PHP: How to convert bigint from int to string?

Question

I want to be able to convert big ints into their full string derivatives.

For example.

$bigint = 9999999999999999999;
$bigint_string = (string) $bigint;
var_dump($bigint_string);

outputs

string(7) "1.0e+19"

but i need

string(19) "9999999999999999999"

Please don't tell me that I should just originally set the $bigint value as a string. That is not an option. I really am stuck and don't know if it is even possible?

Precision has been lost. That's out of range for a float. You won't get the string output you want. — mario, Aug 22 '11 at 17:38
I guess the only way really is to initially cast as a string. balls. — buggedcom, Aug 22 '11 at 17:48
Might have gotten more relevant answers if you explained the use case rather than what think you want. — mario, Aug 22 '11 at 17:49
@hakre - sorry. I did not realise that the big int would be a float. I've never dealt with numbers this large before. — buggedcom, Aug 22 '11 at 17:58

hakre · Accepted Answer · 2011-08-22T17:55:28.353

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You actually should ensure that you type what you mean:

$bigint = 9999999999999999999;

Is not a PHP integer but float:

float(1.0E+19)

If you would have done

$bigint = (int) 9999999999999999999;

You would have set an integer in fact, but it would not be the number you might have expected:

int(-8446744073709551616)

It's no problem at all to turn that into string as you might have guessed. So take care when you write numbers into code that you actually write what you mean.

See this line again:

$bigint = 9999999999999999999;

try to understand what you have actually written. It's not an integer at all because PHP will turn it into a float. See Example #4 Integer overflow on a 64-bit system in the integer manual page.

If you need higher precision, checkout GNU Multiple Precision, it might have what you're looking for. However, this won't change how to write numbers in PHP:

$bigint = gmp_init("9999999999999999999");
$bigint_string = gmp_strval($bigint);
var_dump($bigint, $bigint_string);

Output:

resource(4) of type (GMP integer)
string(19) "9999999999999999999"

edited Aug 22 '11 at 17:55

answered Aug 22 '11 at 17:48

hakre

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Thanks hakre for the in-depth response. I guess I have got plenty more to learn. – buggedcom Aug 22 '11 at 17:56
gmp_init() needs to start with a string or an int -- not a float. Which means, if you've already got it in a string or an int, you don't need gmp. – Alex Howansky Aug 22 '11 at 17:59
@buggedcom: You're welcome. There is always something new to learn ;) – hakre Aug 22 '11 at 18:06
this doesn't work if you pass it like this: $bigint = gmp_init(9999999999999999999); – Phill Pafford Nov 04 '11 at 15:13
@PhillPafford: Pass the number as integer or string, not float. – hakre Nov 05 '11 at 06:25
@Alex Howansky: Well, you can't do integer operations with strings in PHP if they are above PHP's integer limit, but gmp can. – hakre Nov 05 '11 at 06:28
@hakre: Yes, but there's a catch-22 here. In this particular question, the OP isn't doing operations, he simply wants a string representation of a big int. He would have to pass a string to gmp_init() to get it. Which means he'd have to initialize the function with the very string that he was looking to get back. I.e., your example requires that he has the value in string format in the first place, and if that were the case, then he'd already have what he was looking for and he wouldn't need gmp. (Granted, it's not clear where the initial value is coming from, so... who knows... :) – Alex Howansky Nov 05 '11 at 16:11
Well, the source must be a string. Isn't all PHP input string? – hakre Nov 05 '11 at 16:18

Madara's Ghost · Answer 2 · 2011-08-22T17:44:50.347

4

Use strval().

echo strval($bigint); // Will output "99999999999999999"

EDIT: After a slightly better research (> 5000ms), I see that it is impossible to echo numbers to that precision, because PHP cannot save an integer of that size (depends on OS bit system, 32/64). Seems like it's not possible to do it without losing precision.

edited Aug 22 '11 at 17:44

answered Aug 22 '11 at 17:36

Madara's Ghost

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@Evan ;) 5 seconds worth of Google search. – Madara's Ghost Aug 22 '11 at 17:38
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sorry, that is just the same as casting it as a string by (string) and it does not work. It will just output 1.0E+19 – buggedcom Aug 22 '11 at 17:38
Actually, it calls `_toString()`, which isn't the same. But `strval` should have worked. – Evan Mulawski Aug 22 '11 at 17:42
@Evan - what version of PHP are you using for that to work? Have you tested it yourself? – buggedcom Aug 22 '11 at 17:45
@Rikudo, thanks. I guess I didn't really understand what "losing precision" was before. – buggedcom Aug 22 '11 at 17:49
@buggedcom: It will not work on 64-bit systems. Because of integer overflow, it is not universally possible. – Evan Mulawski Aug 22 '11 at 17:50
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You can use third-party libraries, though. See http://stackoverflow.com/questions/211345/working-with-large-numbers-in-php – Evan Mulawski Aug 22 '11 at 17:51
@mario: Correct. I missed the "not." – Evan Mulawski Aug 22 '11 at 17:54

score 0 · Answer 3 · answered May 24 '13 at 04:50

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Just store the value as string and display...!

   $bigint = '9999999999999999999';

    var_dump($bigint);

Output:

string(19) "9999999999999999999"

answered May 24 '13 at 04:50

ShivarajRH

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score 0 · Answer 4 · answered Aug 22 '11 at 17:38

0

Use printf(), it's made for that:

echo printf("%d", $bigint);

answered Aug 22 '11 at 17:38

Arnaud Le Blanc

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This doesn't work for values greater than 32 bit. (Or 64, in whichever case.) – Alex Howansky Aug 22 '11 at 17:42

PHP: How to convert bigint from int to string?

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