PHP: Learning Notes

Posted 2020-10-15 三叁

php basics

in PHP, variables are defined as $_alphanum 

variables should always prefixed a $

variables defined/assigned outside of a function cannot be used inside a function, unless declared inside function with keyword global $var. Also can be used as $GLOBALS[‘var‘] for in/out.

echo variables: (all of the 3 examples are okay)

echo $x
echo "x is equal to $x"
echo "x is equal to " . $x

comments can be:

# comments
// comments
/* comments */

the static keyword inside function keeps the variable change everytime calls the function.

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php functions

echo: what echo echoes is pure-html, can be tagged htmls. echo strings concat using .,  echo variables can do math ops. echo multiple elements separated by ,

print: print only accept one element, returns 1, slower

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php types

• String
• Integer
• Float (floating point numbers - also called double)
• Boolean
• Array
• Object
• NULL
• Resource

var_dump($var) function dumps a var together with its type

bool: false true

create arrays by array() constructor. $x= array("a","b","c")

object are instances of class, class can be defined by:

class Car {
    function Car() {
        $this->model = "VW";
    }
}

instantialize it to object by new:

$herbie = new Car();

any var created without init is as null.

resource type: relating to db calls

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php string manipulating

strlen(): counts to last ‘\0‘

str_word_count(): counts words

strrev(), reverse a string str->rts

strpos(str, pattern), returns start of pattern idx in str

str_replace(patt, rep, str) returns str‘s all pattern replaced by rep

complete list of string funcs: here

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php constants

define(name,value[,opt-case-sensitive])

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php arith

===, ==, !=, !==, ++, --, and(&&), or(||), xor, !,

.=: str concat

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php cond

if, switch($var)->case:->break->default:

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php function

<?php
function func($val=40) //func with opt parm val, defaults to 40
{}

func(); //call it
?>

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php array

count($arr) returns count of array elems

array can also be created in associative way:

$age = array("Peter"=>"35", "Ben"=>"37", "Joe"=>"43");

foreach($age as $x => $x_value) {
    echo "Key=" . $x . ", Value=" . $x_value;
    echo "<br>";
}

array can be called recursively to create multi-level array

complete array intro is here.

sorting an array in different ways: sort, rsort, asort, ksort, arsort, krsort.. indexed/associative arrays are sorted using different functions

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php globals

• $GLOBALS
• $_SERVER
• $_REQUEST
• $_POST
• $_GET
• $_FILES
• $_ENV
• $_COOKIE
• $_SESSION

$GLOBALS is introd before

$_SERVER[‘HTTP_USER_AGENT‘] returns user-agent field of the incoming request. other fields can be PHP_SELF, SERVER_NAME, HTTP_HOST, SCRIPT_NAME, REQUEST_METHOD.. more to look at here.

$_REQUEST[‘varname‘] is used to collect the value of the input field from a form.

$_POST[‘varname‘] is used to collect the value of a post http request with key=varname

$_GET[‘varname‘] is used to collect the value of a request which has uri: domain.com/page.html?varname=value 

post key-values may be embedded in ssl/tls, so its sneaker than get option