基于empty函数的判断详解

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$a = '''';
echo ''1.-----------''.($a == '''').''<br>'';
echo ''2.-----------''.($a == null).''<br>'';
echo ''3.-----------''.($a == false).''<br>'';
echo ''4.-----------''.($a == ''0'').''<br>'';
echo ''5.-----------''.($a == 0).''<br>'';
$a = null;
echo ''6.-----------''.($a == '''').''<br>'';
echo ''7.-----------''.($a == null).''<br>'';
echo ''8.-----------''.($a == false).''<br>'';
echo ''9.-----------''.($a == ''0'').''<br>'';
echo ''10.-----------''.($a == 0).''<br>'';
$a = ''0'';
echo ''11.-----------''.($a == '''').''<br>'';
echo ''12.-----------''.($a == null).''<br>'';
echo ''13.-----------''.($a == false).''<br>'';
echo ''14.-----------''.($a == ''0'').''<br>'';
echo ''15.-----------''.($a == 0).''<br>'';
$a = 0;
echo ''16.-----------''.($a == '''').''<br>'';
echo ''17.-----------''.($a == null).''<br>'';
echo ''18.-----------''.($a == false).''<br>'';
echo ''19.-----------''.($a == ''0'').''<br>'';
echo ''20.-----------''.($a == 0).''<br>'';
$a = false;
echo ''21.-----------''.($a == '''').''<br>'';
echo ''22.-----------''.($a == null).''<br>'';
echo ''23.-----------''.($a == false).''<br>'';
echo ''24.-----------''.($a == ''0'').''<br>'';
echo ''25.-----------''.($a == 0).''<br>'';
输出的结果
1.-----------1
2.-----------1
3.-----------1
4.-----------
5.-----------1
6.-----------1
7.-----------1
8.-----------1
9.-----------
10.-----------1
11.-----------
12.-----------
13.-----------1
14.-----------1
15.-----------1
16.-----------1
17.-----------1
18.-----------1
19.-----------1
20.-----------1
21.-----------1
22.-----------1
23.-----------1
24.-----------1
25.-----------1

$a = '''';//0|''0''|false|null 输出的结果一致
echo ''1.-------''.(!empty($a) == '''').''<br>'';
echo ''2.-------''.(!empty($a) == null).''<br>'';
echo ''3.-------''.(!empty($a) == false).''<br>'';
echo ''4.-------''.(!empty($a) == ''0'').''<br>'';
echo ''5.-------''.(!empty($a) == 0).''<br>'';

输出的结果：
1.-------1
2.-------1
3.-------1
4.-------1
5.-------1