php operator == (sort of equality) and the integer 0

Question

php, my dearest old frienemy.

ok, so i can come to terms with why the string '0' would be a falsie value. that's only fair seeing as how '0' is the same as 0 in a loosely typed language, and 0 is false in a loosely typed language. so this gives that false == 0 == '0'.

fine fine... BUT!! what is this all about?

<?php
    print "number of surprised persons: " . ('false' == 0);

the output is....

number of surprised persons: 1

how is this reasonable? am i the only one who's surprised by this? what am i failing to see?

further testing has proven that the integer 0 is equal (by operator ==) to

0        <-- integer
false    <-- boolean
null     <-- just.. you know, null
'0'      <-- string
''       <-- string
'false'  <-- string
'true'   <-- string
'null'   <-- string

naturally, i mostly use operator === to compare stuff. and now that i know about this, i'll have to adjust my programming of course, no question about that. but still! can someone shed some light pl0x?

Answer 1

It's because, when you compare a string to an integer, they don't both get converted to strings, or to booleans - they get converted to integers. For PHP, when you think about it, this isn't strange at all (comparatively, I suppose).

'true' == 0
// is the same as
(int)'true' == 0
// is the same as
0 == 0
// is the same as
true

And this is true for any non-numeric string as well as the string "0". The reason 1 is printed out is because the string version of true is 1 (and the string version of false is an empty string).

Answer 2

As far as you're concerned about the output:

('false' == 0) = boolean TRUE = string "1".

echo is triggering string context.

But from your comment below I've just seen, that you'd like to learn more about the comparison. Take a look what you do:

Example     Name     Result
$a == $b    Equal    TRUE if $a is equal to $b after type juggling.

so you are doing a non-strict comparison of a number with a string:

If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically. (REF)

Note: Number, not integer as written in the accepted answer:

<?php
print "number of surprised persons: " . ('false' == 0.3 - 0.2 - 0.1);

Have fun.