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Can header files have implementation?
It is perfectly valid to have an implementation of a function in a header file. The only issue with this is breaking the one-definition-rule. That is, if you include the header from multiple other files, you will get a compiler error.
Where are header files used?
The primary purpose of a header file is to propagate declarations to code files. Header files allow us to put declarations in one location and then import them wherever we need them. This can save a lot of typing in multi-file programs.
Can header files contain code?
Code in headers is generally a bad idea since it forces recompilation of all files that includes the header when you change the actual code rather than the declarations. It will also slow down compilation since you’ll need to parse the code in every file that includes the header.
What is the name of the header file?
A file that contains a class declaration is called header file. The name of the class is usually the same as the name of the class, with a .h extension. For example, the Time class would be declared in the file Time .h.
How can a C + + header file include implementation?
It is possible to write code that does not rely on header files, and it is possible to write code that is made up of just header files (the STL and Boost libraries are good examples of that).
Do you have to include a header file in a translation unit?
If a header file is included multiple times in a translation unit (TU), it should not break builds. If you need the facilities declared in a header file, you should not have to include any other headers explicitly. You should not be able to remove any information from a header without causing builds to fail.
Do you include the extension or the header?
The longer answer is that you may be able to include either, and it might work for you, but both will give slightly different results. What “include” does is basically copy/paste the file in at that line. It doesn’t matter what the extension is, it will include the contents of the file the same way.