How Does the "&" Operator Work in a PHP Function

How does the & operator work in a PHP function?

The & operator tells PHP not to copy the array when passing it to the function. Instead, a reference to the array is passed into the function, thus the function modifies the original array instead of a copy.

Just look at this minimal example:

<?php
function foo($a) { $a++; }
function bar(&$a) { $a++; }

$x = 1;
foo($x);
echo "$x\n";    
bar($x);
echo "$x\n";
?>

Here, the output is:

1
2

– the call to foo didn’t modify $x. The call to bar, on the other hand, did.

Reference — What does this symbol mean in PHP?

Incrementing / Decrementing Operators

++ increment operator

-- decrement operator

Example    Name              Effect
---------------------------------------------------------------------
++$a       Pre-increment     Increments $a by one, then returns $a.
$a++       Post-increment    Returns $a, then increments $a by one.
--$a       Pre-decrement     Decrements $a by one, then returns $a.
$a--       Post-decrement    Returns $a, then decrements $a by one.

These can go before or after the variable.

If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.

For example:

$apples = 10;
for ($i = 0; $i < 10; ++$i) {
    echo 'I have ' . $apples-- . " apples. I just ate one.\n";
}

Live example

In the case above ++$i is used, since it is faster. $i++ would have the same results.

Pre-increment is a little bit faster because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.

However, you must use $apples--, since first, you want to display the current number of apples, and then you want to subtract one from it.

You can also increment letters in PHP:

$i = "a";
while ($i < "c") {
    echo $i++;
}

Once z is reached aa is next, and so on.

Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

Stack Overflow Posts:

Understanding Incrementing

Why do I have to use the reference operator (&) in a function call?

From the PHP docs

Note: Unlike parameter passing, here you have to use & in both places - to indicate that you want to return by reference, not a copy, and to indicate that reference binding, rather than usual assignment, should be done for $myValue.

http://php.net/manual/en/language.references.return.php

Basically, its to help the php interpreter. The first use in the function definition is to return the reference, and the second is to bind by reference instead of value to the assignment.

By putting the & in the function declaration, the function will return a memory address of the return value. The assignment, when getting this memory address would interpret the value as an int unless explicitly told otherwise, this is why the second & is needed for the assignment operator.

EDIT: As pointed out by @ringø below, it does not return a memory address, but rather an object that will be treated like a copy (technically copy-on-write).

PHP &$string - What does this mean?

You are assigning that array value by reference.

passing argument through reference (&$) and by $ is that when you pass argument through reference you work on original variable, means if you change it inside your function it's going to be changed outside of it as well, if you pass argument as a copy, function creates copy instance of this variable, and work on this copy, so if you change it in the function it won't be changed outside of it

Ref: http://www.php.net/manual/en/language.references.pass.php

PHP: What does a & in front of a variable name mean?

It passes a reference to the variable so when any variable assigned the reference is edited, the original variable is changed. They are really useful when making functions which update an existing variable. Instead of hard coding which variable is updated, you can simply pass a reference to the function instead.

Example

<?php
    $number = 3;
    $pointer = &$number;  // Sets $pointer to a reference to $number
    echo $number."<br/>"; // Outputs  '3' and a line break
    $pointer = 24;        // Sets $number to 24
    echo $number;         // Outputs '24'
?>

CodeIgniter - & operator

As Konrad Rudolph said here: https://stackoverflow.com/a/3957588/837765

The & operator tells PHP not to copy the array when passing it to the
function. Instead, a reference to the array is passed into the
function, thus the function modifies the original array instead of a
copy.

get_config() loads the main config.php file in an array and you modify the returns array directly with the & operator.

It's not a helper. Take a look here (to find the get_config() function) :
http://www.8tiny.com/source/codeigniter/nav.html?_functions/index.html

What does the & sign mean in PHP?

This will force the variable to be passed by reference. Normally, a hard copy would be created for simple types. This can come handy for large strings (performance gain) or if you want to manipulate the variable without using the return statement, eg:

$a = 1;

function inc(&$input)
{
   $input++;
}

inc($a);

echo $a; // 2

Objects will be passed by reference automatically.

If you like to handle a copy over to a function, use

clone $object;

Then, the original object is not altered, eg:

$a = new Obj;
$a->prop = 1;
$b = clone $a;
$b->prop = 2; // $a->prop remains at 1

Using AND/OR in if else PHP statement

Yes. The answer is yes.

http://www.php.net/manual/en/language.operators.logical.php

Two things though:

Many programmers prefer && and || instead of and and or, but they work the same (safe for precedence).
$status = 'clear' should probably be $status == 'clear'. = is assignment, == is comparison.

What does it mean to start a PHP function with an ampersand?

An ampersand before a function name means the function will return a reference to a variable instead of the value.

Returning by reference is useful when
you want to use a function to find to
which variable a reference should be
bound. Do not use return-by-reference
to increase performance. The engine
will automatically optimize this on
its own. Only return references when
you have a valid technical reason to
do so.

See Returning References.

PHP parse/syntax errors; and how to solve them

What are the syntax errors?

PHP belongs to the C-style and imperative programming languages. It has rigid grammar rules, which it cannot recover from when encountering misplaced symbols or identifiers. It can't guess your coding intentions.

Function definition syntax abstract

Most important tips

There are a few basic precautions you can always take:

Use proper code indentation, or adopt any lofty coding style.
Readability prevents irregularities.
Use an IDE or editor for PHP with syntax highlighting.
Which also help with parentheses/bracket balancing.
Read the language reference and examples in the manual.
Twice, to become somewhat proficient.

How to interpret parser errors

A typical syntax error message reads:

Parse error: syntax error, unexpected T_STRING, expecting ';' in file.php on line 217

Which lists the possible location of a syntax mistake. See the mentioned file name and line number.

A moniker such as T_STRING explains which symbol the parser/tokenizer couldn't process finally. This isn't necessarily the cause of the syntax mistake, however.

It's important to look into previous code lines as well. Often syntax errors are just mishaps that happened earlier. The error line number is just where the parser conclusively gave up to process it all.

Solving syntax errors

There are many approaches to narrow down and fix syntax hiccups.

Open the mentioned source file. Look at the mentioned code line.
- For runaway strings and misplaced operators, this is usually where you find the culprit.
- Read the line left to right and imagine what each symbol does.
More regularly you need to look at preceding lines as well.
- In particular, missing ; semicolons are missing at the previous line ends/statement. (At least from the stylistic viewpoint. )
- If { code blocks } are incorrectly closed or nested, you may need to investigate even further up the source code. Use proper code indentation to simplify that.
Look at the syntax colorization!
- Strings and variables and constants should all have different colors.
- Operators +-*/. should be tinted distinct as well. Else they might be in the wrong context.
- If you see string colorization extend too far or too short, then you have found an unescaped or missing closing " or ' string marker.
- Having two same-colored punctuation characters next to each other can also mean trouble. Usually, operators are lone if it's not ++, --, or parentheses following an operator. Two strings/identifiers directly following each other are incorrect in most contexts.
Whitespace is your friend.
Follow any coding style.
Break up long lines temporarily.
- You can freely add newlines between operators or constants and strings. The parser will then concretize the line number for parsing errors. Instead of looking at the very lengthy code, you can isolate the missing or misplaced syntax symbol.
- Split up complex if statements into distinct or nested if conditions.
- Instead of lengthy math formulas or logic chains, use temporary variables to simplify the code. (More readable = fewer errors.)
- Add newlines between:
  1. The code you can easily identify as correct,
  2. The parts you're unsure about,
  3. And the lines which the parser complains about.
  Partitioning up long code blocks really helps to locate the origin of syntax errors.
Comment out offending code.
- If you can't isolate the problem source, start to comment out (and thus temporarily remove) blocks of code.
- As soon as you got rid of the parsing error, you have found the problem source. Look more closely there.
- Sometimes you want to temporarily remove complete function/method blocks. (In case of unmatched curly braces and wrongly indented code.)
- When you can't resolve the syntax issue, try to rewrite the commented out sections from scratch.
As a newcomer, avoid some of the confusing syntax constructs.
- The ternary ? : condition operator can compact code and is useful indeed. But it doesn't aid readability in all cases. Prefer plain if statements while unversed.
- PHP's alternative syntax (if:/elseif:/endif;) is common for templates, but arguably less easy to follow than normal { code } blocks.
The most prevalent newcomer mistakes are:
- Missing semicolons ; for terminating statements/lines.
- Mismatched string quotes for " or ' and unescaped quotes within.
- Forgotten operators, in particular for the string . concatenation.
- Unbalanced ( parentheses ). Count them in the reported line. Are there an equal number of them?
Don't forget that solving one syntax problem can uncover the next.
- If you make one issue go away, but other crops up in some code below, you're mostly on the right path.
- If after editing a new syntax error crops up in the same line, then your attempted change was possibly a failure. (Not always though.)
Restore a backup of previously working code, if you can't fix it.
- Adopt a source code versioning system. You can always view a diff of the broken and last working version. Which might be enlightening as to what the syntax problem is.
Invisible stray Unicode characters: In some cases, you need to use a hexeditor or different editor/viewer on your source. Some problems cannot be found just from looking at your code.
- Try grep --color -P -n "\[\x80-\xFF\]" file.php as the first measure to find non-ASCII symbols.
- In particular BOMs, zero-width spaces, or non-breaking spaces, and smart quotes regularly can find their way into the source code.
Take care of which type of linebreaks are saved in files.
- PHP just honors \n newlines, not \r carriage returns.
- Which is occasionally an issue for MacOS users (even on OS X for misconfigured editors).
- It often only surfaces as an issue when single-line // or # comments are used. Multiline /*...*/ comments do seldom disturb the parser when linebreaks get ignored.
If your syntax error does not transmit over the web:
It happens that you have a syntax error on your machine. But posting the very same file online does not exhibit it anymore. Which can only mean one of two things:
- You are looking at the wrong file!
- Or your code contained invisible stray Unicode (see above).
  You can easily find out: Just copy your code back from the web form into your text editor.
Check your PHP version. Not all syntax constructs are available on every server.
- php -v for the command line interpreter
- <?php phpinfo(); for the one invoked through the webserver.
Those aren't necessarily the same. In particular when working with frameworks, you will them to match up.
Don't use PHP's reserved keywords as identifiers for functions/methods, classes or constants.
Trial-and-error is your last resort.

If all else fails, you can always google your error message. Syntax symbols aren't as easy to search for (Stack Overflow itself is indexed by SymbolHound though). Therefore it may take looking through a few more pages before you find something relevant.

Further guides:

PHP Debugging Basics by David Sklar
Fixing PHP Errors by Jason McCreary
PHP Errors – 10 Common Mistakes by Mario Lurig
Common PHP Errors and Solutions
How to Troubleshoot and Fix your WordPress Website
A Guide To PHP Error Messages For Designers - Smashing Magazine

White screen of death

If your website is just blank, then typically a syntax error is the cause.
Enable their display with:

error_reporting = E_ALL
display_errors = 1

In your php.ini generally, or via .htaccess for mod_php,
or even .user.ini with FastCGI setups.

Enabling it within the broken script is too late because PHP can't even interpret/run the first line. A quick workaround is crafting a wrapper script, say test.php:

<?php
   error_reporting(E_ALL);
   ini_set("display_errors", 1);
   include("./broken-script.php");

Then invoke the failing code by accessing this wrapper script.

It also helps to enable PHP's error_log and look into your webserver's error.log when a script crashes with HTTP 500 responses.

How Does the "&" Operator Work in a PHP Function