用CMake编译和链接子项目库

我有2个项目（prj1和prj2）。一个（prj2）依赖于另一个（prj1）是静态库。我到达时用CMake分别编译它们。

但是我需要将一个（prj1）集成到另一个（prj2）。因此，我希望CMake在其他（prj2）之前先编译静态库（prj1），然后链接该静态库。我尝试了一些操作，但id无效。

• prj1“核心”是https://gitlab.com/RyDroid/PlanetWars2dRT-core
• prj2“ SDL2”是https://gitlab.com/RyDroid/PlanetWars2dRT-SDL2/（请参见分支添加核）

在prj2中，externals / core是git子模块（对于非git用户，您可以将此目录视为prj1的复制粘贴）。我在prj2“ SDL2”中尝试了此CMakeLists.txt（但没有成功）：

cmake_minimum_required(VERSION 2.8)


if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" OR
    "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
  set(CMAKE_CXX_FLAGS       "-Wall -Wextra -Wformat=2 -Wpedantic -D_FORTIFY_SOURCE=2")
  set(CMAKE_CXX_FLAGS_DEBUG "-O0 -g")
elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
  # TODO
endif()

set(CMAKE_CXX_FLAGS "-std=c++11 ${CMAKE_CXX_FLAGS}")
# if (CMAKE_VERSION VERSION_LESS "3.1")
#   if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR
#       CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
#     set (CMAKE_CXX_FLAGS "-std=c++11 ${CMAKE_CXX_FLAGS}")
#   endif()
# else()
#   set(CMAKE_CXX_STANDARD 11)
# endif()

project(PlanetWars2dRT-SDL2)

# Version number
set(VERSION_MAJOR "0")
set(VERSION_MINOR "0")
set(VERSION_MICRO "0")

# Configure a header file to pass some of the CMake settings
# to the source code.
configure_file (
  "src/compilation_config.h.in"
  "${PROJECT_BINARY_DIR}/compilation_config.h"
  )
# Add the binary tree to the search path for include files
# so that we will find compilation_config.h
include_directories("${PROJECT_BINARY_DIR}")

set(LIBRARY_OUTPUT_PATH    lib/${CMAKE_BUILD_TYPE})
set(EXECUTABLE_OUTPUT_PATH bin/${CMAKE_BUILD_TYPE})

include_directories(src/)
file(
  GLOB_RECURSE
  source_files
  src/*
  )
add_executable(planet-wars-2d-rt-sdl2 ${source_files})

#include(ExternalProject)
#ExternalProject_Add(PlanetWars2dRT PREFIX externals/core/)
include_directories(externals/core/src/utils/ externals/core/src/specific/)
add_subdirectory(externals/core/)
#find_package(PlanetWars2dRT-core REQUIRED)

include(FindPkgConfig)
pkg_search_module(SDL2 REQUIRED sdl2)
pkg_search_module(SDL2GFX REQUIRED SDL2_gfx)
include_directories(${SDL2_INCLUDE_DIRS} ${SDL2IMAGE_INCLUDE_DIRS})
target_link_libraries(
  planet-wars-2d-rt-sdl2
  planet-wars-2d-rt-core
  ${SDL2_LIBRARIES} ${SDL2GFX_LIBRARIES}
  )

那是prj2树的简化版本：

.
├── build (with CMake stuff generated with "cmake ..")
├── CMakeLists.txt
├── externals
│   └── core
│       ├── build (with CMake stuff generated with "cmake ..")
│       ├── CMakeLists.txt
│       ├── makefile
│       └── src
├── makefile
├── README.md
└── src
    ├── compilation_config.h.in
    └── planet-wars-2d-rt-sdl2.cpp

如何使用CMake编译prj2“ SDL2”中的prj1“ core”库，然后将prj1的库与prj2（再次使用CMake）链接？

如果您的解决方案不适用于非GNU / Linux操作系统，则不是大问题。注意：我的PC在Debian GNU / Linux 8“ Jessie”上运行。

问候。