深入理解PHP：高级技巧、面向对象与核心技术（原书第3版） -- 高级 PHP 技巧

echo "<pre>";
$students = array(
    256 => array("name" => "Jon", "grade" => 98.5),
    2 => array("name" => "Vance", "grade" => 85.1),
    9 => array("name" => "Stephen", "grade" => 94.0),
    364 => array("name" => "Steve", "grade" => 85.1),
    68 => array("name" => "Rob", "grade" => 74.6)
);

// Name sorting function:
function name_sort($x, $y) {
    return strcasecmp($x["name"], $y["name"]);
}

// Sort by name:
uasort($students, "name_sort");
echo print_r($students, 1);        // 1 保存结果，而不是打印结果

---

echo "<pre>";
$students = array(
    256 => array("name" => "Jon", "grade" => 98.5),
    2 => array("name" => "Vance", "grade" => 85.1),
    9 => array("name" => "Stephen", "grade" => 94.0),
    364 => array("name" => "Steve", "grade" => 85.1),
    68 => array("name" => "Rob", "grade" => 74.6)
);

function name_sort($x, $y) {
    // Show iterations using a static variable:
    static $count = 1;
    echo "<p>Iteration $count: {$x["name"]} vs. {$y["name"]}</p>
";
    $count++;
    return strcasecmp($x["name"], $y["name"]);
}

// Sort by name:
uasort($students, "name_sort");
echo "<h2>Array Sorted By Name</h2><pre>" . print_r($students, 1) . "</pre>";

---

echo "<pre>";
$students = array(
    256 => array("name" => "Jon", "grade" => 98.5),
    2 => array("name" => "Vance", "grade" => 85.1),
    9 => array("name" => "Stephen", "grade" => 94.0),
    364 => array("name" => "Steve", "grade" => 85.1),
    68 => array("name" => "Rob", "grade" => 74.6)
);

uasort($students, function($x, $y) {
    return strcasecmp($x["name"], $y["name"]);
});

// Sort by name:
uasort($students, "name_sort");
echo "<h2>Array Sorted By Name</h2><pre>" . print_r($students, 1) . "</pre>";

if (isset($_GET["id"]) && filter_var($_GET["id"], FILTER_VALIDATE_INT, ["options"=>["min_range"=>1]]) ) {
    $id = $_GET["id"];
} else {
    $id = 0;
}
echo $id;

$q = sprintf("INSERT INTO tasks (parent_id, task) VALUES (%d, "%s")", $parent_id, mysqli_real_escape_string($dbc, strip_tags($_POST["task"]))); 

# 格式如下:%["padding_character"][-][width][.precision]type
     所有的转换说明都是以%开始,如果想打印一个%符号,必须用%%.
     参数"padding_character"是可选.它将被用来填充变量直至所指定的宽度.该参数的作用就在变量前面填充.默认的填充字符是一个空格,如果指定0或者空格,就不需要 " 单引号作为前缀,其他字符就必须指定 " 作为前缀.
     参数 - 是可选.它指左对齐,默认是右对齐.
     参数width是指被替换的变量的长度.
     参数precision表示以小数点开始.它指明小数点后要显示的位数.
     参数type 是类型码,请看下表:
类型     |   含义
b       |    解释为整数并作为二进制输出.
c       |    解释为整数并作为字符表示输出(ASCII码).
d       |   解释为整数并作为整数输出.
f       |   解释为双精度并作为浮点数输出.
o       |   解释为整数并作为八进制数输出.
s       |   解释为字符串并为字符串输出.
u       |   解释为整数并作为非指定小数输出.
x       |    解释为整数并作为带有小写字母a-f的十六进制数输出
X       |   解释为整数并作为带有大写字母A-F的十六进制数输出

printf("%0.2f",12);     // 12.00
printf("%0.2f",12.2);   // 12.20
printf("%0.2f",12.23);  // 12.23