Detailed analysis of constants and variables in PHP

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Examples of constants and variables in PHP

"PHP receives parameters under command line"

If you debug PHP at the command line, the incoming parameters are obtained through $ARGV, note that the file name contains the element, and the number of elements in the array is obtained by $ARGC.

"Mutable variables"

Refers to the variable name variable, the identifier of the variable can be replaced by the value of another variable.

For example, the second statement assigns a value to the ARGV1 variable.

<?php    $varName = ' argv1 ';   $ $varName = ' value1 ';   Var_dump ($argv 1);  ? >

constant

Use define definition, not delete and modify, write name directly when calling. Define also has a three-parameter version, and the third parameter indicates whether it is case insensitive and defaults to false.

<?php    define (' pi ', 3.14);   echo pi;  ? >

Tip: First check that constants are defined and redefined, using the defined function:

<?php    if (!defined (' pi '))     define (' pi ', 3.14);   else     Echo ' pi has been defined<br> ';  ? >

For constants with special symbols, you need to use the constant function to call, note that this constant name should be quoted, for example:

<?php    if (!defined (' = = '))     define (' = = ', ' puzzled ');   else     Echo ' pi has been defined<br> ';      ECHO constant (' = = ');  >

Gets all the constants that have been defined:

<?php      Var_dump (get_defined_constants ());  ? >

"Magic Variable"

__line__ gets the current row, __file__ gets the current path.

An application:

Use the Str_replace function to replace file names in files with paths + filenames to ensure that file path changes are still accessible.

Str_replace (< value to find >,< replace with value >,< searched string >,< Replacement count variable (optional) >);

<?php      define (' ROOT ', str_replace (' a.php ', ' ', __file__ ');      echo ROOT;  ? >

"In-System"

Before the number 0 is octal, plus 0x is hexadecimal.

"String Type"

Double and single quotes are possible, but double quotes resolve internal variables, but single quotes are efficient.

Double quotation-Mark parsing variable: {} can be guaranteed to separate variable names from other parts.

<?php    $name = "Test";   echo "username is {$name}";  ? >

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