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Detailed graphic explanation of constants and variables in php

May 21, 2018 am 10:27 AM
php Graphics and text Detailed explanation

This article mainly introduces relevant information about the detailed explanation of constants and variable instances in php. Friends who need it can refer to

Detailed explanation of constants and variable instances in php

[PHP receives parameters on the command line]

If debugging php on the command line, the incoming parameters are obtained through $argv. Note that it contains the file name element. , the number of elements in the array is obtained through $argc.

【Variable variable】

means that the name of the variable is variable, and the identifier of the variable can be determined by the value of another variable. replace.

For example: the second statement assigns a value to the variable argv1.

<?php 
 
  $varName = &#39;argv1&#39;; 
  $$varName = &#39;value1&#39;; 
  var_dump($argv1); 
 
?>
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【Constant】

Use define to define, cannot be deleted or modified, call When writing the name directly. define also has a three-parameter version. The third parameter represents whether it is case-insensitive. The default is false.

<?php 
 
  define(&#39;pi&#39;,3.14); 
  echo pi; 
 
?>
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Tips: Check whether the constant is defined before defining it, use the defined function:

<?php 
 
  if(!defined(&#39;pi&#39;)) 
    define(&#39;pi&#39;,3.14); 
  else 
    echo &#39;pi has been defined<br>&#39;; 
 
?>
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For constants with special symbols, you need to use the constant function to call them. Note that the constant name should be enclosed in quotes, for example:

<?php 
 
  if(!defined(&#39;= =&#39;)) 
    define(&#39;= =&#39;,&#39;puzzled&#39;); 
  else 
    echo &#39;pi has been defined<br>&#39;; 
   
  echo constant(&#39;= =&#39;); 
 
?>
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Get all defined constants:

<?php 
   
  var_dump(get_defined_constants()); 
 
?>
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[Magic Variable]

__LINE__ gets the current line, __FILE__ gets the current path.

An application:

Use the str_replace function to replace the file name in the file with the file name to ensure that the file path changes can still be accessed.

str_replace(,,, );

<?php 
   
  define(&#39;ROOT&#39;,str_replace(&#39;a.php&#39;,&#39;&#39;,__FILE__)); 
   
  echo ROOT; 
 
?>
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【Base】

Add 0 before the number is octal , plus 0x is hexadecimal.

[String type]

Both double quotes and single quotes can be used, but double quotes can parse internal variables, but single quotes are more efficient .

Double quotes parse variables: { } can ensure that the variable name is separated from other parts.

<?php 
 
  $name = "test"; 
  echo "username is {$name}"; 
 
?>
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PHP variablesDetailed explanation and string dynamic insertion of variables ( Case)

PHP variablesDetailed explanation of scope

Detailed explanation of PHP constants and data type instances

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