如何将字符串转换为整数，但将“foo”与“0”区分开来？

I need to convert strings to intiger but with distinguish "foo" from "0", because intval() php function converts non numeric values to 0.

With inputs:

$a = "10"
$b = "foo"
$c = "0"
$d = "10.5"

I expecting after convertion:

$a == 10
$b == "foo" // or false or whatever that is not an integer
$c == 0
$d == 10.5

You could consider using conditional operator, code would like somehow as below:

$foo = is_numeric($bar) ? (float) $bar : $bar;

There's no reason to overthink that solution, this should be enough.

You could always use is_numeric().

if (is_numeric($value)) {
    $integer = (int) $value; // Or use intval()
    $floatOrInteger = $value + 0; // Can also give a float, so watch it.
} else {
    echo "Value is not numeric!";
}

See the code in action here: https://3v4l.org/j4Utb

EDIT

Look at the comments of the documentation I linked if you want more fine-grained control. There's tons of really useful tricks there.

You could use is_int to test, if it is really an integer. After that, you have to determine, if it's a float. A simple check like (int) $value == (float) $value could be sufficient in your case.

Wrapping things up in a function could look like this:

function toNumber($value) {
    if (is_numeric($value)) {
        if ((int)$value != (float)$value) {
            return (float) $value;
        }
        return (int) $value;
    }
    return $value;
}

The result of your examples (and some others) would be

var_dump(toNumber('10')) . "
";
var_dump(toNumber('foo')) . "
";
var_dump(toNumber('0')) . "
";
var_dump(toNumber(10.5)) . "
";
var_dump(toNumber('-10')) . "
";
var_dump(toNumber('')) . "
";
var_dump(toNumber('10.0')) . "
";

with

int(10)
string(3) "foo"
int(0)
float(10.5)
int(-10)
string(0) ""
int(10)