gmp_strval

(PHP 4 >= 4.0.4, PHP 5, PHP 7)

gmp_strval — Convert GMP number to string

说明

string gmp_strval ( GMP $gmpnumber [, int $base = 10 ] )

Convert GMP number to string representation in base base. The default base is 10.

参数

gmpnumber

The GMP number that will be converted to a string.

可以是一个 GMP 数据 resouce ，或一个可以转换为数值的字符串。

base

The base of the returned number. The default base is 10. Allowed values for the base are from 2 to 62 and -2 to -36.

返回值

The number, as a string .

更新日志

版本	说明
5.3.2	The `base` was extended from 2 to 36, to 2 to 62 and -2 to -36.

注释

Note:

To use the extended base introduced in PHP 5.3.2, then PHP must be compiled against GMP 4.2.0 or greater.

范例

Example #1 Converting a GMP number to a string

  <?php
$a  =  gmp_init ( "0x41682179fbf5" );
 printf ( "Decimal: %s, 36-based: %s" ,  gmp_strval ( $a ),  gmp_strval ( $a , 36 ));
 ?>

用户评论:

[#1] Nitrogen [2015-11-29 23:56:30]

It may be worth noting that using gmp_strval can slow your script down a lot with large numbers.

This script for example, produces factorials in succession:
<?php $start = microtime(TRUE); $fact = gmp_init(1, 10); for($i=1;$i<100000;$i++) { // calculates 100,000 factorials $fact = gmp_mul($fact, $i); // $fact is now the result of the $ith factorial // gmp_strval($fact, 10); // see below... if(microtime(TRUE)-$start>1) // stop calculating after 1 second break; } // print whatever result that took 1 second to complete printf("\$i = %d\n\$fact = %s\n", gmp_strval($fact, 10)); ?>

My server calculates around about the 69,500th factorial on average every time. Uncommenting that gmp_strval line slows this process down dramatically, and only calculates about 5,000 factorials. This is about 14 times longer than before (this is consistent with allowing it to run for any number of seconds, not just 1).

Nitrogen.

[#2] russell dot s dot harper at gmail dot com [2010-05-26 10:22:19]

A gotcha when using the value from gmp_strval as a key in an associative array. Some numbers are 2^31 are converted to signed integer format, this is usually incorrect.

<?php $a = gmp_init('2147483649'); // = 2^31 + 1 $b = gmp_init('3173604585'); // = 2^31 < $b < 2^32 $c = gmp_strval($a); $d = gmp_strval($b); $e = array($c => 'c', $d => 'd'); print '*** Expect '."\n"; print 'Array '."\n".'('."\n".'    ['.$c.'] => c'."\n".'    ['.$d.'] => d'."\n".')'."\n\n"; print '*** Actual '."\n"; print_r($e); ?>

Output:

*** Expect
Array
(
    [2147483649] => c
    [3173604585] => d
)

*** Actual
Array
(
    [-2147483647] => c
    [3173604585] => d
)

A workaround is to format as base 16 and append '0x' before using as a key.

[#3] php at richardneill dot org [2006-09-19 16:47:57]

I think it's no longer necessary to worry about trailing nulls. This was fixed in Feb 2002 (see bug 10133)

[#4] caldwell at utm dot NoSpamPlease dot edu [2001-07-22 08:17:20]

Warning: gmp_strval may return a null terminated string (e.g., gmp_strval(gmp_init(8)) has two characters. This is because gmp is built for speed, so uses estimates based on things it can get quickly, like the number of bits in N. So since 8 is a 4 bit number, it will be allocated ceil(log10(2^4))=ceil(4*0.30103....) = 2 characters. The gmp folks feel it is the caller's responsibility (in this case the PHP interface) to check whether or not all the characters were required. PHP might have done this for us (and may in the future), but for now, you need to check (if it matters to you--it sure did in my program!).