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   • What is the differences between 'identifier' and 'reference' concepts in PHP programming language?

     Top Answer

     Answered Apr 16, 2020 · 2 votes

     Let us start with the last part of your quotation.

     And, when an object is sent by argument, returned or assigned to another variable, the different variables are not aliases: they hold a copy of the identifier, which points to the same object.

     Object Identifiers

     In general, an object identifier is an integer value that identifies an object. Let us create some objects from a bare class A. We would use SPL's spl_object_id() and var_dump() functions.

     Both functions return the object handle for the given object. The object handle is not a memory address.

     class A {}-$a = new A();$b = $a;-var_dump($a) . PHP_EOL;var_dump($b) . PHP_EOL;-// object(A)#1 (0) { Notice #1 - an identifier// }-// object(A)#1 (0) { Notice #1 - an identifier// }-echo spl_object_id($a) . PHP_EOL; // Outputs: 1 - an identifier echo spl_object_id($b) . PHP_EOL; // Outputs: 1 - an identifier-

     $a and $b hold a copy of the identifier, which points to the same object (A).

     If a PHP script created 500 objects, then each object id would be unique for the lifetime of the object. Each object id can be used as a key for storing objects, or for identifying an object, as long as the object is not destroyed/garbage collected. Once the object is destroyed, its id may be reused for other objects.

     Now, let us start with the first part of your quotation.

     References in PHP are a means to access the same variable content by different names and they are not actual memory addresses. Instead, they are symbol table aliases.

     Reference

     In PHP, reference has a different meaning. Therefore, it allows you to access a value with different variable names. A reference is created by the & operator in PHP:

     $a = 12;-// Notice the & (ampersand)$b = & $a; // $b = 12; -$b = 20; // $a = 20; now-

     Here we can access the value 20 using $a and $b. Ok! We now need to know what happens when we assign a value to a variable because you quoted that the different variable names are not actually memory address. Let us dig into that.

     zval Container

     A PHP variable is stored in a container called a zval. A zval container is created when a new variable is created with a constant value, such as:

     $a = "hello";-

     A zval container stores four types of information about a variable:

     • Type - variable's type
     • Value - variable's value
     • is_ref - a boolean value representing whether or not the variable is part of a "reference set"
     • refcount - holds how many variable names (also called symbols) point to this one zval container

     There is a function named xdebug_debug_zval() which is available when Xdebug is installed; It helps you dig into how a variable with a value resides in a zval container.

     $a = "hello";xdebug_debug_zval('a');-

     This outputs as the following:

     a: (refcount=1, is_ref=0)='hello'-

     Or graphically you can imagine the zval container as the following:

     Symbol Table

     The zval container does not include variable names. Those are stored in what is called a symbol table. In the symbol table our "Reference" section's exmaple looks like:

     symbol | value-------+------a, b | 20-

     So a and b symbols are aliases here. This happens for the scalar types only.

     There are four types of scope in PHP - local, global, static, and function parameters. There is a symbol table for each level of scope. As opposed to scalar values, arrays and objects store their properties in a symbol table of their own. In the symbol table, our "Object Identifiers" section's example looks like:

     $a = new A();$b = $a;-symbol | value object | details-------+--------- -------------+--------a | object(A)#1 object(A)#1 | class A { ... }b | object(A)#1-

     Here a and b symbols are not aliases. They hold a copy of the identifier, which points to the same object.

     References:

     • https://www.php.net/manual/en/features.gc.refcounting-basics.php
     • http://www.levijackson.net/php-zvals-and-symbol-tables/
     • Objects and references in php 5
     • https://github.com/php/php-src/pull/2611
     • https://github.com/php/php-src/commit/5097e2ee13de12b4445b4123e1554c0733c6853c

     Check all answers on Stack Overflow

     1/5

   • What is a "real" programming language?

     Top Answer

     Answered Jul 11, 2010 · 101 votes

     First we need to know what a programming language is. At its minimum, a programming language is something that is read by the computer and instructs it to perform certain operations. Many people would also expect a general purpose programming language to be Turing complete. However there could be situations where a domain-specific language isn't Turing complete but is still a useful programming language for that specific domain. Programming languages can be compiled or interpreted, and they could run on many platforms or just one specific one. Different needs require different programming languages. Clearly PHP is a programming language.

     My definition of "real" programming language would be any programming language that has at least one practical usage in the real world. This is opposed to an esoteric programming language which typically has no practical usage. Since PHP is used widely to solve real problems it easily meets this requirement for being a real programming language, although it is arguably not a particularly beautiful language.

     PHP is a pragmatic language. It was created out of a specific need to be able to quickly make web pages (the name originally stood for Personal Home Pages) and the language was extended as required. Since there was no theoretical background or strong design principles driving its creation (there isn't even a formal specification of the language) it is less clean than many other more modern languages. Features like correct handling of foreign characters / unicode characters are obviously added on afterwards and not cleanly integrated with the rest of the language. This untidiness and lack of theoretical rigour causes many people (especially academics) to dislike the language and this may be part of the reason why your teacher doesn't regard PHP as "real" language.

     However PHP is good at what it was designed for and many sites use it, even very large sites like Facebook, Yahoo! and Wikipedia.

     Other Answers

     Answered Sep 20, 2018 · 58 votes

     It's not compiled

     PHP can be compiled (e.g. through HHVM).

     It's scripted

     That's just another way of saying that PHP is not compiled.

     It doesn't run on every platform

     Neither does Java.

     Sounds like you have a really bad teacher there.

     Other Answers

     Answered Dec 10, 2012 · 34 votes

     Of course PHP is a programming language. He probably meant it isn't a "real" programming language in the same sense that "real" men don't eat quiche.

     Check all answers on Stack Overflow

     2/5

   • What is the best Linux distribution for PHP programming?

     Top Answer

     Answered Feb 14, 2013 · 4 votes

     There is no best. Whichever distribution works for you and maintains the comfort is the best. You can try the popular ones:

     • Ubuntu
     • Fedora
     • OpenSuse

     I personally use, Mint 12

     Check all answers on Stack Overflow

     3/5

   • What is the preferred format to store date/times in a SQL Server database when PHP is your primary language?

     Top Answer

     Answered Oct 22, 2008 · 12 votes

     I would store the dates in the MS-SQL format to assist in using the date manipulation functions in T-SQL to their fullest. It's easier to write and read

     SELECT * FROM FooWHERE DateDiff(d,field1,now()) < 1-

     Than to try and perform the equivalent operation by manipulating integers

     To convert a MsSQL date into a unix timestamp use dateDiff:

     SELECT DATEDIFF(s,'1970-01-01 00:00:00',fieldName) as fieldNameTSFROM TableNameWHERE fieldName between '10/1/2008' and '10/31/2008'-

     To Convert an Unix Timestamp into a MsSQL Date, you can either do it in PHP:

     $msSQLDate = date("Y-m-d H:i:s", $unixDate );-

     or in MsSQL

     INSERT INTO TableName ( fieldName) VALUES ( DATEADD(s,'1970-01-01 00:00:00', ? ) )

     Where parameter one is int($unixDate)

     Check all answers on Stack Overflow

     4/5

   • PHP script language or programming language?

     Top Answer

     Answered Oct 11, 2012 · 9 votes

     Usually a language is called a scripting language if it's not compiled. But these days it doesn't matter anymore - PHP programmer is probably the more accurate term. It's also matters what are you doing with the language. Even people who write in language that have 'script' in its name Java Script are called programmers as soon as they start doing something more advanced than simple DOM manipulations with jquery.

     The only people I've lately heard that refer to them selves as scripters are bash-scripters :)

     Check all answers on Stack Overflow

     5/5

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2. www.tutorialspoint.com › phpPHP Tutorial

   www.tutorialspoint.com › php

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   PHP is a multi-paradigm language that supports imperative, functional, object-oriented, and procedural programming methodologies. PHP is a server-side scripting language that is embedded in HTML. It is used to manage dynamic content, databases, session tracking, even build entire e-commerce sites.

   Code sample

   </head>

   <body>

     <?php echo "Hello, World!";?>

   </body>...

   See more on tutorialspoint

3. www.geeksforgeeks.org › php-tutorialPHP Tutorial - GeeksforGeeks

   www.geeksforgeeks.org › php-tutorial

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   May 10, 2024 · Explore the power of the web with this, free PHP tutorial! We’ll guide you through the essential building blocks, transforming you from a beginner to a confident PHP developer. Get ready to craft dynamic web applications and robust server-side functionality with the versatile PHP language!

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5. www.phptutorial.net › php-tutorial › what-is-phpWhat is PHP? - PHP Tutorial

   www.phptutorial.net › php-tutorial › what-is-php

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