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Delete an element from an array

Is there an easy way to delete an element from a PHP array, such that foreach ($array) no longer includes that element?

I thought that setting it to null would do it, but apparently not.

How 'foreach' actually works

Let me prefix this by saying that I know what foreach is, does and how to use it. This question concerns how it works under the bonnet, and I don't want any answers along the lines of "this is how you loop an array with foreach".

For a long time I assumed that foreach worked with the array itself. Then I found many references to the fact that it works with a copy of the array, and I have since assumed this to be the end of the story. But I recently got into a discussion on the matter, and after a little experimentation found that this was not in fact 100% true.

Let me show what I mean. For the following test cases, we will be working with the following array:

$array = array(1, 2, 3, 4, 5);

Test case 1:

foreach ($array as $item) {
  echo "$item\n";
  $array[] = $item;
}
print_r($array);

/* Output in loop:    1 2 3 4 5
   $array after loop: 1 2 3 4 5 1 2 3 4 5 */

This clearly shows that we are not working directly with the source array - otherwise the loop would continue forever, since we are constantly pushing items onto the array during the loop. But just to be sure this is the case:

Test case 2:

foreach ($array as $key => $item) {
  $array[$key + 1] = $item + 2;
  echo "$item\n";
}

print_r($array);

/* Output in loop:    1 2 3 4 5
   $array after loop: 1 3 4 5 6 7 */

This backs up our initial conclusion, we are working with a copy of the source array during the loop, otherwise we would see the modified values during the loop. But...

If we look in the manual, we find this statement:

When foreach first starts executing, the internal array pointer is automatically reset to the first element of the array.

Right... this seems to suggest that foreach relies on the array pointer of the source array. But we've just proved that we're not working with the source array, right? Well, not entirely.

Test case 3:

// Move the array pointer on one to make sure it doesn't affect the loop
var_dump(each($array));

foreach ($array as $item) {
  echo "$item\n";
}

var_dump(each($array));

/* Output
  array(4) {
    [1]=>
    int(1)
    ["value"]=>
    int(1)
    [0]=>
    int(0)
    ["key"]=>
    int(0)
  }
  1
  2
  3
  4
  5
  bool(false)
*/

So, despite the fact that we are not working directly with the source array, we are working directly with the source array pointer - the fact that the pointer is at the end of the array at the end of the loop shows this. Except this can't be true - if it was, then test case 1 would loop forever.

The PHP manual also states:

As foreach relies on the internal array pointer changing it within the loop may lead to unexpected behavior.

Well, let's find out what that "unexpected behavior" is (technically, any behavior is unexpected since I no longer know what to expect).

Test case 4:

foreach ($array as $key => $item) {
  echo "$item\n";
  each($array);
}

/* Output: 1 2 3 4 5 */

Test case 5:

foreach ($array as $key => $item) {
  echo "$item\n";
  reset($array);
}

/* Output: 1 2 3 4 5 */

...nothing that unexpected there, in fact it seems to support the "copy of source" theory.

The Question

What is going on here? My C-fu is not good enough for me to able to extract a proper conclusion simply by looking at the PHP source code, I would appreciate it if someone could translate it into English for me.

It seems to me that foreach works with a copy of the array, but sets the array pointer of the source array to the end of the array after the loop.

• Is this correct and the whole story?
• If not, what is it really doing?
• Is there any situation where using functions that adjust the array pointer (each(), reset() et al.) during a foreach could affect the outcome of the loop?

How to fix "Headers already sent" error in PHP

When running my script, I am getting several errors like this:

Warning: Cannot modify header information - headers already sent by (output started at /some/file.php:12) in /some/file.php on line 23

The lines mentioned in the error messages contain header() and setcookie() calls.

What could be the reason for this? And how to fix it?

Using a regular expression to validate an email address

Over the years I have slowly developed a regular expression that validates MOST email addresses correctly, assuming they don't use an IP address as the server part.

I use it in several PHP programs, and it works most of the time. However, from time to time I get contacted by someone that is having trouble with a site that uses it, and I end up having to make some adjustment (most recently I realized that I wasn't allowing 4-character TLDs).

What's the best regular expression you have or have seen for validating emails?

I've seen several solutions that use functions that use several shorter expressions, but I'd rather have one long complex expression in a simple function instead of several short expression in a more complex function.

Secure hash and salt for PHP passwords

It is currently said that MD5 is partially unsafe. Taking this into consideration, I'd like to know which mechanism to use for password protection.

This question, Is “double hashing” a password less secure than just hashing it once? suggests that hashing multiple times may be a good idea, whereas How to implement password protection for individual files? suggests using salt.

I'm using PHP. I want a safe and fast password encryption system. Hashing a password a million times may be safer, but also slower. How to achieve a good balance between speed and safety? Also, I'd prefer the result to have a constant number of characters.

1. The hashing mechanism must be available in PHP
2. It must be safe
3. It can use salt (in this case, are all salts equally good? Is there any way to generate good salts?)

Also, should I store two fields in the database (one using MD5 and another one using SHA, for example)? Would it make it safer or unsafer?

In case I wasn't clear enough, I want to know which hashing function(s) to use and how to pick a good salt in order to have a safe and fast password protection mechanism.

Related questions that don't quite cover my question:

What's the difference between SHA and MD5 in PHP
Simple Password Encryption
Secure methods of storing keys, passwords for asp.net
How would you implement salted passwords in Tomcat 5.5

Sort Multi-dimensional Array by Value [duplicate]

Possible Duplicate:
How do I Sort a Multidimensional Array in PHP

How can I sort this array by the value of the "order" key? Even though the values are currently sequential, they will not always be.

Array
(
    [0] => Array
        (
            [hashtag] => a7e87329b5eab8578f4f1098a152d6f4
            [title] => Flower
            [order] => 3
        )

    [1] => Array
        (
            [hashtag] => b24ce0cd392a5b0b8dedc66c25213594
            [title] => Free
            [order] => 2
        )

    [2] => Array
        (
            [hashtag] => e7d31fc0602fb2ede144d18cdffd816b
            [title] => Ready
            [order] => 1
        )
)

Why shouldn't I use mysql_* functions in PHP?

What are the technical reasons why I shouldn't use mysql_* functions? (e.g. mysql_query(), mysql_connect() or mysql_real_escape_string())?

Why should I use something else even if they work on my site?

How do you parse and process HTML/XML in PHP?

How can one parse HTML/XML and extract information from it?

This is a General Reference question for the php tag

When to use self vs $this?

In PHP 5, what is the difference between using self and $this?

When is each appropriate?

Reference - What does this symbol mean in PHP?

What is this?

This is a collection of questions that come up every now and then about syntax in PHP. This is also a Community Wiki, so everyone is invited to participate in maintaining this list.

Why is this?

It used to be hard to find questions about operators and other syntax tokens.¹
The main idea is to have links to existing questions on Stack Overflow, so it's easier for us to reference them, not to copy over content from the PHP Manual.

¹ Note: Since January 2013, Stack Overflow does support special characters. Just surround the search terms by quotes, e.g. [php] "==" vs "==="

What should I do here?

If you have been pointed here by someone because you have asked such a question, please find the particular syntax below. The linked pages to the PHP manual along with the linked questions will likely answer your question then. If so, you are encouraged to upvote the answer. This list is not meant as a substitute to the help others provided.

The List

If your particular token is not listed below, you might find it in the List of Parser Tokens.

& Bitwise Operators or References

• What does it mean to start a PHP function with an ampersand?
• Understanding PHP & (ampersand, bitwise and) operator
• PHP "&" operator
• difference between & and && in PHP
• What does "&" mean here in PHP?
• what does & mean in this case?
• What does the & sign mean in PHP?
• What does this signature mean(&) in PHP?
• How does "&" operator work in PHP function?
• What does & in &2 mean in PHP?
• When should I use Bitwise operator?
• Is there ever a need to use ampersand in front of an object

=& References

• Reference assignment operator in php =&
• what do "=&" / "&=" operators in php mean?
• What do the '&=' and '=&' operators do?
• What does =& mean in PHP?

&= Bitwise Operators

• what do "=&" / "&=" operators in php mean?
• What do the '&=' and '=&' operators do?

&& Logical Operators

• 'AND' vs '&&' as operator
• difference between & and && in PHP
• PHP: Is there a difference between operators AND and && here?
• PHP - and / or keywords

% Arithmetic Operators

• What does the percent sign mean in PHP?
• What is the PHP operator % and how to use it in real world examples?

!! Logical Operators

• Double Not (!!) Operator in PHP

@ Error Control Operators

• What is the use of @ symbol in php?
• PHP - 'At' symbol before variable name: @$_POST
• PHP functions and @functions
• Should I use @ in my PHP code?

?: Ternary Operator

• What is ?: in PHP 5.3?
• What is the PHP ? : operator called and what does it do?
• ?: operator (the 'Elvis operator') in PHP
• Where can I read about conditionals done with ? and :
• Using PHP 5.3 ?: operator

?? Null Coalesce Operator (since PHP 7)

• C#'s null coalescing operator (??) in PHP?

: Alternative syntax for control structures, Ternary Operator

• What is this : in php?
• What does this ":" mean in PHP?

:: Scope Resolution Operator

• What do two colons mean in PHP?
• What's the meaning of the PHP Token Name T_PAAMAYIM_NEKUDOTAYIM
• What's the difference between :: (double colon) and -> (arrow) in PHP?
• What exactly are late static bindings in PHP?
• static::staticFunctionName()
• Unexpected T_PAAMAYIM_NEKUDOTAYIM, expecting T_NS_Separator

\ Namespaces

• Backslash in PHP -- what does it mean?
• What does a \ (backslash) do in PHP (5.3+)?

-> Classes And Objects

• What is the "->" PHP operator called and how do you say it when reading code out loud?
• where we use object operator "->" in php
• What's the difference between :: (double colon) and -> (arrow) in PHP?
• What does this PHP syntax mean: $var1->$var2
• Absolutely basic PHP question about the "-> " syntax

=> Arrays

• What does "=>" mean in PHP?
• Use of => in PHP
• What does $k => $v in foreach($ex as $k=>$v) mean?

^ Bitwise Operators

• How does the bitwise operator XOR ('^') work?
• What does ^ mean in PHP?

>> Bitwise Operators

• What does >> mean in PHP?

<< Bitwise Operators

• Strange print behaviour in PHP?

<<< Heredoc or Nowdoc

• What does <<<END mean in PHP?
• PHP <<<EOB
• In PHP, what does "<<<" represent?
• Using <<<CON in PHP
• What's this kind of syntax in PHP?

= Assignment Operators

• The 3 different equals

== Comparison Operators

• php == vs === operator
• How do the PHP equality (== double equals) and identity (=== triple equals) comparison operators differ?
• PHP != and == operators
• The 3 different equals
• PHP Type-Juggling and (strict) Greater/Lesser Than Comparisons

=== Comparison Operators

• What does "===" mean?
• php == vs === operator
• How do the PHP equality (== double equals) and identity (=== triple equals) comparison operators differ?
• The 3 different equals
• PHP Type-Juggling and (strict) Greater/Lesser Than Comparisons

!== Comparison Operators

• What does !== comparison operator in PHP mean?
• Is there a difference between !== and != in PHP?

!= Comparison Operators

• PHP != and == operators
• Is there a difference between !== and != in PHP?
• comparing, !== versus !=
• What is the difference between <> and !=

<> Comparison Operators

• php operator <>
• php <> operator
• What is the difference between <> and !=
• PHP Type-Juggling and (strict) Greater/Lesser Than Comparisons

<=> Comparison Operators

• Spaceship (three way comparison) operator

| Bitwise Operators

• What is the difference between the | and || operators?
• What Does Using A Single Pipe '|' In A Function Argument Do?

|| Logical Operators

• What is the difference between the | and || operators?
• PHP - and / or keywords
• What exactly does || mean?
• The behaviour of the or operator in PHP

~ Bitwise Operators

• What does this ~ operator mean here?

+ Arithmetic Operators, Array Operators

• + operator for array in PHP?

+= Assignment Operators

• What is += used for?
• What does `$page -= 1` in my PHP document mean?

++ Incrementing/Decrementing Operators

• Understanding Incrementing
• Answer below

.= Assignment Operators

• What is the difference between .= and += in php
• To understand a line of PHP

. String Operators

• Difference between "," and "." in PHP?
• What does a . (dot) do in PHP?

, Function Arguments

• Difference between "," and "." in PHP?

$$ Variable Variables

• What does $$ mean in PHP?
• what is "$$" in PHP
• $function() and $$variable

` Execution Operator

• What are the backticks `` called?

<?= Short Open Tags

• What does this symbol mean in PHP <?=
• What does '<?=' mean in PHP?
• What does <?= mean?

[] Arrays

• PHP arrays... What is/are the meaning(s) of an empty bracket?
• PHP : What is the meaning of []
• Php array_push() vs myArray[]
• What does [] mean when reading from a php array?
• Shorthand for arrays: literal $var = [] empty array

<? Opening and Closing tags

• Are PHP short tags acceptable to use?

... Argument unpacking (since PHP 5.6)

** Exponentiation (since PHP 5.6)

# One-line shell-style comment

• What does # mean in PHP?
• Can I use hashes for comments in PHP?

I never really understood: what is CGI?

CGI is a Common Gateway Interface. As the name says, it is a "common" gateway interface for everything. It is so trivial and naive from the name. I feel that I understood this and I felt this every time I encountered this word. But frankly, I didn't. I'm still confused.

I am a PHP programmer. I did lot of web development.

user (client) request for page ---> webserver(->embedded PHP interpreter) ----> Server side(PHP) Script ---> MySQL Server.

Now say my PHP Script can fetch results from MySQL Server && MATLAB Server && Some other server.

So, now PHP Script is the CGI? because its interface for the between webserver & All other servers? I don't know. Sometimes they call CGI, a technology & othertimes they call CGI a program or someother server.

• What exactly is CGI?

• Whats the big deal with /cgi-bin/*.cgi? What's up with this? I don't know what is this cgi-bin directory on the server for. I don't know why they have *.cgi extensions.

• Why does Perl always comes in the way. CGI & Perl (language). I also don't know what's up with these two. Almost all the time I keep hearing these two in combination "CGI & Perl". This book is another great example CGI Programming with Perl. Why not "CGI Programming with PHP/JSP/ASP"? I never saw such things.

• CGI Programming in C, confuses me a lot. "in C"?? Seriously?? I don't know what to say. I'm just confused. "in C"?? This changes everything. Program needs to be compiled and executed. This entirely changes my view of web programming. When do I compile? How does the program gets executed (because it will be a machine code, so it must execute as a independent process). How does it communicate with the web server? IPC? and interfacing with all the servers (in my example MATLAB & MySQL) using socket programming? I'm lost!!

• They say that CGI is depreciated. Its no more in use. Is it so? What is its latest update?

Once, I ran into a situation where I had to give HTTP PUT request access to web server (Apache HTTPD). Its a long back. So, as far as I remember this is what I did:

1. Edited the configuration file of Apache HTTPD to tell webserver to pass all HTTP PUT requests to some put.php ( I had to write this PHP script)

2. Implement put.php to handle the request (save the file to the location mentioned)

People said that I wrote a CGI Script. Seriously, I didn't have a clue what they were talking about.

• Did I really write CGI Script?

I hope you understood what my confusion is. (Because I myself don't know where I'm confused). I request you guys to keep your answer as simple as possible. I really can't understand any fancy technical terminology. At least not in this case.

EDIT:

I found this amazing tutorial "CGI Programming Is Simple!" - CGI Tutorial, which explains the concepts in simplest possible way. After reading this article you may want to read Getting Started with CGI Programming in C to supplement your understanding with actual code samples. I've also added these links to this tutorial to Wikipedia's article : http://en.wikipedia.org/wiki/Common_Gateway_Interface

PHP: Public, Private, Protected

When and why should I use and what's the difference between, public, private and protected functions/variables inside a class?

Examples:

// Public
public $variable;
public function doSomething(){
    ...code...
}

// Private
private $variable;
private function doSomething(){
    ...code...
}

// Protected
protected $variable;
protected function doSomething(){
    ...code...
}

What is thread safe or non thread safe in PHP

I saw different binaries for PHP, like non thread or thread safe? What does this mean? What is the difference between these packages?

How to get the client IP address in PHP?

How can I get the client IP address using PHP?

I want to keep record of the user who logged into my website through his/her IP address.

Reference - What does this error mean in PHP?

What is this?

This is a number of answers about warnings, errors and notices you might encounter while programming PHP and have no clue how to fix. This is also a Community Wiki, so everyone is invited to participate in adding to and maintaining this list.

Why is this?

Questions like "Headers already sent" or "Calling a member of a non-object" pop up frequently on Stack Overflow. The root cause of those questions is always the same. So the answers to those questions typically repeat them and then show the OP which line to change in his/her particular case. These answers do not add any value to the site because they only apply to the OP's particular code. Other users having the same error can not easily read the solution out of it because they are too localized. That is sad, because once you understood the root cause, fixing the error is trivial. Hence, this list tries to explain the solution in a general way to apply.

What should I do here?

If your question has been marked as a duplicate of this, please find your error message below and apply the fix to your code. The answers usually contain further links to investigate in case it shouldn't be clear from the general answer alone.

If you want to contribute, please add your "favorite" error message, warning or notice, one per answer, a short description what it means (even if it is only highlighting terms to their manual page), a possible solution or debugging approach and a listing of existing Q&A that are of value. Also, feel free to improve any existing answers.

The List

• Nothing is seen. The page is empty and white. (also known as White Page/Screen Of Death)
• Code doesn't run/what looks like parts of my PHP code are output
• Warning: Cannot modify header information - headers already sent
• Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given a.k.a.
  Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource a.k.a.
  Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given (or similar variations)
• Warning: [function] expects parameter 1 to be resource, boolean given
• Warning: [function]: failed to open stream: [reason]
• Warning: open_basedir restriction in effect
• Warning: Division by zero
• Warning: Illegal string offset 'XXX'
• Parse error: syntax error, unexpected '['
• Parse error: syntax error, unexpected T_XXX
• Parse error: syntax error, unexpected T_ENCAPSED_AND_WHITESPACE
• Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM
• Parse error: syntax error, unexpected T_VARIABLE
• Fatal error: Allowed memory size of XXX bytes exhausted (tried to allocate XXX bytes)
• Fatal error: Call to a member function ... on a non-object
• Fatal Error: Call to Undefined function XXX
• Fatal Error: Cannot redeclare XXX
• Fatal error: Can't use function return value in write context
• Fatal error: Declaration of AAA::BBB() must be compatible with that of CCC::BBB() '
• Fatal error: Using $this when not in object context
• Notice: Array to string conversion
• Notice: Trying to get property of non-object error
• Notice: Undefined variable
• Notice: Undefined Index
• Notice: Uninitialized string offset: X
• Notice: Use of undefined constant XXX - assumed 'XXX'
• MySQL: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ... at line ...
• Strict Standards: Non-static method [<class>::<method>] should not be called statically

Also see

• Reference - What does this symbol mean in PHP?