PHP variable and date processing cases

This article mainly introduces PHP variables and date processing cases. Interested friends can refer to it. I hope it will be helpful to everyone.

Variable related
Internal implementation of PHP variablesThe system types of programming languages ​​are divided into two types: strong type and weak type:

1. Strong Type language means that once a variable is declared as a variable of a certain type, a value other than the type of the variable cannot be assigned to it during the running of the program. Languages ​​such as c/c/java fall into this category

2. Scripting languages ​​such as php, ruby, and javascript are weakly typed languages: a variable can represent any data type

php Variable types and storage structuresWhen php declares or uses variables, it does not need to explicitly indicate its data type

php is a weakly typed language. This does not mean that php has no type. In php, There are 8 types of variables, which can be divided into three categories:

1. Scalar type: boolean, integer, float, string

2. Composite type: array ,object

3. ## Special type: resource,NULL

Variable storage structureThe value of the variable is stored in In the zval structure shown. Its structure is as follows:

  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 
  };

The value of the variable is stored in another structure zvalue_value

Variable typezval structure The type field is the most critical field to implement weak types. The value of type can be one of: IS_NULL, IS_BOOL, IS_LONG, IS_DOUBLE, IS_STRING, IS_ARRAY, IS_OBJECT, IS_RESOURCE. It is easy to understand literally, they are only the only types of Mark, store different values ​​in the value field according to different types

Storage of variable valuesAs mentioned earlier, the value of the variable is stored in the zvalue_value structure, and the structure is defined as follows:

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

Date related

 <?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";

Summary:That’s it The entire content of this article is hoped to be helpful to everyone's study.

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