PHP general knowledge review: custom functions and internal functions

1. Variable scope and static variables

Function parameters and parameter reference transfer

Function return Value and reference returns

Import of external files

Inspection of system built-in functions

Variables The scope of a variable is also called the scope of a variable. The scope of a variable is the context in which it is defined (also the scope in which it takes effect). Most PHP variables have only one valid scope, and this single scope also includes files introduced by include and require.

global keyword

$GLOBALS and other super-global arrays

Static variables are only in Exists in the local function scope, and its value will not disappear when the program execution leaves the scope.

static keyword

1. Only initialize once

2. Assignment is required during initialization

3. The value will be retained every time the function is executed

4. The modified function is local and is only saved inside the function

　 5. The number of function calls can be recorded to terminate the recursion under certain conditions

function myFunc(){
static $a = 1;
echo $a++;
}
myFunc()；        //1
myFunc()；        //2
myFunc()；        //3

<?php
$count = 5;
function getCount(){
static $count;
return $count++;
}
echo $count;        //5
$count++;


echo getCount();    //null
echo getCount();    //1 null + 1 = 1
?>

Functions are passed by value by default, if you want the function to modify its value, you must pass it by reference.

<?php
$a = 1;
function myFun(&$a){
$a = 100;
}
myFun($a);
echo $a;        //100
?>

2. The return value of the function

The value is returned through the optional return statement

Any type including an array or object can be returned

The return statement will terminate the execution of the function and return control to the control point of the function

If return is omitted, the return value is null

It is impossible to have multiple return values

To return a reference from a function, you must use the reference operator when declaring the function and assigning the return value to a variable. Import of external files

include/reqlude Difference warning/fatal error include_once/reqlude_once

3. System built-in functions

Time and date: date(), strtottime(), time(), miketime(), microtime(), date_default_timezone_set()

IP processing function: iptolong(), longtoip()

Print processing: print(), printf(), print_r(), echo, sprintf(), var_dump() , var_export()

Serialization and deserialization functions: serialize(), unserialize() https://www.cnblogs.com/yamtsin/p/5922872.html

String Processing function: implod()

Problem-solving method:

Focus on memorizing the relevant content of the PHP function definition, understand the variable scope, static variables, function parameters, and return values, focus on memorizing the relevant content Built-in function for summarization.

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