Bug #75568 [Opn->Nab]: a strange behavior of float and string comparison

Edit report at https://bugs.php.net/bug.php?id=75568&edit=1 ID: 75568 Updated by: nikic@php.net Reported by: 605231181 at qq dot com Summary: a strange behavior of float and string comparison -Status: Open +Status: Not a bug Type: Bug Package: *General Issues Operating System: not related PHP Version: 7.1.12 Block user comment: N Private report: N New Comment: Floating point values have a limited precision. Hence a value might not have the same string representation after any processing. That also includes writing a floating point value in your script and directly printing it without any mathematical operations. If you would like to know more about "floats" and what IEEE 754 is, read this: http://www.floating-point-gui.de/ Thank you for your interest in PHP. Previous Comments: ------------------------------------------------------------------------ [2017-11-24 16:10:10] 605231181 at qq dot com Description: ------------ I've recently noticed a strange behavior of php comparison on float/double and string, i searched online but found nothing related, I'm not sure if it's a real bug or not, so I've posted it here. I understand there might be some type conversion problem, but i don't quite understand what's really going on. I understand the problem is about float number, but I'm not using === to compare, and the output(var_dump) of two value is same, so I expect same results here. As a note, not every case result wrong, some case is working. Test script: --------------- code is running in Psy Shell v0.8.2, but the issue can be reproduced anywhere. >>> $a=986365.1;$b='986365.1';var_dump($a,$b,$a==$b); float(986365.1) string(8) "986365.1" bool(true) >>> $a='73.01'*13510;$b='986365.1';var_dump($a,$b,$a==$b); float(986365.1) string(8) "986365.1" bool(false) >>> $a='5.01'*10.1;$b='50.601';var_dump($a,$b,$a==$b); float(50.601) string(6) "50.601" bool(true) Expected result: ---------------- i expect same result bool(true) in all test scripts. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=75568&edit=1