I'd like to do this in baby steps, but the end goal is to build a cross platform, graphical user interface that basically takes a file and loads the data into an array that is uploaded on the Arduino Mega. (Right now, I've made a simple C++ script that I run through a command prompt. It reads the .txt file and then builds the Arduino sketch based on the data it finds in the .txt file. Then, I have to copy the text into the Arduino software and upload that to the board. I want to streamline and idiot proof this process so that the end user can simply double click an icon, load a .txt file, choose a couple of parameters and then click "upload" and the program will build the code and upload it to the Arduino)
Well that seems like a big ask if you have little experience.
One way might be with an arduino IDE going you would put your program (whatever you are doing with the text) in a sketch and develop it to read your text file into an array you have set up for the purpose and then when it compiles transfer it to the chip
The answers can only be general without a more detailed idea of what you want to do with the text file in the long run?