php-little pitfalls of weak typing

An issue discussed in the group today, record it.

The origin of the problem is
var_dump(md5('240610708') == md5('QNKCDZO')); //true
Two md5 strings, compared with the comparison operator (==), they are actually equal of.
Output the following two values:
md5('240610708') //0e462097431906509019562988736854
md5('QNKCDZO') //0e8304004519934940580242199033 91
When I saw the result, I felt that it was intval at first glance, so 0 == 0 returned true.
After being reminded later, I found out that this was not the case.
php comparison operator:
http://php.net/manual/zh/language.operators.comparison.php
Example:

如果比较一个数字和字符串或者比较涉及到数字内容的字符串，则字符串会被转换为数值并且比较按照数值来进行。此规则也适用于 switch 语句。当用 === 或 !== 进行比较时则不进行类型转换，因为此时类型和数值都要比对。

<?php
var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
var_dump("10" == "1e1"); // 10 == 10 -> true
var_dump(100 == "1e2"); // 100 == 100 -> true

switch ("a") {
case 0:
    echo "0";
    break;
case "a": // never reached because "a" is already matched with 0
    echo "a";
    break;
}
?>

In other words, this equality is not because the two strings are intval, and become 0=0
but is numericized 0e4xxx == 0e8xxx, which is scientific notation, 0*10 to the nth power, that is, 0.0000 and 0.00000000
, so there will be equal results.

The above has introduced the small pitfalls of php-weak typing, including aspects of it. I hope it will be helpful to friends who are interested in PHP tutorials.