I was looking at some form validation code someone else had written and I saw this:
strlen() == 0
When testing to see if a form variable is empty I use the empty() function. Is one way better than the other? Are they functionally equivalent?
strlen is to get the number of characters in a string while empty is used to test if a variable is empty
Meaning of empty:
empty("") //is empty for string
empty(0) // is empty for numeric types
empty(null) //is empty
empty(false) //is empty for boolean
There are a couple cases where they will have different behaviour:
empty('0'); // returns true,
strlen('0'); // returns 1.
empty(array()); // returns true,
strlen(array()); // returns null with a Warning in PHP>=5.3 OR 5 with a Notice in PHP<5.3.
empty(0); // returns true,
strlen(0); // returns 1.
The following things are considered to be empty:
"" (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)
var $var; (a variable declared, but without a value in a class)
strlen() simply check if the the string len is 0. It does not check for int, float etc. What is your situation.
$f = 0; echo empty($f)? 'Empty':'Full'; // empty
$f = 0; echo strlen($f); // 1
For forms I use isset. It's more explicit. ;-)
empty() will return true if $x = "0". So there is a difference.
empty is the opposite of boolean false.
empty is a language construct.
strlen is a function.
strlen returns the length of bytes of a string.
strlen($str)==0 is a comparison of the byte-length being 0 (loose comparison).
That comparison will result to true in case the string is empty - as would the expression of empty($str) do in case of an empty (zero-length) string, too.
However for everything else:
empty is the opposite of boolean false.
strlen returns the length of bytes of a string.
They don't share much with each other.
empty() is for all variables types. strlen(), I think, is better to use with strings or something that can be safely casted to strings. For examle,
strlen(array());
will throw PHP Warning: strlen() expects parameter 1 to be string, array given error
when the input is 0,
strlen(0) = 1
empty(0) = false <-- non-empty
来源：https://stackoverflow.com/questions/7072948/is-there-a-difference-between-strlen-0-and-empty