[CMake] General questions

[Yang Zhang]

Yang Zhang wrote:
> Hi, thanks for your reply.
> 
> Mike Jackson wrote:
>  >
>  > -- Mike Jackson   Senior Research Engineer
>  > Innovative Management & Technology Services
>  >
>  >
>  > On Feb 23, 2008, at 4:34 AM, Yang Zhang wrote:
>  >> - Can cmake auto-generate and cache transitive dependencies via
>  >> #includes (best described in Peter Miller's paper "Recursive Make
>  >> Considered Harmful")?
>  >
>  > I have no idea what a ransitive dependencies is, BUT cmake is more than
>  > capable of generating custom header files based on input from the cmake
>  > files. Look at the "CONFIGURE_FILE" command. run "cmake --help-command
>  > CONFIGURE_FILE" in a terminal.
> 
> That wasn't quite what I was asking, but I *think* the wiki has answered 
> my question:
> 
> "Auto depend information for C++, C, and Fortran"

Argh. I just did a little test where this feature seems to only work 
partially. Here, we see it working:

   $ mkdir test

   $ cd test

   $ mkdir inc

   $ echo 'int main() { return 0; }' > inc/a.h

   $ echo '#include "a.h"' > a.c

   $ cat > CMakeLists.txt
   project(a)
   add_executable(a a.c)
   include_directories(inc)

   $ cmake .
   -- Check for working C compiler: /usr/bin/gcc
   -- Check for working C compiler: /usr/bin/gcc -- works
   -- Check size of void*
   -- Check size of void* - done
   -- Check for working CXX compiler: /usr/bin/c++
   -- Check for working CXX compiler: /usr/bin/c++ -- works
   -- Configuring done
   -- Generating done
   -- Build files have been written to: /home/yz/test

   $ make
   Scanning dependencies of target a
   [100%] Building C object CMakeFiles/a.dir/a.o
   Linking C executable a
   [100%] Built target a

   $ make
   [100%] Built target a

   $ touch inc/a.h

   $ make
   Scanning dependencies of target a
   [100%] Building C object CMakeFiles/a.dir/a.o
   Linking C executable a
   [100%] Built target a

   $ make
   [100%] Built target a

However, the following doesn't work (imagine now that a.h is a header 
I'm working on, shared by multiple projects in /usr/local/include):

   $ make clean

   $ cat > CMakeLists.txt
   project(a)
   add_executable(a a.c)

   $ cmake .
   -- Configuring done
   -- Generating done
   -- Build files have been written to: /home/yz/test

   $ CPATH=inc make
   Scanning dependencies of target a
   [100%] Building C object CMakeFiles/a.dir/a.o
   Linking C executable a
   [100%] Built target a

   $ CPATH=inc make
   [100%] Built target a

   $ touch inc/a.h

   $ CPATH=inc make
   [100%] Built target a

It appears that cmake doesn't know where the header files are actually 
located, and hence is unable to add a proper dependency. I'm hoping to 
avoid specifying the same include_directories(...) for all projects that 
I'm working on. I've recently been surviving on an an ad-hoc build 
system that uses gcc -M, which specifies full paths, but that's tied to 
the compiler, of course.

-- 
Yang Zhang
http://www.mit.edu/~y_z/