为什么我们应该在登录中使用mysqli_real_escape_string（）和stripslashes（）函数并注册php文件

Question

1- Why we should use the mysqli_real_escape_string() and the stripslashes() functions in a register and login php files?

2- Does these functions change the contents of the fields? If the answer is yes as the result the contents of the fields such as the username will change and the next time if the user want to login with his/her username It can not, because the contents of the username has been changed already, for example at the time of the registering in a website and now and as the result it can not login to the website because the contents of the fields such as the username has been changed by the the mysqli_real_escape_string() and the stripslashes() functions.

I have two ambiguity in the above questions.

Answer 1

Using these functions makes your site less vulnerable to SQL injection attacks, where an attacker puts SQL syntax into a form field to compromise your site. mysqli_real_escape_string() "escapes" special characters so that MySQL interprets them as literal string characters rather than operators in the query.

These functions only affect characters that are important to SQL commands, and will not affect legitimate input, while foiling nefarious users.