为什么chr（0x00）在PHP中被认为是真的？

Question

0x00 is known to be the null character.

Then why in PHP (bool) null returns false, but (bool) chr(0x00) returns true ?

In the other hand, (bool)intval(chr(0x00)) returns false.

The above is valid for all PHP versions between 5.4 and 7.0.0 beta2, so there must be a reason.

Edit: I'm asking this question, because I have a bit(1) column in MySQL, and chars 0x00 or 0x01 are returned.

if ($test['bit1column']) will always pass, because both chars are considered as true, so I'm forced to do an if ($test['bit1column'] === chr(0x01)) .

This is correct at least for PHP 5.6 with MySQL 5.5.44. Why? I can't see any logic here.

Answer 1

Then why in PHP (bool) null returns false, but (bool) chr(0x00) returns true ?

it's because chr(0x00) gives you a one char long string:

$ php -r "var_dump(chr(0x00));"

string(1) ""

and then ( as per documentation ) the only case string can give false when casted to boolean is either the empty one (so length is 0) or the string holding "0" as its content:

When converting to boolean, the following values are considered FALSE:

the empty string, and the string "0"

This is neither the case here as our string is not holding 0 nor is empty as it holds 1 character. So it cannot be false and therefore is true .

EDIT

I assume you expected C / C++ like behaviour where strings are 0x00 terminated. This is not the case in PHP.

Answer 2

In PHP the following things are false :

• "" (an empty string)
• 0 (0 as an integer)
• 0.0 (0 as a float)
• "0" (0 as a string)
• null
• false
• array() (an empty array)

Everything else is true . chr(0x00) results in a string with a single character (the NUL byte). That's not an empty string and not a string with the character 0 , so it does not qualify as false .

Trying to cast the string "\\0" ( NUL byte) to an int results in 0 , because there's no parseable integer in the string, so the result is 0 . 0 is false .