I know this is probably a primitive topic for most, but I just got into coding in c++ because a simple project I am working on that uses esp8266 which can be programmed using c++. Before this I only had experiemce with python, javascript and typescript.
Now to my problem: I am trying to split my code that is getting longer into multiple files.
I already think that I understand right that each library has a header (.h) file and source (.cpp or .c in case of c) file. The first thing I already have problem with is that as you are defining your functions and classes in the header file and then implementing them in the source file you are repeating yourself with the declarations which is not something I would like. I presume that most IDEs will probably automatically help you with generating or editing the header file automatically as you change code in the source file and I guess I will need to learn to live with it.
Then there’s the thing with importing. It may happen that if you create a library it also has some dependencies that it needs to include. But as far as I understand one library shouldn’t be included multiple times. So from what I can see most libraries check whether a global variable with an ARBITRARY name that the library chooses itself is not defined and then if that’s true it defines that variable to indicate it has been included (the name of the variable is not compketely arbitrary and usually follows LIBRARY_NAME_H but the convention cannot be really relyed on). When the library includes other library it also needs to check whether the variable of that library that is defined on its import is defined. The main file should also probably check this for every library it includes because it can’t know what lins were already imported by libs it imported? Am I getting something wrong or is it sometimes ok for some libraries to be included multiple times. There’s the to handle these situations?
You can generally rely on a header file doing its own check to prevent being included twice. If a header doesn’t do that, it’s either wrong or doing something fucky. It is merely a convention, but it’s so widespread that you really don’t need to worry about it.
You are mixing up some terms, so I want to help clarify. When you #include a header file, you aren’t importing a library. You are telling the compiler to insert the contents of that header file into your source where the #include line is. A library is something different. It is an already-compiled binary file. A library should also come with a header file to tell you what functions and classes are present in the library, but that header isn’t itself the library.
It may seem annoying to have to repeat yourself between headers and source, but it’s honestly something you get used to.
Thank you for your explanation! From what I have read ‘#pragma once’ solves the problem with mutiple includes for most modern compilers, but it’s always better to write the import guards for better compatability?
There’s no downside to writing the guards afaik, but I’m more of a c programmer. It’s been a while since I did much c++, so I’m not up on modern conventions. But dealing with legacy code adhering to older conventions often comes with the territory with c and c++, so it’s something to keep in mind.
You probably don’t have to worry about the compatability of
#pragma onceso just use that. The only reasons to not use it is if it’s important to only use standard compliant c for whatever reason or if you need to support some arcane compiler that doesn’t support#pragma once. Realistically, neither of these are situations that you’ll ever be put in and if you are you probably have much larger things that you need to worry about.