php提示Notice: Undefined index 错误解决办法

if($a)
{
 echo $a;
}
else
{

}

//解决

$a=1;
if($a)
{
 echo $a;
}
else
{

}

//输出1
//在文章头部加

error_reporting(0);

if($a)
{
 echo $a;
}
else
{

}

<?php
echo(strtotime("now"));
echo(strtotime("3 October 2005"));
echo(strtotime("+5 hours"));
echo(strtotime("+1 week"));
echo(strtotime("+1 week 3 days 7 hours 5 seconds"));
echo(strtotime("next Monday"));
echo(strtotime("last Sunday"));
?>

输出：

1138614504
1128290400
1138632504
1139219304
1139503709
1139180400
1138489200

$a = date();
$mk = strtotime($a)

<?
$y=date("Y",time());
$m=date("m",time());
$d=date("d",time());
$start_time = mktime(9, 0, 0, $m, $d ,$y);
$end_time = mktime(19, 0, 0, $m, $d ,$y);

$time = time();
if($time >= $start_time && $time <= $end_time)
{
// do something....
}
?>

<?
$time = time();
$date = date("Y-m-d",$time);
echo 'www.111cn.net 提示'.$date
?>

<?php

// this是指向当前对象的指针

class test_this{
    private $content; //定义变量
   
    function __construct($content){ //定义构造函数
          $this->content= $content;
    }
    function __destruct(){}//定义析构函数
   
    function printContent(){//定义打印函数
        echo $this->content.'<br />';
    }
}

$test=new test_this('北京欢迎你！'); //实例化对象
$test->printContent();//北京欢迎你！

//parent是指向父类的指针

class test_parent{ //基类
    public $name;  //定义姓名  父类成员需要定义为public，才能够在继承类中直接使用 this来调用。
    function __construct($name){
        $this->name=$name;
    }
}
class test_son extends test_parent{ //派生类  继承test_parent
    public $gender;//定义性别
    public $age;    //定义年龄
    function __construct($gender,$age){ //继承类的构造函数
        parent::__construct('nostop');//使用parent调用父类的构造函数,来进行对父类的实例化
        $this->gender=$gender;
        $this->age=$age;
    }
    function __destruct(){}
    function print_info(){
        echo $this->name.'是个'.$this->gender.'，今年'.$this->age.'岁'.'<br />';
    }
}

$nostop=new test_son('女性','22');//实例化test_son对象
$nostop->print_info();//执行输出函数  nostop是个女性，今年23岁

class clss_a {
    
     private static  $name="static class_a";
    
     const PI=3.14;
     public $value;   
        
     public static function getName()
     {
        return self::$name;   
     }
     //这种写法有误，静态方法不能访问非静态属性
     public static function getName2()
     {
         return self::$value;
     }
     public function getPI()
     {
       return self::PI;   
     }
    
    
 }

class person{
function _ _destruct( )
{ echo "bye bye !“; }
}
$a=new person();

class Address{
     protected $city;
     protected $country;

     public function setCity($city){$this->city = $city;}
     public function getCity(){return $this->city;}
     public function setCountry($country){$this->country = $country;}
     public function getCountry(){return $this->country;}
}

class Person{
     protected $name;
     protected $address;
     //浅克隆
     public function __construct(){
          $this->address = new Address;
     }

     public function setName($name){
          $this->name = $name;
     }
     public function getName(){
          return $this->name;
     }

     public function __call($method,$arguments){
          if(method_exists($this->address,$method)){
               return call_user_func_array(array($this->address,$method),$arguments);
          }
     }
     //深克隆
     public function __clone(){
          $this->address = clone $this->address;
     }
}

$test1 = new Person;
$test2 = clone $test1;

$test1->setName('testname1');
$test1->setCity('testcity1');
$test2->setName('testname2');
$test2->setCity('testcity2');

echo $test1->getName().'-'.$test1->getCity()."n";
echo $test2->getName().'-'.$test2->getCity()."n";
//testname1-testcity2
//testname2-testcity2

class Person{
     protected $__data = array('email','test');

     public function __get($property){
          if(isset($this->__data[$property])){
               return $this->__data[$property];
          }else{
               return false;
          }
     }

     public function __set($property,$value){
          if(isset($this->__data[$property])){
               return $this->__data[$property] = $value;
          }else{
               return false;
          }
     }
 
     public function __isset($property){
          if(isset($this->__data[$property])){
               return true;
          }else{
               return false;
          }
     }
 
     public function __unset($property){
          if(isset($this->__data[$property])){
               return unset($this->__data[$property]);
          }else{
               return false;
          }
     }
}

$test = new Person;
$test->email= 'test';
var_dump($test->email);

if (empty($C_char)) return false; //是否已设定

if ($C_char=='') return false; //是否为空

<?php
$str = '';

if($str==='') {//''==null ''==false ''!==false
echo 'str is a NULL string.';
}
?>

<?php
$var = 0;
// 结果为 true，因为 $var 为空
if (empty($var)) {
    echo '$var is either 0 or not set at all';
}
// 结果为 false，因为 $var 已设置
if (!isset($var)) {
    echo '$var is not set at all';
}
?>

function demo(){
  $var = _post['a'];//接受过来的参数 
echo   " isset测试:<Br> " ;
if  ( isset ( $var ))n  
{ 
echo   ' 变量$var存在!<Br> '  ;
}else
{
echo   ' 变量$var不存在!<Br> '  ;
}
echo   " empty测试:<Br> " ;
if  ( empty ( $var )){    
echo   ' 变量$var的值为空<Br> ' ;
} 
else
{
  
echo   ' 变量$var的值不为空<Br> ' ;
}
echo   " 变量直接测试:<Br> " ;
if  ( $var ){
     
echo   ' 变量$var存在!<Br> ' ; 
}  
else {
echo   ' 变量$var不存在!<Br> ' ;
}