检查字符串是否包含数字，同时允许多个小数点？

This is to test version numbers. They need to contain only numbers, but can have multiple decimal points.

For example:

$a = '1.2.3';

is_numeric($a) returns false, and floatval($a) strips out the extra decimal sections, without returning a useful answer to the test.

Is there any PHP function that would do this?

You can use preg_match():

if(preg_match('~^([0-9]+(\.[0-9]+)*)$~', $string)) {
    echo 'ok';
}

The regex pattern matches from the begin ^ to the end $ of the string and checks if it begins with a number and then contains only numbers - optionally separated by single dots - and ends with a number again.

You can use the strcspn function:

$q='1.2.3';

if (strcspn($q, '0123456789') != strlen($q))
  echo "true";
else
  echo "false";