I've been working on a project in C++ using openGL and am looking to save the current scene to a text file. Something simple along the lines of, cube at x,y,z and its color etc. 

My question is about how to make sure that the file has not been changed by a user. I thought about calculating a checksum of the string and including that in the file.

e.g. checksum, string

But again this is open to the user modifying the values.

Any recommendations or is this just a case of writing a good parser?

Cheers