Why tuple documentation for example says to use:
#include "boost/tuple/tuple.hpp"
and not
#include <boost/tuple/tuple.hpp>
I know that it's almost not probably my code will have also boost/tuple/tuple.hpp, but using include <> states explicitly not to look in the curent directory.
So what is the reason?
Afaik the reason is to differentiate between headers that belong to an application and those which are from external libraries. I can't say why they have not used this convention. It is a only a convention and not a rule.
Perhaps someone should raise this issue with the Boost maintainers?
The historical meaning of <somefile> is to look in the system-standard places. With "somefile" it means look in the current directory, plus some other places.
From msdn:
Quoted form
This form instructs the preprocessor to look for include files in the same directory of the file that contains the #include statement, and then in the directories of any files that include (#include) that file. The preprocessor then searches along the path specified by the /I compiler option, then along paths specified by the INCLUDE environment variable.
Angle-bracket form
This form instructs the preprocessor to search for include files first along the path specified by the /I compiler option, then, when compiling from the command line, along the path specified by the INCLUDE environment variable.
Are you asking what the difference between the two styles of inclusion is, or for Boost's rationale? Since others have spoken regarding the difference, I'll just add my take on the latter issue:
I don't believe either is more correct, in general. It depends on how your project is structured with respect to its dependencies. For example, in my projects I typically include the relevant bits of Boost, et cetera, in a subdirectory of the project and thus tend to prefer the #include "" form. If you want to pick up the Boost installation from a more global location, you'd prefer the #include <> form.
Using <> does not mean "don't look in the current directory" - It means look in an implementation defined place and then look somewhere else, also implementation defined. Either, both or neither of these could be the current directory. This is one of the more useless bits of the C++ standard.
Use <...> for boost. This is not Your code. Unless your code is boost.
Use "...." for your header files, which you inevitably have in every C++ program. This is for the reader, not for the compiler.