How does the class library read the configuration file (App. config )?

We know that in winform or console applicationProgram, We can use the app. config file to store the configuration information of the program. Then we use the system. configuration class for calling, reading, or updating. . Config file. Then we will automatically call this configuration file when using this program.
However, I encountered the following problem: when I use the app in the class library. the class library name Is ts. utilities. after the DLL and IDE are compiled, the app is automatically added. the config file is compiled into ts. utilities. DLL. config file, but when other programs or Class Libraries call it, it fails because the configuration file cannot be found. The error message is: object reference not set to an instance of an object.
Let's take a look at it. Why?