php 判断常量、变量和函数是否存在

if (defined('CONST_NAME')) {
    //do something 
}

if (isset($var_name)) {
    //do something
}

函数检测用function_exists，注意待检测的函数名也需要使用引号，如：

if (function_exists('fun_name')) {
 fun_name();
}

<?php
/* 判断常量是否存在*/
if (defined('MYCONSTANT')) {
echo MYCONSTANT;
}
//判断变量是否存在
if (isset($myvar)) {
echo "存在变量$myvar.";
}
//判断函数是否存在
if (function_exists('imap_open')) {
echo "存在函数imag_openn";
} else {
echo "函数imag_open不存在n";
}
?>

<?php
/**
 * Tanphp framework
 *
 *
 * @category   Tanphp
 * @package    Data_structure
 * @copyright  Copyright (c) 2012 谭博  tanbo.name
 * @version    $Id: Tree.php 25024 2012-11-26 22:22:22 tanbo $
 */

/**
 * 树形结构数据存取类
 *
 * 用于对树形结构数据进行快速的存取
 *
 * @param array $arr 参数必须为标准的二维数组，包含索引字段（id）与表示树形结构的字段(path),如example中所示
 *
 * @example <code>
 * $arr = array(
 *  array( 'id' => 1, 'name' => 'php', 'path' => '1' ),
 *  array( 'id' => 3, 'name' => 'php1', 'path' => '1-3' ),
 *  array( 'id' => 2, 'name' => 'mysql', 'path' => '2' ),
 *  array( 'id' => 6, 'name' => 'mysql1', 'path' => '2-6' ),
 *  array( 'id' => 7, 'name' => 'mysql2', 'path' => '2-7' ),
 *  array( 'id' => 5, 'name' => 'php11', 'path' => '1-3-5' ),
 *  array( 'id' => 4, 'name' => 'php2', 'path' => '1-4' ),
 *   );
 *  $cate = new Tree($arr);
 * 
 *  $data = $cate->getChild(2);
 * 
 *  print_r($data->toArray());
 * </code>
 *
 */

class Tree
{
    public  $_info;                             //节点信息
    public  $_child = array();                  //子节点
    private $_parent;                           //父节点
    private $_data;                             //当前操作的临时数据
    private static $_indexs         = array();  //所有节点的索引
    private static $_index_key      = 'id';     //索引键
    private static $_tree_key       = 'path';   //树形结构表达键
    private static $_tree_delimiter = '-';      //属性结构表达分割符
   
   
   
    /**
     * 构造函数
     *
     * @param array $arr
     * @param boole $force_sort 如果为真，将会强制对$arr 进行排序
     * @return void
     */
    public function __construct(array $arr = array(),  $force_sort=true)
    {
        if ($force_sort === true) {
            $arr=$this->_array_sort($arr, self::$_tree_key);
        }
        if (!empty($arr)) {
            $this->_init($arr);
        }
    }
   
    /**
     * 初始存储树形数据
     *
     * @param array $arr
     * @return void
     */
    private function _init(array $arr)
    {
        foreach ($arr as $item) {
            $path        = $item[self::$_tree_key];
            $paths       = explode(self::$_tree_delimiter, $path);
            $count_paths = count($paths);
            $parent_id   = isset($paths[$count_paths-2]) ? $paths[$count_paths-2] : NULL;
           
            if (   $count_paths>1                                   //如果有父级
                && array_key_exists($parent_id, self::$_indexs)      //父级已经被存入索引
                && self::$_indexs[$parent_id] instanceof Tree    //父级为Tree对象
            ) {
                self::$_indexs[$parent_id]->addChild($item);
            } elseif ($count_paths == 1) {
                $this->addChild($item);
            } else {
                throw new Exception("path数据错误".var_export($item, true));
            }
           
        }
       
        //print_r(self::$_indexs);
    }
   
    /**
     * 添加子节点
     *
     * @param array $item
     * @return void
     */
    public function addChild(array $item, $parent = NULL)
    {
        $child          = new Tree();
        $child->_info   = $item;
        $child->_parent = $parent == NULL ? $this : $parent;
        $child->_parent->_child[] =  $child;
       
        $this->_addIndex($item, $child->_getSelf());
    }
   
    /**
     * 添加节点到索引
     *
     * @param array $item
     * @param mix $value
     * @return void
     */
    private function _addIndex(array $item, $value)
    {
        if (array_key_exists(self::$_index_key, $item) && is_int($item[self::$_index_key])) {
            self::$_indexs[$item[self::$_index_key]] = $value;
        } else {
            throw new Exception("id字段不存在或者不为字符串");
        }
    }
   
   
    /**
     * 获取对自己的引用
     *
     * @return Tree object quote
     */
    private function _getSelf()
    {
        return $this;
    }
   
    /**
     * 获取指定id的节点的子节点
     *
     * @param int $id
     * @return Tree object
     */
    public function getChild($id)
    {
        $data       = self::$_indexs[$id]->_child;
        $this->_data = $data;
        return $this;
    }
   
    /**
     * 获取指定id的节点的父节点
     *
     * @param int $id
     * @return Tree object
     */
    public function getParent($id)
    {
        $data = self::$_indexs[$id]->_parent;
        $this->_data = $data;
        return $this;
    }
   
    /**
     * 获取指定id的节点的同级节点
     *
     * @param int $id
     * @return Tree object
     */
    public function getBrother($id)
    {
        $data = self::$_indexs[$id]->_parent->_child;
        $this->_data = $data;
        return $this;
    }
   
    /**
     * 将Tree对象转化为数组
     *
     * @param  object $object
     * @return array
     */
     public function toArray($obj = NULL)
     {
        $obj  = ($obj === NULL) ? $this->_data : $obj;
        $arr  = array();
        $_arr = is_object($obj) ? $this->_getBaseInfo($obj) : $obj;
       
        if (is_array($_arr)) {
            foreach ($_arr as $key => $val){
               
                $val = (is_array($val) || is_object($val)) ? $this->toArray($val) : $val;
                   
                $arr[$key] = $val;
            }
        } else {
            throw new Exception("_arr不是数组");
        }
       
    
        return $arr;
    }
   
    /**
     * 过滤_parent等字段，以免造成无限循环
     *
     * @param object $obj
     * @return void
     */
    private function _getBaseInfo($obj)
    {
        $vars = get_object_vars($obj);
        $baseInfo['_info']  =  $vars['_info'];
        $baseInfo['_child'] =  $vars['_child'];
        return $baseInfo;
    }
   
    /**
     * 二维数组排序
     *
     * 根据指定的键名对二维数组进行升序或者降序排列
     *
     * @param array  $arr 二维数组
     * @param string $keys
     * @param string $type 必须为 asc或desc
     * @throws 当参数非法时抛出异常
     * @return 返回排序好的数组
     */
    private function _array_sort(array $arr, $keys, $type = 'asc') {
        if (!is_string($keys)) {
            throw new Exception("非法参数keys:参数keys的类型必须为字符串");
        }
   
        $keysvalue = $new_array = array();
        foreach ($arr as $k=>$v) {
            if (!is_array($v) || !isset($v[$keys])) {
                throw new Exception("参数arr不是二维数组或arr子元素中不存在键'{$keys}'");
            }
            $keysvalue[$k] = $v[$keys];
        }
   
        switch ($type) {
            case 'asc':
                asort($keysvalue);
                break;
            case 'desc':
                arsort($keysvalue);
                break;
            default:
                throw new Exception("非法参数type ：参数type的值必须为 'asc' 或 'desc'");
        }
   
        reset($keysvalue);
        foreach ($keysvalue as $k=>$v) {
            $new_array[$k] = $arr[$k];
        }
        return $new_array;
    }
   
}

?>

function daysbetweendates($date1, $date2){
    $date1 = strtotime($date1);
    $date2 = strtotime($date2);
    $days = ceil(abs($date1 - $date2)/86400);
    return $days;
}

<?php
functionmaketime($date)
{
list($year,$month,$day) = explode('-',$date);
returnmktime(0,0,0,$month,$day,$year);
}
$date1 = '2007-01-08';
$date2 = '2007-03-01';
$d = (maketime($date2) - maketime($date1)) / (3600*24);
echo'相差$d 天';

?>

<?php
/**
 *  计算.生肖
 * 
 * @param int $year 年份
 * @return str
 */
function get_animal($year){
    $animals = array(
            '鼠', '牛', '虎', '兔', '龙', '蛇', 
            '马', '羊', '猴', '鸡', '狗', '猪'
    );
    $key = ($year - 1900) % 12;
    return $animals[$key];
}

echo get_animal(1990);    // 马
echo get_animal(2010);    // 虎

<?php
/**
 *  计算.星座
 *
 * @param int $month 月份
 * @param int $day 日期
 * @return str
 */
function get_constellation($month, $day){
    $signs = array(
            array('20'=>'宝瓶座'), array('19'=>'双鱼座'),
            array('21'=>'白羊座'), array('20'=>'金牛座'),
            array('21'=>'双子座'), array('22'=>'巨蟹座'),
            array('23'=>'狮子座'), array('23'=>'处女座'),
            array('23'=>'天秤座'), array('24'=>'天蝎座'),
            array('22'=>'射手座'), array('22'=>'摩羯座')
    );
    $key = (int)$month - 1;
    list($startSign, $signName) = each($signs[$key]);
    if( $day < $startSign ){
        $key = $month - 2 < 0 ? $month = 11 : $month -= 2;
        list($startSign, $signName) = each($signs[$key]);
    }
    return $signName;
}

echo get_constellation(12, 11);    // 射手座
echo get_constellation(6, 6);      // 双子座

$header = get_headers($url, 1);
if (strpos($header[0], ’301′) || strpos($header[0], ’302′)) {
if (is_array($header['Location'])) {
return $header['Location'][count($header['Location'])-1];
} else {
return $header['Location'];
}
} else {
return $url;
}

<?php
//
echo get_redirect_url('http://www.111cN.nEt');
//输出结果为：http://code.google.com/android/
function get_redirect_url($url){
    $redirect_url = null;

    $url_parts = @parse_url($url);
    if (!$url_parts) return false;
    if (!isset($url_parts['host'])) return false; //can't process relative URLs
    if (!isset($url_parts['path'])) $url_parts['path'] = '/';

    $sock = fsockopen($url_parts['host'], (isset($url_parts['port']) ? (int)$url_parts['port'] : 80), $errno, $errstr, 30);
    if (!$sock) return false;

    $request = "HEAD " . $url_parts['path'] . (isset($url_parts['query']) ? '?'.$url_parts['query'] : '') . " HTTP/1.1rn";
    $request .= 'Host: ' . $url_parts['host'] . "rn";
    $request .= "Connection: Closernrn";
    fwrite($sock, $request);
    $response = '';
    while(!feof($sock)) $response .= fread($sock, 8192);
    fclose($sock);

    if (preg_match('/^Location: (.+?)$/m', $response, $matches)){
        if ( substr($matches[1], 0, 1) == "/" )
            return $url_parts['scheme'] . "://" . $url_parts['host'] . trim($matches[1]);
        else
            return trim($matches[1]);

    } else {
        return false;
    }

}