如果声明不起作用，但是有点起作用

Question

I made a php script to see if what the contents of a txt file are the same as the users input. I wrote an if statement to see if it is correct and if it isn't send it to an else. If i dont send any variables, then it works, and displays

a is b is file is 1

but if i enter the file and the correct contents it displays

a is test.txt b is hello file is hello 0

Here is my code

<?php
session_destroy();
$a=htmlspecialchars($_REQUEST['a']);
$b=htmlspecialchars($_REQUEST['b']);
$my_file = file_get_contents($a);
echo "a is $a\n";
echo "b is $b\n";
echo "file is $my_file\n";
if ( $my_file == $b ) {
echo "1";
}else {
echo "0";
}
?>

Any ideas?

Answer 1

These are un-initialized variables, so if you enter nothing, then you're getting if (false == false) which is true.

This is because php interprets null as being false. It's weird, I acknowledge.

Either check to see if your variables have been set, or initialize them with defaults.

Answer 2

为了安全起见，请尝试在从文件读取的内容中使用htmlspecialchars函数，然后在从文件读取的输入和用户输入中也使用trim