php determine data type

isset ():                         // Whether the variable has been declared 
empty ():                         // Whether the variable is empty 
defined ():　　　　　　　　　　　　　　　　　　　　　　　// Whether the constant has been defined define() 
array_key_exists ( mixed  key , array search):         // Check the given key name or if the index exists in the array

is_numeric ( mixed  var ):                 // Check whether the variable is a number or a number string 
is_bool ():             // Check whether the variable is a boolean 
is_float ():             // Check whether the variable is a floating point type and is_double, is_real() are the same Usage 
is_int ():             // Check if the variable is an integer is_integer() Same usage 
is_string ():             // Check if the variable is a string 
is_object ():             // Check if the variable is an object 
is_array ():             // Check if the variable is an object Whether the variable is an array 
is_null ():             // Check whether the variable is NULL whether the value is NULL case-sensitive