# PHP代码优化

## 优化1：if的使用技巧之“给定初始值”

```php
if (1 == $orderState) {
   $orderTitle = '已预定';
} else {
   $orderTitle = '已售完';
}

// 优化后
$orderTitle = '已售完';
if (1 == $orderState) {
 $orderTitle = '已预定';
}
```

## 优化2：if的使用技巧之“用"&&" 替换 if

```php
if (strlen($newPwd) < 6) {
    $message = '密码长度不足!';
}

strlen($newPwd) < 6 && $message = '密码长度不足!';
```

## 优化3：if的使用技巧之“三元运算符替换”

```php
if (empty($_POST['action'])) {
    $action = 'default';
} else {
    $action = $_POST['action'];
}

//优化后
$action = empty($_POST['action']) ? 'default' : $_POST['action'];
```

## 优化4：简化“三元运算符”

```php
$action = empty($_POST['action']) ? 'default' : $_POST['action'];
// 简写后
echo $action = $_POST['action'] ?:'default' ;
//必须保证action必须是存在的，否则Notice: Undefined index: a xxx
```

## 优化5：if的使用技巧之“去掉多此一举的if”

```php
function isLeapYear($year) {
    if (($year % 4 == 0 && 100 !=0) || ($year % 400 == 0)) {
        return true;
    } else {
        return false;
    }
}
//优化后
function isLeapYear($year) {
    return ($year % 4 == 0 && 100 !=0) || ($year % 400 == 0);
}
```

比如写js的时候

```javascript
 $('#selStatus').bind('change',function(){
     $(this).val() == 'disabled' ? $('.reason').removeClass('hidden') : $('.reason').addClass('hidden');
 });
```

## 优化6：“ else if ”能如何被改进呢？

```php
if ('玄幻' == $sortname) {
    $sort = 1;
} else if ('武侠' == $sortname) {
    $sort = 2;
} else if ('言情' == $sortname) {
    $sort = 3;
} else if ('其他' == $sortname) {
    $sort = 10;
}
//优化后
switch ($sortname) {
    case '玄幻':
        $sort = 1;
        break;
    case '武侠':
        $sort = 2;
        break;
    case '言情':
        $sort = 3;
        break;
    case '其他':
        $sort = 10;
        break;
}
```

## 优化7：：表驱动法替代“else if”

```php
$sortTable = array(
    '玄幻' => 1,
    '武侠' => 2,
    '言情' => 3,
    '其他' => 10,
);
$sortId = $sortTable[$sortname];
```

## 优化8：循环语句几个要点

* 用while(true) 表示无限循环，别用for
* 特定情况下\[发邮件、采集网页]，要加延时sleep
* 循环体内尽可能不用函数或更耗资源的调用
* foreach代替while和for循环（PHP）
* 避免空循环
* 只做一件事,尽可能短，控制在50行以内
* 循环嵌套限制在3层以内

## 优化9：使用更精悍短小的代码

* 函数的最佳**最大长度**是50-150行代码
* 函数参数**不超过7个**
* 短小函数更容易理解也方便修改
* 只做一件事情的函数更易于复用
* 短小的函数测试更方便

## 优化10：避免使用幻数（magic numbers）

```php
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8" />

//优化后
define('APP_CHARSET', 'UTF-8');
<meta http-equiv="Content-Type" content="text/html;charset={APP_CHARSET}" />
```

[幻数浅析（Magic Number）](http://blog.csdn.net/yinshitaoyuan/article/details/51233157)

将一些比较难理解的东西，定义的常量（类中），这样代码可读性高

## 优化11：中间结果赋值给变量

```php
$str = 'this_is_a_test';
$humpstr = implode('', array_map('ucfirst', explode('_', $str)));

// 优化后
$str = $str = 'this_is_a_test';
$words   = explode('_', $str);
$uWords  = array_map('ucfirst', $words);
$humpstr = implode('', $uWords);
```

## 优化12：复杂的逻辑表达式做成布尔函数

```php
if (!$hasone && $ddisfirst = 1 && $litpic == '' && empty($litpicname)) {
    $litpcname = GetImageMapDD($iurl, $cfg_ddimg_width);;
}

// 优化后
$emptyPic = ($litpic == '' && empty($litpicname));
$validFirstPic = (!$hasone && $ddisfirst);
if ($validFirstPic && $emptyPic) {
    $litpcname = GetImageMapDD($iurl, $cfg_ddimg_width);;
}
```

## 优化13：永远不要复制粘贴雷同的代码

* 相同的代码放一起让以后修改更轻松
* 可以让全局的统计和过滤器等实现方便
* 可复用的带参函数是解决雷同代码的好办法


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