PHP constant crash

1 Simple Assignment

1  <?php  // Preliminary simple to assign a constant value of 2  define('PI ', 3.14); 3  Echo PI

2 Parametric analysis

Define (name, Value,bool)

First parameter

　　 Name constant names are generally named in uppercase.

A second parameter

value To assign a value to a parameter, it must be a scalar (integer, float, Boolean, String type).

First parameter

　　If the bool constant name is case-insensitive , the default is False when the value is not assigned. 　

<?  define(' NUM ', 3.14,trueecho NUM;  // The result of the output is 3.14 Define (' num ', 3.14,falseecho NUM;  // The result of the output is num Define (' NUM ', 3.14echo NUM;  // The result of the output is num//where the  second third is the same situation.

3 Some characteristics of constants

• A constant can only be assigned a value once.
• by definded (), you can detect whether a variable has been assigned a value.

<? PHP      Define (' NUM ', 3.14);     Var_dump (defined// output is bool (true)

4 The difference between a variable and a constant

1. Variables can be assigned directly and constants can only be define () to assign values
2. The name of a constant cannot be used in $, while a variable can.
3. Constants are not scoped anywhere defined as global constants, and variables have scopes.
4. Once a constant is defined, the variable can be modified.
5. The value of a constant can only be scalar.

5 new features for PHP 5.3

<? PHP Define (' NUM ', 3.14); Echo   NUM; Define ('-_-# ', 3.14); // echo  -_-#;  Obviously cannot output echoconstant//php5.3 constant can handle this special case

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PHP constant crash