这个PHP语法是什么意思？

Question

Consider the code:

$a = "foobar";
echo $a{3}; // prints b

I know $a[3] is 'b' but how come using {} in place of [] produec the same result ?

Answer 1

You can read here in official documentation about braces:

String s may also be accessed using braces, as in $str{42}, for the same purpose. However, this syntax is deprecated as of PHP 5.3.0. Use square brackets instead, such as $str[42].

Answer 2

EDIT This thread may interest you: "dropping curly braces"

It's just an alternative syntax; the two forms compile to exactly the same bytecode:

<?php
$str = "aaab";
echo $str{3}; 
echo $str[3]; 

number of ops:  9
compiled vars:  !0 = $str
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
   2     0  >   EXT_STMT                                                 
         1      ASSIGN                                                   !0, 'aaab'
   3     2      EXT_STMT                                                 
         3      FETCH_DIM_R                                      $1      !0, 3
         4      ECHO                                                     $1
   4     5      EXT_STMT                                                 
         6      FETCH_DIM_R                                      $2      !0, 3
         7      ECHO                                                     $2
         8    > RETURN                                                   1

Answer 3

它是相同的，但从PHP 5.3开始不推荐使用{}语法。

Answer 4

{} and [] are the same. it is your choice what to use. [] is more common though.