Differences after adding static keywords to variables and functions in PHP _php tutorial

Static global variable and normal global variable, static local variable and ordinary local variable, static function and ordinary function difference? The following article will answer for you.
　　
(1) The description of the global variable (external variable) is then prefixed with static, which constitutes a global variable. Global variables themselves are static storage, and static global variables are, of course, static storage methods. The two are not different in how they are stored. The difference between the two is that the scope of the non-static global variable is the entire source program, when a source program consists of multiple source files, non-static global variables are valid in each source file. A static global variable restricts its scope, which is valid only within the source file that defines the variable, and cannot be used in other source files of the same source program. Because the scope of a static global variable is limited to one source file, it can be common only for functions within that source file, so you avoid causing errors in other source files.

(2) from the above analysis, it can be seen that changing the local variable to a static variable changes its storage mode, which changes its life time. Changing a global variable to a static variable changes its scope and limits its scope of use.

(3) The static function differs from the normal function scope only in this file. Functions that are used only in the current source file should be described as intrinsic (static) and intrinsic functions should be described and defined in the current source file. For functions that can be used outside of the current source file, it should be stated in a header file that the source file to use these functions should contain the header file.

Sum up:

What is the difference between a static global variable and a normal global variable?

The static global variable is only initialized once, preventing it from being referenced in other file units;
　
What is the difference between a static local variable and a normal local variable?

The static local variable is initialized only once, the next time based on the last result value;
　
What is the difference between a static function and a normal function?

The static function has only one copy in memory, and the normal function maintains one copy in each invocation;

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