No amount of header file inclusion is going to solve this issue, header files are included by the pre-processor ( before compilation and linking). In this lecture you will acquire a knowledge on downloading and installing MPLAB X IDE and XC8 Compiler to your PC,This is a course on programming in MPLAB X.
So it is likely that you have simply omitted to add the C sources to your project. Bookmark File PDF Mplab C18 C Compiler Libraries Microchip Technology difference between baudrate and kHz MicrochipInstalling MPLAB XC8 C Compiler - Developer HelpAll Forums Microchip In most IDEs (and I don't believe MPLAB X is any different), you add the C source files to a " project", and the IDE's project manager will manage the separate compilation and linking for you. It is the linker that is issuing the undefined symbols diagnostic, almost certainly because you have not separately compiled the C files and passed the generated object code to the linker. The object files generated by separate compilation are then passed to the linker which resolves the external references in one object file with definitions provided in other object files (or static libraries included in the link). The previous version MPLAB XC8 C compiler was The MPLAB XC8 compiler can be activated in several different operating modes: Free, Standard and PRO. The issue might have been caused by using the MPLab X Build Configurations feature and adding the C file to a certain build configuration. The purpose of the headers in this process is to make visible to the compiler the symbols that will be defined in separate object files. Removing my file from the MPLab X Project Configuration and adding it back in resolved the issue. That is to say, each C file must be separately compiled to create an object file.
The most likely cause being that you have not actually linked the object code for each C file that the compiler compiled.
You get undefined symbols when the linker cannot match the symbols referenced in the code it has been asked to link. Header files do not link C files - they simply declare symbols.