PHP 备忘单涵盖基本语法和函数

<?php // single-line comment

/*
  multi-line comment
*/

// variables
$variable_name = "value";  // string
$number = 123;             // integer
$float = 12.34;            // float
$boolean = true;           // boolean
$array = [1, 2, 3];        // array

// constants
define("constant_name", "value");
const another_constant = "value";
?>

<?php $str = "hello";
$str2 = 'world';
$combined = $str . " " . $str2; // concatenation

// string functions
strlen($str);            // length of a string
strpos($str, "e");       // position of first occurrence
str_replace("e", "a", $str); // replace all occurrences
?>

<?php $array = [1, 2, 3];
$assoc_array = ["key1" => "value1", "key2" => "value2"];

// array functions
count($array);                  // count elements
array_push($array, 4);          // add an element
array_merge($array, [4, 5]);    // merge arrays
in_array(2, $array);            // check if element exists
?>

<?php if ($condition) {
    // code to execute if true
} elseif ($another_condition) {
    // code to execute if another condition is true
} else {
    // code to execute if all conditions are false
}
?>

<?php switch ($variable) {
    case "value1":
        // code to execute if variable equals value1
        break;
    case "value2":
        // code to execute if variable equals value2
        break;
    default:
        // code to execute if no case matches
}
?>

<?php // for loop
for ($i = 0; $i < 10; $i++) {
    // code to execute
}

// while loop
while ($condition) {
    // code to execute
}

// do-while loop
do {
    // code to execute
} while ($condition);

// foreach loop
foreach ($array as $value) {
    // code to execute
}
?>

<?php function functionname($param1, $param2) {
    // code to execute
    return $result;
}

$result = functionname($arg1, $arg2);
?>

<?php // reading a file
$file = fopen("filename.txt", "r");
$content = fread($file, filesize("filename.txt"));
fclose($file);

// writing to a file
$file = fopen("filename.txt", "w");
fwrite($file, "hello, world!");
fclose($file);
?>

<?php try {
    // code that may throw an exception
    if ($condition) {
        throw new exception("error message");
    }
} catch (exception $e) {
    // code to handle the exception
    echo "caught exception: " . $e->getmessage();
} finally {
    // code to always execute
}
?>

<?php // create connection
$conn = new mysqli($servername, $username, $password, $dbname);

// check connection
if ($conn->connect_error) {
    die("connection failed: " . $conn->connect_error);
}

// select data
$sql = "select id, firstname, lastname from myguests";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "id: " . $row["id"]. " - name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
    }
} else {
    echo "0 results";
}

$conn->close();
?>

<?php // start session
session_start();

// set session variables
$_session["username"] = "johndoe";
$_session["email"] = "john@example.com";

// get session variables
echo $_session["username"];

// destroy session
session_destroy();
?>

<?php include 'filename.php';  // Includes file, gives a warning if not found
require 'filename.php';  // Includes file, gives a fatal error if not found

include_once 'filename.php';  // Includes file once, checks if already included
require_once 'filename.php';  // Requires file once, checks if already included
?>