PHP functia intval functioneaza ciudat


(Dániel Bokor) #1

Se da urmatorul cod:

$val = 8.12;
var_dump (intval($val*100)); exit;

valoarea returnata este int(811) in loc de int(812); in schimb

var_dump (intval(812)); exit

afiseaza corect int(812)

Are cineva vreo explicatie? o.0

LE. Comportamentul este corect in cazul in care $val = 8.11;


(Dániel Bokor) #2

Explicatii aici http://php.net/manual/en/function.intval.php#112039


(Victor Stanciu) #3

Problema nu e la intval, ci la inmultire. Explicatia pe larg, direct din manual, floating point numbers:

[…] rational numbers that are exactly representable as floating point numbers in base 10, like 0.1 or 0.7, do not have an exact representation as floating point numbers in base 2, which is used internally, no matter the size of the mantissa. Hence, they cannot be converted into their internal binary counterparts without a small loss of precision. This can lead to confusing results: for example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8, since the internal representation will be something like 7.9999999999999991118

So never trust floating number results to the last digit, and do not compare floating point numbers directly for equality.

Ca o paranteza, nu folositi niciodata operatorii aritmetici atunci cand lucrati cu valori numerice importante, gen bani. Folositi extensia BC Math. E cam peste mana sa scrii bcmul($val, 100) in loc de $val * 100, dar asta e situatia.


(adrian) #4

Cand te lovesti de problema asta e un soi de prag “Ok, scriu PHP de ceva vreme…”, un soi de level up.


(Viorel Sfetea) #5

“Problema” e prezenta si in alte limbaje, cum ar fi Python: Floating Point Arithmetic: Issues and Limitations

Cu singura diferenta ca in Python ai mai putine sanse sa te lovesti de ea. Bine, asta pana vrei sa lucrezi cu JSON: http://stackoverflow.com/questions/1447287/format-floats-with-standard-json-module (PS: al doilea raspuns e bun aici, nu primul care e un hack destul de tricky, caruia trebuie sa ii faci revert dupa ce l-ai folosit)


(Dániel Bokor) #6

Exact asa m-am simtit :slight_smile: