Surely you have a closet or chest of drawers at home. The principle of their use is simple: we put things there that we do not need right now, but may be needed after a while.
Variables are arranged in exactly the same way. You can put some value in them and store it there until you need it.
You can put a value in a variable like this:
In the code above, we created the $name variable and put the value Ivan into it, then we created the $age variable and assigned the value 20 to it.
The name "variable" means that its value can change during script execution:
In some languages, a variable must first be "declared" before being used. There is no declaration in PHP - a variable is created the moment you put a value into it.
However, PHP programmers often say "declare a variable" instead of "create a variable".
Also instead of "put in variable value" is often said to "assign a value".
The reason is simple - the symbol = , thanks to which we store the value in a variable, is called the "assignment operator". Hence the term "assign".
1. The variable name begins with the $ symbol.
2. The second character can be a letter or an underscore _
Variable names are case sensitive. $name and $Name are different variables.
You can display a variable using the echo command already known to us:
The echo command allows you to display multiple values at once:
Note that we passed 2 values to echo, separating them with a comma. So we can pass as many values as we want. The following two examples will produce the same result:
Also in PHP there is a shorthand syntax for outputting variables. Instead of
Prior to PHP 5.4, the shorthand syntax only worked when included in PHP settings the short_open_tag directive, which also allows you to use a shortened opening tag
The echo command is not always convenient for checking the current value of a variable. For example, if you try to display an empty string "" absolutely nothing will be displayed on the screen. And it is not clear what the reason is - in an empty variable or non-working code.
Therefore, the var_dump() function is used to check the value of a variable:
Result of script execution:
String(5) "Vasya" string(0) ""
As you can see, PHP outputs not only the contents of the variable, but also the number of characters, and even the type of the variable (string). We will look at data types in detail in the next lessons.
You can remove an existing variable using the unset() function:
And now it's time to practice a little.
Remember, almost any PHP problem can have multiple solutions. Therefore, if your decisions differ from those written on this site, this does not mean at all that you have done something wrong.
Write a script that:
1. Creates variables named title and content and some values.
2. Displays the value of the title variable inside the h1 tag, and the value of the content variable inside the div tag.
Show Solution
", $title, ""; echo "
I want to once again draw your attention to the fact that this decision is not the only correct one. For example, the following code will produce the same result:
Environment variables (environment) in Windows contain various information about system settings and the user's environment. A distinction is made between user, system, and process environment variables.
The easiest way to view the contents of environment variables in Windows is to open the system properties ( sysdm.cpl) -> Advanced -> Environment Variables. As you can see, there are two sections in the opened section: the upper one contains the user's environment variables, the lower one contains the system ones.
In addition, environment variables are stored in the system registry. User variables are stored in the . Systemic - in HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment.
You can display the values of all environment variables in command line Windows. The command is simple:
The command will list the environment variables and their values.
In PowerShell, to display all environment variables, you can use the command:
If you want to display the value of only one variable, you need to use the echo command, and the variable name must be enclosed in percent signs. For example,
echo %systemroot%
set > c:\tmp\env_var.txt
The environment variables of a particular process can be obtained using the free Process Explorer utilities(from Sysinternals). Just open the process properties and go to the tab Environment.
variables in php is a kind of information container that can contain Various types data (text, numbers, arrays, and so on). In general, variables allow you to create, store, modify, and then quickly access the information specified in them.
How to name variables:
$var
$variable
$year1945
$_variable
How not to name variables:
$1 - consists of only a digit
$1var - you can't start a variable name with a number
$/var - only underscore is allowed from additional characters _
$variable - cyrillic is allowed by php documentation, but not recommended
$var iable - spaces cannot be used
Each variable is assigned a value. The sign is used to assign a value. =
(equals). During script processing, the value of a variable can change repeatedly depending on various conditions.
$city = "Moscow"; // the variable $city was assigned the string (in quotes) value Moscow
$year = 1147; // and the $year variable was assigned the numeric value 1147
?>
$name = "Alexander";
$Name = "Alex";
echo "$name, $Name"; // prints "Alexander, Alexey"
?>
// This is how we set the values of the variables
$name1 = "Alex";
$name2 = "Alexander";
// Display variables
echo $name2; // Output: Alexander
echo "name1 is $name1"; // name1 is Alexey
// Using single quotes output
// variable name, not value
echo "name1 is $name1"; // output: name1 is $name1
// you can display just the values of variables
echo $name1; // Alexei
echo $name1,$name2; // AlexeyAlexander
echo $name1." ".$name2; // Alexey Alexander
echo "$name1, $name2"; // Alexey, Alexander
echo<<
multiple lines with $variable substitution.
END;
-$a(negation) Change the sign of $a.
$a + $b(addition) The sum of $a and $b.
$a - $b(subtraction) The difference between $a and $b.
$a * $b(multiply) The product of $a and $b.
$a / $b(division) The quotient of $a divided by $b.
$a % $b(modulo) The integer remainder of $a divided by $b.
Consider examples
$a = 2; // note that in the case of numbers, quotes are not put
$b = 3; // note that in the case of numbers, quotes are not put
$result = $a + $b; // add variables
echo $result; // prints 5
$result = $b - $a; // add variables
echo $result; // prints 1
Increment and decrement operations in PHP
These operations will be useful mainly in the construction of cycles, which we will talk about a little later.
prefix- operators written BEFORE the variable ( --$a; ++$a). Return the value of the variable before changes.
Postfix- operators written after the variable ( $a--; $a--). Return the value of a variable with changes.
Increment- increasing the value.
Decrement- decreasing value.
++$a prefix increment. Increments $a by one and returns the value of $a.
$a++ postfix increment. Returns the value of $a and then increments $a by one.
--$a prefix decrement. Decrements $a by one and returns the value of $a.
$a-- Postfix decrement. Returns the value of $a and then decrements $a by one.
echo "
echo"
echo"
echo"
Assignment operations in PHP
Base operator looks like =
. At first glance, it might seem that this is the equals operator. Actually it is not. In effect, the assignment operator means that the left operand gets the value of the right expression, (i.e., is set to the resulting value). Combined Operators- these are operators that allow you to use the previous values of variables for subsequent operations (append to a string variable (with text) or add numeric values).
$a = ($b = 2) + 4; // result: $a is set to 6, $b is set to 2.
$a = 2;
$a += 3; // sets $a to 5, similar to $a = $a + 3;
$b = "Hi";
$b .= "Peace!"; // sets $b to "Hello World!" like $b = $b . "There!";
There are also comparison operations And brain teaser, but we will talk about them in the next lessons. I will try not to scare you with a large amount of information at once!)
13 years ago
A little gotcha to watch out for:
If you turn off RegisterGlobals and related, then use get_defined_vars(), you may see something like the following:
array
[ GLOBALS ] => Array
[ GLOBALS ] => Array
* RECURSION *
[_POST] => Array()
[_GET] => Array()
[_COOKIE] => Array()
[ _FILES ] => Array()
)
[_POST] => Array()
[_GET] => Array()
[_COOKIE] => Array()
[ _FILES ] => Array()
)
?>
Notice that $_SERVER isn"t there. It seems that php only loads the superglobal $_SERVER if it is used somewhere. You could do this:
print"
" .htmlspecialchars(print_r(get_defined_vars(), true )) . "" ;
" .htmlspecialchars (print_r ($_SERVER , true )) . "" ;
6 years ago
Since get_defined_vars() only gets the variables at the point you call the function, there is a simple way to get the variables defined within the current scope.
// The very top of your php script
$vars = get_defined_vars();
// Now do your stuff
$foo = "foo" ;
$bar = "bar" ;
// Get all the variables defined in current scope
$vars = array_diff(get_defined_vars(), $vars);
echo "
" ;" ;
print_r($vars);
echo "
15 years ago
Here is a function which generates a debug report for display or email
using get_defined_vars. Great for getting a detailed snapshot without
relying on user input.
function generateDebugReport ($method , $defined_vars , $email = "undefined" )(
// Function to create a debug report to display or email.
// Usage: generateDebugReport(method,get_defined_vars(),email);
// Where method is "browser" or "email".
// Create an ignore list for keys returned by "get_defined_vars".
// For example, HTTP_POST_VARS, HTTP_GET_VARS and others are
// redundant (same as _POST, _GET)
// Also include vars you want ignored for security reasons - i.e. PHPSESSID.
$ignorelist =array("HTTP_POST_VARS" , "HTTP_GET_VARS" ,
"HTTP_COOKIE_VARS" , "HTTP_SERVER_VARS" ,
"HTTP_ENV_VARS" , "HTTP_SESSION_VARS" ,
"_ENV" , "PHPSESSID" , "SESS_DBUSER" ,
"SESS_DBPASS" , "HTTP_COOKIE" );
$timestamp = date("m/d/y h:m:s" );
$message = "Debug report created $timestamp \n" ;
// Get the last SQL error for good measure, where $link is the resource identifier
// for mysql_connect. Comment out or modify for your database or abstraction setup.
global $link ;
$sql_error = mysql_error($link);
if($sql_error )(
$message .= "\nMysql Messages:\n" . mysql_error($link);
}
// End MySQL
// Could use a recursive function here. You get the idea ;-)
foreach($defined_vars as $key => $val )(
if(is_array ($val ) && ! in_array ($key , $ignorelist ) && count ($val ) > 0 )(
$message .= "\n $key array (key=value):\n" ;
foreach($val as $subkey => $subval )(
if(! in_array ($subkey , $ignorelist ) && ! is_array ($subval ))(
$message .= $subkey . "=" . $subval . "\n" ;
}
elseif(! in_array ($subkey , $ignorelist ) && is_array ($subval ))(
foreach($subval as $subsubkey => $subsubval )(
if(! in_array ($subsubkey , $ignorelist ))(
$message .= $subsubkey . "=" . $subsubval . "\n" ;
}
}
}
}
}
elseif(! is_array ($val ) && ! in_array ($key , $ignorelist ) && $val )(
$message .= "\nVariable " . $key. "=" . $val. "\n" ;
}
}
If($method == "browser" )(
echo nl2br($message);
}
elseif($method == "email" )(
if($email == "undefined" )(
$email = $_SERVER["SERVER_ADMIN"];
}
$mresult = mail ($email , "Debug Report for " . $_ENV [ "HOSTNAME" ]. "" , $message );
if($mresult == 1 )(
echo "Debug Report sent successfully.\n";
}
else(
echo "Failed to send Debug Report.\n";
}
}
}
?>
17 years ago
Simple routine to convert a get_defined_vars object to XML.
function obj2xml ($v , $indent = "" ) (
while (list($key , $val ) = each ($v )) (
if ($key == "__attr" ) continue;
// Check for __attr
if (is_object ($val -> __attr )) (
while (list($key2 , $val2 ) = each ($val -> __attr )) (
$attr .= " $key2 =\" $val2 \"" ;
}
}
else $attr = "" ;
if (is_array ($val ) || is_object ($val )) (
print(" $indent<
$key$attr
>\n");
obj2xml ($val , $indent . " " );
print(" $indent\n");
}
else print(" $indent<
$key$attr
>$val\n");
}
}
//Example object
$x -> name -> first = "John" ;
$x -> name -> last = "Smith" ;
$x -> arr [ "Fruit" ] = "Bannana" ;
$x -> arr [ "Veg" ] = "Carrot" ;
$y -> customer = $x ;
$y -> customer -> __attr -> id = "176C4" ;
$z = get_defined_vars();
obj2xml($z["y"]);
?>
will output:
11 years ago
As a note, get_defined_vars() does not return a set of variable references (as I hoped). For example:
// define a variable
$my_var = "foo" ;
// get our list of defined variables
$defined_vars = get_defined_vars();
// now try to change the value through the returned array
$defined_vars [ "my_var" ] = "bar" ;
echo $my_var , "\n" ;
?>
will output "foo" (the original value). It "d be nice if get_defined_vars() had an optional argument to make them references, but I imagine its a rather specialized request. You can do it yourself (less conveniently) with something like:
$defined_vars = array();
$var_names = array_keys(get_defined_vars());
foreach ($var_names as $var_name )
{
$defined_vars [ $var_name ] =& $ $var_name ;
}
?>
1 year ago
I posted here before about "this" being in get_defined_vars.
It turns out it "s not always there but in certain cases it will inexplicably appear.
Php -r"
class Test(
public function a() (var_dump(array_keys(get_defined_vars()));$a = 123;)
public function b() (var_dump(array_keys(get_defined_vars()));$this;)
}
$t = new Test();
$t->a();
$t->b();
"
array()
array("this")
This does not happen in PHP 7.2 but will happen in PHP 5.6.
1 year ago
Some comments here point out that this function wont return references. It does however return names and names are "references".
I would not recommend the suggestions here that convert it to references.
public function x($a, $b, $c) (
foreach(array_keys(get_defined_vars()) as $key)
if($key !== "this")
$this->y($($key));
}
Public function y(&$input) (
$input++;
}
Instead of $() you can also use $$.
I have done some whacky things in my time to make extremely generic code but I"ve never had to do anything like the above. It might not even work (but should since it"s no different to $a[$key]).
You could also do $$key++ but I"ve never seen code like that which wasn"t horrifically bad (using dynamic where dynamic isn"t beneficial).
If you"re doing something like that then give it additional scrutiny.
