I think it's no longer necessary to worry about trailing nulls. This was fixed in Feb 2002 (see bug 10133)
gmp_strval
(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)
gmp_strval — Convierte un número GMP a cadena
Descripción
Convierte un número GMP a la representación de cadena en base
base. La base por defecto es 10.
Parámetros
-
gmpnumber -
El número GMP a convertir en cadena.
resource de número de GMP en PHP 5.5 y anterior, o un objeto de GMP en PHP 5.6 y posterior, o un string numérico siempre que sea posible convertirlo a un número.
-
base -
La base del número retornado. La base por defecto es 10. Los valores permitidos para la base son de 2 a 62 y -2 a -36.
Valores devueltos
El número, como una string.
Historial de cambios
| Versión | Descripción |
|---|---|
| 5.3.2 |
La base fue extendida de 2 a 36, a
2 a 62 y -2 a -36.
|
Notas
Nota:
To use the extended base introduced in PHP 5.3.2, then PHP must be compiled against GMP 4.2.0 or greater.
Ejemplos
Ejemplo #1 Converting a GMP number to a string
<?php
$a = gmp_init("0x41682179fbf5");
printf("Decimal: %s, base 36: %s", gmp_strval($a), gmp_strval($a,36));
?>
add a note
User Contributed Notes 5 notes
php at richardneill dot org ¶
18 years ago
Nitrogen ¶
9 years ago
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.
russell dot s dot harper at gmail dot com ¶
14 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.
caldwell at utm dot NoSpamPlease dot edu ¶
23 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!).
