What is the static variable mechanism of PHP functions?

The static variable mechanism of PHP functions allows variables to retain their values ​​between function calls, thereby achieving the following functionality: Preserving state between function calls. Avoid creating duplicate variables. Simplify the code.

Static variable mechanism of PHP function

Introduction

Static variable is a A special variable scope that exists only inside a function and retains its value each time the function is called. This is different from regular variables, which are reset after each function call.

Syntax

To declare a static variable, just precede the variable with the static keyword, as shown below:

function foo() {
  static $counter = 0;
  $counter++;
  echo $counter;
}

Practical Case

Suppose we want to create a function that prints an incrementing counter every time it is called. Using static variables, we can easily achieve this:

function getCounter() {
  static $counter = 0;
  $counter++;
  return $counter;
}

echo getCounter();  // 输出 1
echo getCounter();  // 输出 2
echo getCounter();  // 输出 3

Difference from non-static variables

• Scope:Static variables only Exists inside a function, whereas non-static variables are created when the function is called.
• Visibility: Static variables are visible inside the function, while non-static variables are not visible outside the function.
• Assignment: Static variables can be assigned values, but non-static variables can only be assigned once.

Advantages

• Preserves state between function calls.
• Avoid creating duplicate variables.
• Simplify the code.

Note

• Because static variables retain their value between function calls, they need to be used with caution to avoid unexpected side effects.
• When a function is included in other functions, the scope of static variables will be expanded.

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