What are the advantages and disadvantages of implementing classes in header files?

Question

I love the concept of DRY (don\'t repeat yourself [oops]), yet C++\'s concept of header files goes against this rule of programming. Is there any drawback to defining a clas

Answer 1

The main reason not to implement a class in the header file is: do the consumers of your class need to know its implementation details? The answer is almost always no. They just want to know what interface they can use to interact with the class. Having the class implementation visible in the header makes it much more difficult to understand what this interface is.

Beyond considerations of compactness and separating interface from implementation, there are also commercial motivations. If you develop a library to sell, you (probably) do not want to give away the implementation details of the library you are selling.