Introductory tutorial on php variables, basic knowledge of php variables

$a = 'hello';
function test() {
var_dump($a);
}
// test();
include 'b.inc';

b.inc content:

echo 'hello';
?>

The program can output hello normally, but the commented out test() cannot be parsed normally because of the variable $a is undefined.

4. Use global variables If you want to use global variables in a function, you can use the following two methods.

global keyword global $a, $b; When a global variable is declared in a function, all references to any variable point to its global version.

$GLOBALS super global variable array $GLOBALS['b'] = $GLOBALS['a'] + $BLOBALS['b']; Usage is similar to the global keyword.

5. Static variables Static variables only exist in the local function scope, but their values ​​are not lost when program execution leaves this scope. Moreover, it is only initialized once when it is declared, and the value of the static function will not be overwritten each time the function is called.

Assigning a static variable with the result of an expression in the declaration will cause a parsing error. Static declarations are parsed at compile time.

function test() {
static $cnt = 0;
echo $cnt;
$cnt++;
if($cnt < 10) {
test();
}
 $cnt--;
}
test();

is similar to static in C language. The following C code can also output ten numbers from 0 to 9 in sequence.

#include
void test(void) {
static int cnt = 0;
printf("%d ", cnt);
cnt++;
if(cnt < 10) {
test();
}
cnt--;
}
int main(void) {
test();
return 0;
}

The static and global definitions of variables are Implemented by reference.

5. Variable variables Variable variables are a special usage in PHP language. I don’t know if they exist in other languages.

In short, a variable variable means that a variable variable obtains the value of an ordinary variable as the variable name of the variable variable.

$a = 'hello';
$$a = 'world';
echo "$a $$a"; // hello $hello
echo "$a ${$ a}"; // hello world

When mutable variables are used in arrays, ambiguity may arise. For example, if you write $$a[1], the compiler will report an error. The meaning you want to express needs to be replaced in the following two ways.

${$a[1]} $a[1] as a variable

${$a}[1] $$a acts as a variable and takes out the value with index 1 in the variable.

6. Form variables When a form is submitted to a PHP script, the information in the form is automatically available in the script and can be accessed via $_GET[], $_POST[] and $_REQUEST[].

Note that dots and spaces in variable names are converted to underscores. For example, becomes $_REQUEST["a_b"]. The following example shows the use of identifiers in the form.

form Process file process.php.

var_dump(isset($_POST['my.text']));
var_dump(isset($_POST['mytext']));
var_dump(isset($_POST[ 'my_text']));
var_dump($_POST['my_text']);

Because the period is not a legal character in PHP variable names, the output result is: boolean false boolean false boolean true

string 'h3' (length=2) The magic_quotes_gpc configuration directive affects the value of get/post/cooie. This feature has been deprecated and removed. Single quotes, double quotes, backslashes and NULL characters in the input will not be escaped. If you need to escape, you can use addslashes(). If you need to dequote a quoted string, you need to use stripslashes().

php also understands arrays in form variable context.

Example, use more complex form variables and post the form to yourself and display the data on submission.

if(isset($_POST['action'])) {
var_dump($_POST);
} else {
$page = $_SERVER['PHP_SELF'];
$ s = <<



ab
c



STR;
echo $s;
}

Be extra careful when containing complex variables in the heredoc. The above code $_SERVER['PHP_SELF'] without curly brackets will cause an error when running.

if(isset($_POST['action'])) {
var_dump($_POST);
} else {
$s = <<< form action="{$_SERVER['PHP_SELF']}" method="post">



STR;
echo $s;
}

For the above program, when the user clicks on the picture At some point, the form will be sent to the server, and two variables sub_x and sub_y will be added, containing the coordinates of the user's clicked image.

array (size=3) 'action' => string '1' (length=1) 'sub_x' => string '334' (length=3) 'sub_y' => string '282' (length=3) cookies

php can set cookies with the setcookie() function. Cookies are part of the http information header, so they must be called before sending any output to the browser.

php cookies use:

Cookie data is available in the corresponding cookie array. If multiple values ​​are assigned to a cookie variable, they must be assigned to an array.