undefined reference to f_gets

This error message typically occurs when the linker is unable to find the definition for a function named f_gets. This usually happens when the function is declared in a header file, but not defined in any source file that is being linked.

To resolve this error, you need to make sure that the function f_gets is defined in one of your source files, or in a library that is being linked. You may also need to check that you have included the correct header file that declares the function.

If you are using a library that provides the f_gets function, you may need to link your program with that library. You can do this by adding the library to your linker command, or by adding it to your project settings if you are using an integrated development environment (IDE).

Overall, the solution to this error depends on the specific context in which it is occurring, and may require some investigation to determine the root cause