Why md5('240610708') is equal to md5('QNKCDZO')? [duplicate]

Question

This question already has answers here:

Why does PHP convert a string with the letter E into a number? (7 answers)

Closed 8 years ago.

var_dump(md5('240610708') == md5('QNKCDZO'));

Output:

bool(true)

Example: http://3v4l.org/2vrMi

Answer 1

md5('240610708') 's result is 0e462097431906509019562988736854.

md5('QNKCDZO') 's result is 0e830400451993494058024219903391.

They are both float number format strings (numerical strings), and if you use == in php, when compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically.

Both of the strings are converted to 0 when compared with ==, if you want to compare them as string, remember to use ===(strict comparison) instead.

See: PHP expresses two different strings to be the same

Answer 2

You need to use the type-sensitive comparison operator ===.

The hashes evaluate to 0e462097431906509019562988736854 and 0e830400451993494058024219903391, respectively. When you use ==, each is converted to a numeric representation because of the e (scientific notation), so they each become 0. 0 == 0 is true.

On the other hand, this:

md5('240610708') === md5('QNKCDZO')

returns false because the string values are different. === forces type-sensitive comparison.