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Bug #49636 PHP_INT_SIZE inconsistent with pack("i")
Submitted: 2009-09-23 01:54 UTC Modified: 2009-10-02 10:51 UTC
From: hsu at jean-david dot com Assigned:
Status: Closed Package: Strings related
PHP Version: 5.2.11 OS: linux
Private report: No CVE-ID: None
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 [2009-09-23 01:54 UTC] hsu at jean-david dot com 
Description:
------------
PHP pack documentation:
i  	signed integer (machine dependent size and byte order)

PHP integer documentation:
Integer size can be determined using the constant PHP_INT_SIZE

On some systems, I believe that the word "integer" will refer to objects of different sizes, such that pack("i", _) could point to an object of size X bytes and PHP_INT_SIZE return value Y which is inconsistent.

/main/main.c l.1796:
REGISTER_MAIN_LONG_CONSTANT("PHP_INT_SIZE", sizeof(long), CONST_PERSISTENT | CONST_CS);

/ext/standard/pack.c l.402-403:
php_pack(argv[currentarg++], sizeof(int), int_map, &output[outputpos]);
outputpos += sizeof(int);

Reproduce code:
---------------
file_put_contents("test.bin",pack("I", 2));
var_dump(PHP_INT_SIZE === filesize("test.bin"));

Expected result:
----------------
bool(true)

Actual result:
--------------
bool(false)

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 [2009-09-23 07:28 UTC] sjoerd@php.net 
Thank you for your bug report.

The integer in the pack documentation and the integer in the PHP integer documentation refer to different things. The pack integer is a C-style int. The PHP integer is implemented in a long. These do not need to be the same size.
 [2009-09-24 10:41 UTC] hsu at jean-david dot com 
There is no easy way to pack a plain old php integer
This means that pack has many different format codes but none for a php int?
 [2009-10-01 11:35 UTC] sjoerd@php.net 
Correct. You can assume that an PHP int is always 32 bits and use l for pack. However, pack() is probably the wrong tool for the thing you want to do.

The pack() function is mainly useful to interoperate with other programs or protocols. In that case, you typically know the format and sizes of things you want to pack.

If there were a pack format character which is exactly the size of a PHP int, this would mean only PHP with the same int size could read it. If you want to store and retrieve data using only PHP, you are better off using serialize().

Is this clear, and do you consider this bug solved?
 [2009-10-02 10:51 UTC] hsu at jean-david dot com 
"If there were a pack format character which is exactly the size of a PHP int, this would mean only PHP with the same int size could read it"
This is also true with the "i" format.

The reason that I use pack is to manipulate bit streams in PHP, but yes, I would use serialize to just store an int.
You are right, there is no big inconvenience using the "l" format and  it's fixed size.

I did not know that it was a design choice not to have a format character for a PHP int.
Yes, please mark this bug as solved.
Thank you for the explanation.
 
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