2018/03/07 daily One learn PHP constants Defind and const differences

What is a constant?

A literal understanding of the amount of non-change during the execution of a script.

What should be noted for defining a constant?

1: The constants are case sensitive, and the case of the error is not recognized as a constant.

2: Constants can only be scalar data, but also define resource constants, but defined, there will be some wonderful, unpredictable errors, so should be avoided as far as possible.

Scalar data: (Boolean,integer,float and string)

by Defind and const differences

1: Duplicate definition

1:defind repeating constants, constants will not be modified, PHP report a notification error;

Error:

　　　　　　　　　　

Conclusion:

Although it does not affect the operation of the program, the problem should be reduced alone.

　　　　　　1:const repeatedly defines constants, fatal errors.

Error:

　　　　　　　　　　

2:Defind can not be used in the class, otherwise the fatal error is reported

Error:

　　　　　　　　　　

　　　　3:const can only be defined within a class and cannot be defined in a method, conditional statement

　　　　4: Pick:

　　　　　　Using const makes the code easy to read, and const itself is a language structure, and define is a function. In addition, the const is much faster to compile than define.

5: Correlation function

defined-checks if a constant exists for a name

constant-returns the value of a constant

Get_defined_constants -Returns an associative array of all constants

After the study, if in the encounter other, in addition.

2018/03/07 Daily Learn PHP constants Defind and const differences