C++ Primer, Fifth Edition

2.6.3. Writing Our Own Header Files

Although as we’ll see in § 19.7 (p. 852), we can define a class inside a function, such classes have limited functionality. As a result, classes ordinarily are not defined inside functions. When we define a class outside of a function, there may be only one definition of that class in any given source file. In addition, if we use a class in several different files, the class’ definition must be the same in each file.

In order to ensure that the class definition is the same in each file, classes are usually defined in header files. Typically, classes are stored in headers whose name derives from the name of ...