[CMake] Library include path question

[Daniel Schepler]

How about something like (in the top-level directory for the projectlib sources):

add_library(projectlib STATIC projectlib/foo.h projectlib/foo.cpp ...)
target_include_directories(projectlib PUBLIC . PRIVATE projectlib)

(Note that this will add the top-level directory as well as the projectlib subdirectory for building projectlib sources - which is probably what you want in order to be able to resolve inter-header dependencies.)
--
Daniel Schepler
________________________________
From: CMake [cmake-bounces at cmake.org] on behalf of Chris Johnson [cxjohnson at gmail.com]
Sent: Monday, January 19, 2015 5:14 PM
To: cmake at cmake.org
Subject: [CMake] Library include path question

A common and useful method for avoiding name conflicts and keeping files well-organized is to place them in a subdirectory unique to the library.  For example, the libraries for Graphviz and Postgres often install their API header files in directories named <install-prefix>/include/graphviz and <install-prefix>/include/libpq.  So on my local development system, these libraries' API header files are in /usr/local/include/graphviz/*.h and /usr/local/include/libpq/*.h.

This is the convention that we use for our internal projects as well.

C++ code which needs to include these files by necessity must name that subdirectory.  For example, to use Postgres's API defined in libpq-fs.h, the C++ code must look like this:

#include <libpq/libpq-fs.h>

We do the same for our internal libraries, for example, to use the "projectlib" library from some program, the code would resemble:

#include <projectlib/foo.h>

In the library itself, however, the code is like this:

foo.h:
-----
class Foo {
public:
    Foo();
};

foo.cpp
-------
#include "foo.h"

Foo::Foo() {
 // constructor code
}
// etc.

That is, note that the header and source files are in the SAME directory.


CMake does not handle this well when trying to compile a program using the library.  CMake wants to look in the source directory or the build directory for the header file, and those directory paths do not have the "projectlib" prefix which is what the source code for the program expects (#include <projectlib/foo.h>).

I've kludged around this by adding a function which does some ugly directory creation in the build directory and then copies the headers to where the source expects to find them.

But I think there's something about CMake I am not understanding correctly, or a feature I should be using that I am unaware of, in order to make this all work without writing code in my CMakeLists.txt files to copy source files to expected places.  This library file layout for headers and source is very common in the Unix world, and we've modeled our largish (500 directories, dozens of libraries) project on it.

Is there something about CMake I need to learn to make this work more cleanly?


Thanks,
..chris






Most libraries correctly put their headers into ./include/<libdirname>
  39 # but CMake wants to look in the source or build dir, which doesn't have
  40 # <libdirname> as a prefix. That prefix is used in the source files in
  41 # their #include "libdirname/libheader.h" statements.  Headers will not be
  42 # found with that prefix when obtained from the source or build dir by CMake.

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