来自is_numeric / foreach例程的意外输出

Question

Ref: http://php.net/manual/en/function.is-numeric.php.

Example #1 is_numeric().

Why does the Example #1 routine output 1337 4 times instead of 1 time? My expectation is the routine would ouput the other 3 numeric values that follow 1337. Even if I re-arrange the order of the elements it still outputs 1337 4 times. I understand hex and binary values are not allowed, but why does the routine output 1337 for those values. Also, if I change 1337 to 01337 the ouput is 735.

Why these confusing outputs?

<?php
$tests = array(
    "42", 1337, 0x539, 02471, 0b10100111001, 1238.443e2, "not numeric",
    array(), 9.1, null
);

foreach ($tests as $element) {
    if (is_numeric($element)) {
        echo var_export($element, true) . " is numeric", PHP_EOL;
    } else {
        echo var_export($element, true) . " is NOT numeric", PHP_EOL;
    }
}
?>

Output:
'42' is numeric
1337 is numeric
1337 is numeric
1337 is numeric
1337 is numeric
123844.300000000002910383045673370361328125 is numeric
'not numeric' is NOT numeric
array () is NOT numeric
9.0999999999999996447286321199499070644378662109375 is numeric    
NULL is NOT numeric

Answer 1

Base-N notation syntax

which you had to know to pull this off

Hexadecimal

A number prefixed with 0x will be interpreted as base-16

Octtal

A number prefixed with 0 will be interpreted as base-8

Binary

A number prefixed with 0b will be interpreted as base-2

Conversion to Decimal

• 1337 base10 (base10 value: 1337)
• 0x539 base16 (base10 value: 1337)
• 02471 base8 (base10 value: 1337)
• 0b10100111001 base2 (base10 value: 1337)

Numbers in strings are always shown in base-10

Converting these numbers to a string, as with var_export, will convert them to base-10, unless you use number_format.