[CMake] Finding directories

[Chris Wood]

Hello all,

I'm trying to build a static library and use it for a compiling a
fortran file.  If I do:

set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR})
add_library(mylib STATIC ${lib_src}/mylib.for)
file(MAKE_DIRECTORY ${PROJECT_BINARY_DIR}/bin)
add_executable(bin/out ${PROJECT_SOURCE_DIR}/src/program.f)
target_link_libraries(bin/out mylib)

then it all works (note the library is built into the binary directory
root, but the fortran is compiled into a subdirectory); but, if I do

set(archives ${PROJECT_BINARY_DIR}/lib)
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/lib)
add_library(mylib STATIC ${lib_src}/mylib.for)
find_library(mylib NAMES mylib PATHS ${archives})
file(MAKE_DIRECTORY ${PROJECT_BINARY_DIR}/bin)
add_executable(bin/out ${PROJECT_SOURCE_DIR}/src/program.f)
target_link_libraries(bin/out mylib)

I get an error when I run cmake:

CMake Error: The following variables are used in this project, but
they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the
CMake files:
mylib
    linked by target "bin/out" in directory /home/chris/project

If I leave out the final 2 lines, then the archive file does get
written to the lib subdirectory, as libmylib.a as expected.  If I do

set(archives ${PROJECT_BINARY_DIR}/lib)
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/lib)
add_library(mylib STATIC ${lib_src}/mylib.for)
find_library(mylib NAMES mylib PATHS ${archives})
include_directories(${archives})
set(libs ${libs} ${mylib})
file(MAKE_DIRECTORY ${PROJECT_BINARY_DIR}/bin)
add_executable(bin/out ${PROJECT_SOURCE_DIR}/src/program.f)
target_link_libraries(bin/out {LIBS})

then the cmake command runs fine, but running make then generates
compile errors (I know the set command and target_link_libraries
variables are different cases - one of the things I don't understand
is why this only fails when make is run, instead of cmake; if the
variables are the same case, then I get the same error as above).

So, how can I get CMake to recognise my {PROJECT_BINARY_DIR}/lib
folder that is created during the CMake run? Can someone point out my
(probably obvious) mistake?!

Cheers,
Chris