In app.h, you should forward-declare "typedef struct bintree_t bintree;" Then, in each source file that #includes "app.h" and also CALLS binary-tree-related f

In app.h, you should forward-declare "typedef struct bintree_t bintree;" Then, in each source file that #includes "app.h" and also CALLS binary-tree-related functions, you #include "bintree.h". Like I said, this is more of a concern in C++ where compile times are way, way slower than C. And in C++, it's very much worth it to forward declare in header files. It makes a big difference once your source code base has grown to epic proportions.