Undefined symbol key4_status (referred from data.o).

This error message typically indicates that the linker is unable to find the definition of the symbol "key4_status" in the code. This can happen if the symbol is not declared or defined in any of the source files or libraries that are being linked.

To resolve this issue, you need to ensure that the symbol is declared and defined properly in your code. If the symbol is defined in another source file, you need to make sure that it is included in the build process and linked with your code.

Alternatively, if the symbol is defined in a library, you may need to add the library to the linker command line or to your build system configuration.

Make sure that you have included all the necessary header files and libraries, and that they are in the correct location. Check for any typos or spelling errors in the symbol name, and make sure that the symbol is not defined multiple times in different source files.

If you are still unable to resolve the issue, you may need to seek assistance from a more experienced developer or reach out to the support team of the development environment you are using.