How to permanently store information using C program?

Question

I am trying to get input from the user that the program will remember every time it runs. I want to do this in C. Based on my limited knowledge of computers, this will be stored in the storage/hard drive/ssd instead of the RAM/memory. I know I could use a database, or write to a text file, but I don't want to use an external file or a database, since I think that a database is a bit overkill for this and an external file can be messed with by the user. How can I do this (get the user to enter the input once and for the program to remember it forever)? Thanks, (If anyone needs me to clarify my question, I'd be happy to do so and when I get an answer. I will clarify this question for future users.)

Answer 1

People have done this all kinds of ways. In order from best to worst (in my opinion):

1. Use a registry or equivalent. That's what it's there for.
2. Use an environment variable . IMO this is error prone and may not really be what you want.
3. Store a file on your user's computer. Easy to do and simple.
4. Store a file on a server and read/write to the server via the network. Annoying that you have to use the network, but OK.
5. Modify your own binary on disk. This is fun as a learning experience, but generally inadvisable in production code. Still it can be done sometimes especially using an installer.
6. Spawn a background process that "never" dies. This is strictly worse than using a file.

Answer 2

You won't be able to prevent the user from modifying a file if they really want to. What you could do is create a file with a name or extension that makes it obvious that it should not be modified, or make it hidden to the user.

Answer 3

There isn't really any common way that you could write to a file and at the same time prevent the user from accessing it. You would need OS/platform level support to have some kind of protected storage.

The only real alternative commonly available is to store the information online on a server that you control and fetch it from there over the network. You could cache a cryptographically signed local copy with an expiration date to avoid having to connect every time the program is run. Of course if you are doing this as some kind of DRM or similar measure (eg, time-limited demo), you will also need to protect your software from modification.

(Note that modifying the program itself, which you mentioned in a comment, is not really any different from modifying other files. In particular, the user can restore an earlier version of the program from backup or by re-downloading it, which is something even a casual user might try. Also, any signature on the software would become invalid by your modifications, and antivirus software may be triggered.)

If you simply wish to hide your file somewhere to protect against casual users (only), give it an obscure name and set the file hidden using both filesystem attributes and naming (in *nix systems with a . as the first character of file name). (How hidden you can make it may be thwarted by permissions and/or sandboxing, depending on the OS.)

Also note that if your goal is to hide the information from the user, you should encrypt it somehow. This includes any pieces of the data that are part of the program that writes it.

edit : In case I guessed incorrectly and the reason for wanting to do this is simply to keep things "clean", then just store it in the platform's usual "user settings" area. For example, AppData or registry on Windows, user defaults or ~/Library/Application Support on macOS, a "dotfile" on generic *nix systems, etc. Do not modify the application itself for this reason.

Answer 4

If you want to persist data, the typical way to that is to store it to a file. Just use FILE* and go about your business.

Using a database for this may be an overkill, it depends on how you want to later access the data once it is stored.

If you just load the data from the file and search through it, then there is no need for a database, if you have loads of data and want to make complex searches, then a database is the way to go. If you need redundancy, user handling, security then choose a database, since the developers of each one already spent a lot of time fixing this.