using find_package in cmakelists.txt

[Bowen Xu]

Hi,

I'm trying to use find_package(Zmqpp REQUIRED) in a CMakeLists.txt file, but it failed.
To import ZeroMQ, currently we have to use PkgConfig, that is,

find_package(PkgConfig REQUIRED)
pkg_check_modules(ZMQ REQUIRED libzmq)

however, even this does not work for zmqpp.
For example, if we have

find_package(PkgConfig REQUIRED)
pkg_check_modules(ZMQPP REQUIRED libzmqpp)
message("ZMQPP_INCLUDE_DIRS: ${ZMQPP_INCLUDE_DIRS}")
message("ZMQPP_LIBRARIES: ${ZMQPP_LIBRARIES}")

It prints out

ZMQPP_INCLUDE_DIRS: /usr/local/include;/opt/homebrew/Cellar/zeromq/4.3.5_1/include;/opt/homebrew/Cellar/libsodium/1.0.19/include
ZMQPP_LIBRARIES: zmqpp;zmq

The include path of zmqpp seems to be /usr/local/include, which is wrong in MacOS. (PS, I used brew install zmqpp to install the library). I guess this is a bug.

Another issue occurs to me: Can we simply use find_package(Zmqpp REQUIRED) to import the library?

Here is the cmake file I wrote:
(file path: ./cmake/FindZmqpp.cmake)

# - Try to find Zmqpp headers and libraries
#
# Usage of this module as follows:
#
# find_package(Zmqpp)
#
# Variables used by this module, they can change the default behaviour and need
# to be set before calling find_package:
#
# Zmqpp_ROOT_DIR  Set this variable to the root installation of
# Zmqpp if the module has problems finding
# the proper installation path.
#
# Variables defined by this module:
#
# Zmqpp_FOUND              System has Zmqpp libs/headers
# Zmqpp_LIBRARIES          The Zmqpp libraries
# Zmqpp_INCLUDE_DIR        The location of Zmqpp headers
# Zmqpp_VERSION            The version of Zmqpp

find_path(Zmqpp_ROOT_DIR
    NAMES include/zmqpp/zmqpp.hpp
)

message("Zmqpp_ROOT_DIR: ${Zmqpp_ROOT_DIR}")
find_library(Zmqpp_LIBRARY
        NAMES zmqpp libzmqpp
        HINTS ${ZeroMQ_ROOT_DIR}/lib
)

find_path(Zmqpp_INCLUDE_DIR
    NAMES zmqpp/zmqpp.hpp
    HINTS ${Zmqpp_ROOT_DIR}/include
)
message("Zmqpp_ROOT_DIR: ${Zmqpp_ROOT_DIR}")

function(extract_version_value value_name file_name value)
    file(STRINGS ${file_name} val REGEX "${value_name} .")
    string(FIND ${val} " " last REVERSE)
    string(SUBSTRING ${val} ${last} -1 val)
    string(STRIP ${val} val)
    set(${value} ${val} PARENT_SCOPE)
endfunction(extract_version_value)

extract_version_value("ZMQPP_VERSION_MAJOR" ${Zmqpp_INCLUDE_DIR}/zmqpp/zmqpp.hpp MAJOR)
extract_version_value("ZMQPP_VERSION_MINOR" ${Zmqpp_INCLUDE_DIR}/zmqpp/zmqpp.hpp MINOR)
extract_version_value("ZMQPP_VERSION_REVISION" ${Zmqpp_INCLUDE_DIR}/zmqpp/zmqpp.hpp REVISION)

set(Zmqpp_VER "${MAJOR}.${MINOR}.${REVISION}")

# We are using the 2.8.10 signature of find_package_handle_standard_args,
# as that is the version that ParaView 5.1 && VTK 6/7 ship, and inject
# into the CMake module path. This allows our FindModule to work with
# projects that include VTK/ParaView before searching for Remus
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(
    Zmqpp
    REQUIRED_VARS Zmqpp_LIBRARY Zmqpp_INCLUDE_DIR
    VERSION_VAR Zmqpp_VER
)

set(Zmqpp_FOUND ${ZEROMQ_FOUND})
set(Zmqpp_INCLUDE_DIRS ${Zmqpp_INCLUDE_DIR})
set(Zmqpp_LIBRARIES ${Zmqpp_LIBRARY})
set(Zmqpp_VERSION ${Zmqpp_VER})

mark_as_advanced(
    Zmqpp_ROOT_DIR
    Zmqpp_LIBRARY
    Zmqpp_LIBRARY_DEBUG
    Zmqpp_LIBRARY_RELEASE
    Zmqpp_INCLUDE_DIR
    Zmqpp_VERSION
)

To use it, an additional line is added to CMakeLists.txt:

set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake/")
find_package(Zmqpp REQUIRED)

This works well in my computer.

This is just my solution for the moment. Can this feature be supported by the zmqpp official repo?