SF.5: Add recommendation, that a .cpp file should include the .h file(s) that defines its interface at first.

[ksdd]

Including the interface defining header(s) at first ensures, that the header(s) are self-sufficient. Example:

// foo.h
int mean(const std::vector v);

// foo.cpp - bad include order

include

include <foo.h>

Missing include of vector in foo.h is undiscovered until other users may stumble over it. By including foo.h first the implementer immediately encouters this problem.

[gdr-at-ms]

Components are not always neatly divided into A.h/A.cxx one-to-one correspondence. Furthermore, if A.h contains the interface of component A, then it should be self-contained.