php - PHP 宇宙飞船运算符 <=> 如何精确地处理字符串？

Question

我对字符串上宇宙飞船运算符的功能有点困惑。 在documentation他们说比较是根据PHP的常用类型comparison rules进行的但我还不清楚! 我看了这个stackoverflow question并做了一些测试，但仍然感到困惑。

这是我测试的代码:

<?php

$str1 = "aaa";
$str2 = "aaaa";

echo $str1 <=> $str2, PHP_EOL; // -1

$str1 = "baaaaaa";
$str2 = "abbb";

echo $str1 <=> $str2, PHP_EOL; // 1

$str1 = "aaaaaaa";
$str2 = "bbbb";

echo $str1 <=> $str2, PHP_EOL; // -1

它如何使用 ASCII 值？感谢您的帮助。

Answer 1

比较两个表达式。

For string it uses the ASCII values.

当第一个表达式分别小于、等于或大于第二个表达式时，返回-1、0或1。

// Integers
echo 1 <=> 1; // 0
echo 1 <=> 2; // -1
echo 2 <=> 1; // 1
 
// Floats
echo 1.5 <=> 1.5; // 0
echo 1.5 <=> 2.5; // -1
echo 2.5 <=> 1.5; // 1
 
// Strings
echo "a" <=> "a"; // 0
echo "a" <=> "b"; // -1
echo "b" <=> "a"; // 1
 
echo "a" <=> "aa"; // -1
echo "zz" <=> "aa"; // 1
 
// Arrays
echo [] <=> []; // 0
echo [1, 2, 3] <=> [1, 2, 3]; // 0
echo [1, 2, 3] <=> []; // 1
echo [1, 2, 3] <=> [1, 2, 1]; // 1
echo [1, 2, 3] <=> [1, 2, 4]; // -1
 
// Objects
$a = (object) ["a" => "b"]; 
$b = (object) ["a" => "b"]; 
echo $a <=> $b; // 0
 
$a = (object) ["a" => "b"]; 
$b = (object) ["a" => "c"]; 
echo $a <=> $b; // -1
 
$a = (object) ["a" => "c"]; 
$b = (object) ["a" => "b"]; 
echo $a <=> $b; // 1
 
// not only values are compared; keys must match
$a = (object) ["a" => "b"]; 
$b = (object) ["b" => "b"]; 
echo $a <=> $b; // 1