SunshinePHP Developer Conference 2015

gmp_strval

(PHP 4 >= 4.0.4, PHP 5)

gmp_strvalConvert 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));
?>

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User Contributed Notes 3 notes

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0
russell dot s dot harper at gmail dot com
4 years ago
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.
up
0
php at richardneill dot org
8 years ago
I think it's no longer necessary to worry about trailing nulls. This was fixed in Feb 2002 (see bug 10133)
up
0
caldwell at utm dot NoSpamPlease dot edu
13 years ago
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!).
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