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sagaxu 只要是连续的索引型数组,那 json_encode 后肯定就是 []
php > $a = [2 => 'a', 6 => 'b'];
php > var_export(json_encode($a));
'{"2":"a","6":"b"}'
php > $a = [2 => 'a', 0 => 'c', 1 => 'd'];
php > var_export(json_encode($a));
'{"2":"a","0":"c","1":"d"}'
php > sort($a);
php > var_export(json_encode($a));
'["a","c","d"]'
php > $a = ['2' => 'a', '0' => 'c', '1' => 'd'];
php > var_export(json_encode($a));
'{"2":"a","0":"c","1":"d"}'
php > sort($a);
php > var_export(json_encode($a));
'["a","c","d"]'