Php constant _ PHP Tutorial

Php constants. Naming rules for constants: the same naming rules as variables: define () function format: define (constant name, value); example: define (PI, 3.14 ); constants and variables are the same: 1: naming rules for naming constants

Naming: The same naming rules as variables

Method: define () function

Format: define ('constant name', 'Specific Value ');

Example: define ('pi ', 3.14 );

Comparison between constants and variables

Same:

1: The naming rules are the same (but generally in uppercase)

Different:

1: $ is not used when a constant is referenced, and the name is used directly.

2: constants can only be defined using define, but cannot be defined using a value assignment statement.

3: once defined, constants cannot be redefined or undefined.

4: the constant value can only be a scalar (only integer, floating point, Boolean, numeric, or NULL)

[Php]

// Define a constant

Define ('pi ', 3.14 );

// Area of the computing Park

$ R = 3;

Echo pi * $ r;

// Result: 28.26

// After a constant is defined, it cannot be redefined.

Define ('pi ', 3.23 );

// Result: Notice: Constant pi already defined in C: \ wamp \ www \ 0124 \ 05.php on line 15

// The constant cannot be assigned a value again.

Pi = 100;

Echo pi;

// Result: Parse error: syntax error, unexpected '= 'in C: \ wamp \ www \ 0124 \ 05.php on line 21

// Syntax errors

$ PI = 10;

Function text (){

Echo $ PI; // The function has a scope. This $ PI variable is not the same as $ PI in the function.

Echo pi; // A constant defined once, which can be used anywhere

}

// Result: Notice: Undefined variable: PI in C: \ wamp \ www \ 0124 \ 05.php on line 31

Text ();

?>

How can I determine whether a constant is defined?

Define defines constants

Defined judge constant

[Php]

If (defined ('pi ')){

Echo 'pi constant has been defined.
';

} Else {

Echo 'pi constant is undefined. let me define it.
';

Define ('pi ', 33322 );

}

Echo PI;

?>

[Php]

Result: The PI constant is undefined. I will define it.

33322

Naming rule: the same naming rule method as the variable: define () function format: define (constant name, specific value); example: define (PI, 3.14 ); constants and variables are the same: 1: name...