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HomeBackend DevelopmentPHP TutorialPHP的关于变量和日期处理的一些面试题目整理_php实例

变量相关
PHP变量的内部实现
编程语言的系统类型分为强类型和弱类型两种:

  1.     强类型语言是一旦某个变量被申明为某个类型的变量,在程序运行过程中,就不能将该变量的类型以外的值赋予给它,c/c++/java等语言就属于这类
  2.     php及ruby,javascript等脚本语言就属于弱类型语言:一个变量可以表示任意的数据类型


php变量类型及存储结构
php在声明或使用变量的时候,并不需要显式指明其数据类型

php是弱类型语言,这不并表示php没有类型,在php中,存在8种变量类型,可以分为三类:

  1.     标量类型:boolean,integer,float,string
  2.     复合类型:array,object
  3.     特殊类型:resource,NULL


变量存储结构
变量的值存储到一下所示的zval结构体中.其结构如下:

  typedef struct _zval_struct zval; 
   
  struct _zval_struct { 
    zvalue_value value; // 存储变量的值 
    zend_uint refcount__gc; // 表示引用计数 
    zend_uchar type;  // 变量具体的类型 
    zend_uchar is_ref_gc;  // 表示是否为引用 
  }; 


变量的值存储在另外一个结构体zvalue_value中

变量类型
zval结构体的type字段就是实现弱类型最关键的字段了,type的值可以为:IS_NULL, IS_BOOL, IS_LONG, IS_DOUBLE, IS_STRING, IS_ARRAY, IS_OBJECT, IS_RESOURCE之一.从字面上就很好理解,他们只是类型的唯一标示,根据类型的不同将不同的值存储到value字段

变量值的存储
前面说到变量的值存储在zvalue_value结构体中,结构体定义如下:

  typedef union _zvalue_value { 
    long lval; 
    double dval; 
    struct { 
      char *val; 
      int len; 
    } str; 
    HashTable *ht; 
    zend_object_value obj; 
  } _zvalue_value; 


日期相关

计算两个日期之间的天数
  

 <&#63;php 
   
  /** 
   * 求两个日期之间相差的天数(针对1970年1月1日之后,求之前可以采用泰勒公式) 
   * @param string $day1 
   * @param string $day2 
   * @return number 
   */ 
  function diffBetweenTwoDays ($day1, $day2) 
  { 
    $second1 = strtotime($day1); 
    $second2 = strtotime($day2); 
     
    if ($second1 < $second2) { 
      $tmp = $second2; 
      $second2 = $second1; 
      $second1 = $tmp; 
    } 
     
    return ($second1 - $second2) / 86400; 
  } 
   
  $day1 = "2013-07-27"; 
  $day2 = "2013-08-04"; 
   
  $diff = diffBetweenTwoDays($day1, $day2); 
  echo $diff."\n"; 

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