C/C++ header and implementation files: How do they work?

by

The header file declares functions/classes – i.e. tells the compiler when it is compiling a .cpp file what functions/classes are available.

The .cpp file defines those functions – i.e. the compiler compiles the code and therefore produces the actual machine code to perform those actions that are declared in the corresponding .hpp file.

In your example, main.cpp includes a .hpp file. The preprocessor replaces the #include with the contents of the .hpp file. This file tells the compiler that the function myfunction is defined elsewhere and it takes one parameter (an int) and returns an int.

So when you compile main.cpp into object file (.o extension) it makes a note in that file that it requires the function myfunction. When you compile myfunction.cpp into an object file, the object file has a note in it that it has the definition for myfunction.

Then when you come to linking the two object files together into an executable, the linker ties the ends up – i.e. main.o uses myfunction as defined in myfunction.o.

I hope that helps

More Related Contents:

  1. Pros & Cons of putting all code in Header files in C++?
  2. String return from member function in C++
  3. how to write makefile when two header files include eachother in c++? [duplicate]
  4. Compilation error: expected constructor, destructor, or type conversion before ‘;’ token [closed]
  5. Error when building a C++ program for the second time [closed]
  6. What is the difference between #include and #include “filename”?
  7. Why aren’t my include guards preventing recursive inclusion and multiple symbol definitions?
  8. Using G++ to compile multiple .cpp and .h files
  9. What should go into an .h file?
  10. How to enable C++17 compiling in Visual Studio?
  11. Why does C++ compilation take so long?
  12. multiple definition in header file
  13. The benefits / disadvantages of unity builds? [duplicate]
  14. How to compile Qt 5 under Windows or Linux, 32 or 64 bit, static or dynamic on Visual Studio or g++
  15. Parsing strings of user input using the cparse library from git
  16. Elegantly call C++ from C
  17. Difference between and ?
  18. Undefined reference error for template method [duplicate]
  19. How to create a shared library with cmake?
  20. Profiling the C++ compilation process
  21. Is #pragma once part of the C++11 standard?
  22. scope of using declaration within a namespace
  23. Handling header files dependencies with cmake
  24. How to make Visual Studio use the native amd64 toolchain
  25. Header file included only once in entire program?
  26. What’s the differences between .dll , .lib, .h files?
  27. Can I use Qt without qmake or Qt Creator?
  28. How to prevent non-specialized template instantiation?
  29. if / else at compile time in C++?
  30. C++ Circular Dependency in Header Files

Leave a Comment