns into 'AA', while in C 'Z'+1 turns into '[' ( ord('Z') == 90, ord('[') == 91 ).

请注意，字符变量可以递增但不能递减，即使如此，仅支持纯ASCII字符(a-z和A-Z).

Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

来自评论:-
还应注意，<=是词典比较，因此'z'+1 ≤ 'z'. (自'z'+1 = 'aa' ≤ 'z'起.但是'za' ≤ 'z'是第一次比较不正确.)例如，在$i == 'z'可行时中断.

From Comments:-
It should also be noted that <= is a lexicographical comparison, so 'z'+1 ≤ 'z'. (Since 'z'+1 = 'aa' ≤ 'z'. But 'za' ≤ 'z' is the first time the comparison is false.) Breaking when $i == 'z' would work, for instance.

此处的示例.

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