Header-only libraries and multiple definition errors

c++ header multiple-definition-error
Epro picture Epro · Oct 20, 2010 · Viewed 7.2k times · Source

I want to write a library that to use, you only need to include one header file. However, if you have multiple source files and include the header in both, you'll get multiple definition errors, because the library is both declared and defined in the header. I have seen header-only libraries, in Boost I think. How did they do that?

Answer

John Dibling picture John Dibling · Oct 20, 2010

Declare your functions inline, and put them in a namespace so you don't collide:

namespace fancy_schmancy
{
  inline void my_fn()
  {
    // magic happens
  }
};

Related questions

Using G++ to compile multiple .cpp and .h files

I've just inherited some C++ code that was written poorly with one cpp file which contained the main and a bunch of other functions. There are also .h files that contain classes and their function definitions. Until now the program …

Read More
*.h or *.hpp for your class definitions

I've always used a *.h file for my class definitions, but after reading some boost library code, I realised they all use *.hpp. I've always had an aversion to that file extension, I think mainly because I'm not used to …

Read More
Where does Visual Studio look for C++ header files?

I checked out a copy of a C++ application from SourceForge (HoboCopy, if you're curious) and tried to compile it. Visual Studio tells me that it can't find a particular header file. I found the file in the source tree, …

Read More