Top php frequently asked interview questions
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?
Source: (StackOverflow)
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:
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)
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
Source: (StackOverflow)