Definitions of constants and variables in PHP, usage, and examples of differences

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, and 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}";  ? >