如何比较不存在的数组字段?

How can you compare non-existing array fields?

没有$ num ['b']字段，有这些字段，其数组[4] (index 0..3)

there is no $num['b'] field, there are these fields, its array[4] (index 0..3)

• a:1
• a:2
• a:3
• b:2

$num在第一次迭代中将保持不变

$num in first iteration will hold

array("a"=>1);

因此，如果您想与"b":2进行比较，则必须使用以下模式:

so if you wanna compare to "b":2 you have to use this pattern:

$cmpr = array_shift($json);
...
if($num != $cmpr)

Array_shift: http://php.net/manual/zh/function. array-shift.php

Array_shift : http://php.net/manual/en/function.array-shift.php