PHP恒里面IF

Question

有问题在PHP想，如果有人可以解释常数：

这个作品

const _ROOT = 'd:/aphp/www'; 

echo "r="._ROOT; 

为做到这一点：

if (true) 
     define('_ROOT','d:/aphp/www'); 

echo "r="._ROOT; 

但是这给了错误：解析错误：语法错误，意外T_CONST

if (true) 
    const _ROOT = 'd:/aphp/www'; 

echo "r="._ROOT; 

我使用PHP 5.3.2

Answer 1

那是因为...

的const关键字必须在顶层范围

从PHP文件

Note: As opposed to defining constants using define(), constants defined using the const keyword must be declared at the top-level scope because they are defined at compile-time. This means that they cannot be declared inside functions, loops or if statements.

Source声明