close contact with PHP variables, constant learning notes (read notes from PHP manual)
A dollar sign ($) in PHP follows a variable name, representing a variable. The name of the variable is case sensitive. where the variable name
allow numbers or underscores to begin。
to assign a value to a variable's pass address
In PHP 3, variables are always assigned values. PHP 4 provides another way to assign a value to a variable: to send an address assignment. Use
Send address Assignment, that is, simply
append A (&) symbol to the variable that will be assigned the value(source variable). This means that the new variable simply references the original variable,
changing the new variable will affect the original variableVice versa.
<?php
$foo = ' Bob ';
$bar = & $foo;
$bar = "My name is $bar";
Echo $bar;
Echo $foo;
?>
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Variable foo is only assigned in the first row and normally output as "Bob", however, the value of variable foo changes as the variable bar value changes, but the assignment is assigned to the variable bar.
about (Super) global variables
The declaration of a PHP global variable is declared when the variable is referenced, not as a global or a local variable when the first line of the program is defined or assigned.
<?php
$a = 1;
$b = 2;
function Sum ()
{
Global $a, $b;
$b = $a + $b;
}
Sum ();
Echo $b;
?>
|
If the global variable is not declared using global in the function sum (), the program complains about the undefined variable.
Of course, there are variables in PHP that do not require global declarations within the scope of a program's functionality, which are called
Super global variable, and these hyper-global variables are basically not user-defined, but PHP predefined variables, such as $_get, $_post, $_cookie, and so on.
about variable variables
The more interesting variable variables in PHP, such as $a = "Bruce", can also be expressed as $bruce by using $ $a, variable is the two dollar sign used.
But in $ $a [1], is $a [1] as a variable, or $ $a as a variable and take out the value indexed by [1] in that variable?
There 's no back-and-forth relationship here., but instead uses the ${$a [1]} or ${$a}[1] to represent both of these situations.
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about Constants
Constants are distinguished from variables, and their scope is global by definition of constants.
Volume defaults to case sensitivity, which is always capitalized according to the Convention constant identifier
Constants not preceded by dollar sign ($)
Constants cannot be redefined or undefined once they are defined
Constants can only be defined with the Define () function, not by assignment statements
For example, define ("MyName", "cnbruce") is defined as a MyName constant with a value of "Cnbruce"
<?php
Define ("MyName", "cnbruce");
$MYNAME = "Cnrose";
Echo myname;
Echo $MYNAME;
? |
