PHP Type Conversion Constant System Constant Magic Constant Detailed Explanation

PHP Type Conversion, Constant, System Constant, Magic Constant Detailed Explanation

1. Automatic type conversion;

 Automatic type conversion is performed during operation and judgment ;
1 ) Other types of conversion bool, Transition when judging ;
  1 ) Integer to Boolean: 0 Turn false, Non 0 Convert to true ; 
  2)  Empty string and ' 0' (" 0 ") Convert to false Other conversions true;
  3)  Empty array converted to false,  Non-empty arrays are converted to true;
  4) null Convert to false
  5)  Unsuccessful resource opening for false 
     Yes 0 Or empty, open unsuccessful turn to ' false','0';
2) Convert other types to strings ( String splicing );
  null bool int float
  1) null Convert to empty string ( Empty strings are not displayed )
  2) Integer directly converted to corresponding string  5=>'5';
  3) The real number is directly converted to the corresponding string, but the tail 0 Do not turn ( Last decimal point of real number 0);
  4)true Convert to '1 ', false Convert to empty string ;
 String, Boolean, Integer, Floating Point, null
3)  Type conversion that occurs during operation 
  1)true/false Conversion 1/0;
  2)null Convert to 0 ; 
  3) The value of the part at the beginning of the string is replaced by the corresponding value ;
  4) If there is no numeric value at the beginning of the string, it 0 ; 
   ( null,string,bool) < int < float

2. Force type conversion

 Is to handle it manually 1 To another 1 Values of types ;
  1 Type conversion function  intval ,strval, floatval
    $num1 = 1.2;
    $num2 = strval($num1); // Right $num1 To a string ;
    var_dump($num1); 
    var_dump($num2); 
  2 , ( Type )$ Variable    Can't be converted resource
    $num2 = (unset)$num2; Turn to null 
  3 , settype( Variable , Type )  Type must be written as a string ;
     Change the type and value of a variable ;
   Matters needing attention 
    1 ) Turn floating-point numbers into integers and directly kill decimals; 
    2) echo(int)($num1 + 0.5); 4 Shed 5 Into 

3. Constants

1) Constant definition 
  define( Constant name, constant value )
  define( ' SONG',22);
 Attention :
  1) The constant name is a string; 
  2) Constant value must be scalar 
  3) Constant name 1 Like capitalization, it is different from variables; 
  4) Constant names and variable names have the same naming rules ;
2) System constant 
  __LINE__  Current line number 
  __FILE__  The name of the current file 
  __DIR__  The directory of the current file; 
  PHP_OS   Operating system 
  PHP_VERSION php Version of 

 Magic constant :
__FUNCTION__  Function name 
__FUNCTION__ Function name ;
__CLASS__  Class name 
__CLASS__  Class name 
__METHOD__ Method name 
__METHOD__ Method citizen 
__NAMESPACE__  Name space 
__NAMESPACE__  Name space ;
3 ) Constant judgment 
  defined( Constant name )  Constant name must be a string; 
   Determine whether a constant has been defined ;

4. Operators and expressions;

1 ) Arithmetic operator  + - ( Multiplication ) /( Division ) % .
% Finding modulus / Remaining 
0 % 3 = 0
12 % 10 = 2
5 % 19 = 4
1 % 3 = 1 ; 
2 % 3 = 2 ; 
3 % 3 = 0 ; 
-9 % 4 = -1
9 % -4 = 1 ; 
 The sign of the result of modular operation depends on the first 1 Number. 
 Judge parity 
X%2 == 0  Is even and divisible 
X%2 != 0  Is odd and cannot be divisible 
2 * 3 = 8
 Exponential operation ;
2 3 = 8 ; 
3 2 = 9;

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