Check whether the string is a unix timestamp

Question

I have a string and I need to find out whether it is a unix timestamp or not, how can I do that effectively?

I found this thread via Google, but it doesn't come up with a very solid answer, I'm afraid. (And yes, I cribbed the question from the original poster on the aforementioned thread).

Answer 1

As a unix timestamp is a integer, use is_int(). However as is_int() doesn't work on strings, we check if it is numeric and its intergal form is the same as its orignal form. Example:

( is_numeric($stamp) && (int)$stamp == $stamp )

Answer 2

You want to check if a string contains a high number?

is_numeric() is the key

Or convert it to DateTime and do some checks with it like an expected date range.

Answer 3

Ok, after fiddling with this for some time, I withdraw the solution with date('U') and suggest to use this one instead:

function isValidTimeStamp($timestamp)
{
    return ((string) (int) $timestamp === $timestamp) 
        && ($timestamp <= PHP_INT_MAX)
        && ($timestamp >= ~PHP_INT_MAX);
}

This check will only return true if the given $timestamp is a string and consists solely of digits and an optional minus character. The number also has to be within the bit range of an integer (EDIT: actually unneeded as shown here).

var_dump( isValidTimeStamp(1)             ); // false
var_dump( isValidTimeStamp('1')           ); // TRUE
var_dump( isValidTimeStamp('1.0')         ); // false
var_dump( isValidTimeStamp('1.1')         ); // false
var_dump( isValidTimeStamp('0xFF')        ); // false
var_dump( isValidTimeStamp('0123')        ); // false
var_dump( isValidTimeStamp('01090')       ); // false
var_dump( isValidTimeStamp('-1000000')    ); // TRUE
var_dump( isValidTimeStamp('+1000000')    ); // false
var_dump( isValidTimeStamp('2147483648')  ); // false
var_dump( isValidTimeStamp('-2147483649') ); // false

The check for PHP_INT_MAX is to ensure that your string can be used correctly by date and the likes, e.g. it ensures this doesn't happen*:

echo date('Y-m-d', '2147483648');  // 1901-12-13
echo date('Y-m-d', '-2147483649'); // 2038-01-19

---

^{(*) Note: I'm not 100% sure, the bit range corresponds with what date can use though}

Answer 4

This doesn't account for negative times(before 1970), nor does it account for extended ranges(you can use 64 bit integers so that a timestamp can represent a value far after 2038)

$valid = ctype_digit($str) && $str <= 2147483647;