What Are Illegal Characters?

Illegal characters do not mean that a character is illegal, but that a character cannot appear in a defined rule.

Illegal characters do not mean that a character is illegal, but that a character cannot appear in a defined rule.

1. For example, in the file (folder) name of the operating system, it has its own set of rules: \ / *?: | Therefore, the characters \ / *?: "<> | Are illegal characters in this rule.

2. For example, in a programming language such as a C # variable, a name that does not begin with a number can appear. A variable name like 0tmp is illegal.

3. For example, in the Java language, variable names can only be numbers, letters, underscores, and $, which cannot start with a number.

In web programming, since the server will accept requests from clients, the programmer must ensure the legitimacy of the character data from the request, such as the T-SQL keywords "select, update, delete, which are sensitive to database operations , insert, table, while 1 == 1, name like '*', etc. are illegal request characters.

Some special characters in ASP can only be used by web page code writers. If others also use it, they can constitute attack code, such as SQL injection attacks, so sometimes they need to be blocked, such as select delete, update, insert , '= Etc.