What code is this?

Question

Please consider the following code snippet:

From php-5.3.1/ext/session/session.c:

PHPAPI char *php_session_create_id(PS_CREATE_SID_ARGS)
…
gettimeofday(&tv, NULL);
…
/* maximum 15+19+19+10 bytes */
spprintf(&buf, 0, "%.15s%ld%ld%0.8F", remote_addr ? 
remote_addr : "", tv.tv_sec, (long int)tv.tv_usec, 
php_combined_lcg(TSRMLS_C) * 10);
…
return buf;
}

I have found it on the internet. But I can't understand what code is this. I guess this is the implementation of a php function in C++. If yes, then please explain me how php calles c++ function in it?

PHP is interpreted and ends up running as machine code. The interpreter is written in C :-) — Gunther Piez, Feb 09 '11 at 13:22
Chris: You are wrong See: http://stackoverflow.com/questions/2720488/how-exactly-is-a-php-script-executed — Mchl, Feb 09 '11 at 13:25

score 4 · Accepted Answer · answered Feb 09 '11 at 13:10

4

The shocking truth is that PHP is written in C. You are looking at the source of PHP itself, or need to explain the question further.

answered Feb 09 '11 at 13:10

Marco Mariani

13,556
6
39
55

What does it mean that php is written in C? Does each function of php implemented with the same name in C, and when you call a php function the C function is being called itself? Can I say that PHP is a lib written in C and when I write PHP, actually I write C by using PHP library? – Narek Feb 09 '11 at 13:14
@Narek The PHP interpreter is a program, which is written in C. You might want to google "interpreter" to understand what that is. – Jim Balter Feb 09 '11 at 13:24
@Narek: See http://stackoverflow.com/questions/2720488/how-exactly-is-a-php-script-executed – Mchl Feb 09 '11 at 13:26
No. When you write PHP, your code is being interpreted by the PHP interpreter. This interpreter happens to be written in a different language - C - but which language actually doesn't matter for you. An PHP interpreter could even be written in Java or Assembler. That a lot of PHP function names resemble C standard library function names is a coincidence. – Gunther Piez Feb 09 '11 at 13:30
1

There is in fact a PHP implementation written in Java: http://www.caucho.com/resin-3.0/quercus/ – Mchl Feb 09 '11 at 13:37

score 4 · Answer 2 · answered Feb 09 '11 at 13:12

It is not a C++ code, it is pure C. The PHP library can call C functions just like any other library implemented in C. The code snippet generates a "unique" session ID consisting of the client address, the current time, and a pseudo-random number from some linear congruential generator.

Shinnok · Answer 3 · 2011-02-09T13:54:33.210

I am guessing that you ended up to that piece of code via the DEFCON 18: How I Met Your Girlfriend lecture? Great talk btw. :-)

Now about the code snippet, it is C and it is part of PHP's code. This exact function handles the generation of PHP session ids. You have the entire function logic explained in the lecture i mentioned above, in case you didn't see it.

As a side not, PHP does not call C functions, instead you call a PHP library function and so it happens that most of those functions are written in C and exposed through PHP. On the other hand php_session_create_id does not have an equivalent exposed to PHP, since that one is used internally by PHP when you start a session using PHP session api.

What code is this?

3 Answers3