PHP array key values use single and double quotes and unsigned differences

PHP array key values use single and double quotes and unsigned differences

Method/Step

2. 1

   The first: $array [' key '] This single quote key value pattern can be parsed directly into an array that is $array

   The second type: $array ["key"] this double-quote key-value pattern, the first execution is "key", to determine whether there is a defined PHP variable exists, parsing the array is $array

   Third: $array [key] This is a no single double quote key value mode, which first parses the presence of a constant that has a key key value definition, that is, using define (' key ', ' Val '), and then parsing the array as $array

4. 2

   Other conditions: For example $array["$a"] and $array[$a] differences

   1. $array ["$a"], $array [$a] in this case, the value of the array is parsed by the array subscript of the string type

   2. $array ["$a"], $array [$a] This situation has no meaning if the index type is an array

   3. $array ["$a"], $array [$a] This situation can not care about single double quotes, stating that $ A is a variable, that is $array["$a"]=== $array [$a]

6. 3

   Detailed Examples:

   <?php

   Define (' Chang ', ' array1 ');

   $chang = ' $array 2 ';

   $bian = ' array1 ';

   $array = Array (

   ' Array1 ' = ' array1 ',

   ' $array 2 ' = ' $array 2 ',

   ' $array 3 ' = ' $array 3 ',

   );

   echo $array [' array1 ']. ' <br/> ';

   echo $array ["$bian"], ' <br/> ';

   Echo $array [Chang], ' <br/> ';

   echo $array [$chang];

PHP array key values use single and double quotes and unsigned differences