项目同时依赖gflags和glog时CMake构建失败的解决方法

我有一个同时依赖gflags和glog的C++项目，相关代码及操作如下：

我的CMakeLists.txt #

cmake_minimum_required(VERSION 3.23.2)

project(demo)

include(FetchContent)

FetchContent_Declare(gflags
  URL      https://github.com/gflags/gflags/archive/v2.2.2.zip
  URL_HASH SHA256=19713a36c9f32b33df59d1c79b4958434cb005b5b47dc5400a7a4b078111d9b5
)
FetchContent_MakeAvailable(gflags)
include_directories(${gflags_BINARY_DIR}/include)


FetchContent_Declare(glog
  URL      https://github.com/google/glog/archive/v0.4.0.zip
  URL_HASH SHA256=9e1b54eb2782f53cd8af107ecf08d2ab64b8d0dc2b7f5594472f3bd63ca85cdc
)
FetchContent_MakeAvailable(glog)
include_directories(${glog_SOURCE_DIR}/src ${glog_BINARY_DIR})

add_executable(demo demo.cc)
target_link_libraries(demo glog::glog)

我的demo.cc #

#include <iostream>
using namespace std;

#include <glog/logging.h>


int main(int argc, char** argv){
    gflags::ParseCommandLineFlags(&argc, &argv, true);
    google::InitGoogleLogging(argv[0]);
    LOG(INFO) << "This is INFO log information";
    return 0;
}

构建命令及错误 #

执行构建命令：

mkdir -p build
cd build
cmake ..

执行后出现如下错误：

CMake Error in build/_deps/glog-src/CMakeLists.txt:
  export called with target "glog" which requires target
  "gflags_nothreads_static" that is not in this export set, but in multiple
  other export sets:
  .../build/_deps/gflags-build/gflags-nonamespace-targets.cmake,
  .../build/_deps/gflags-build/gflags-targets.cmake.


  An exported target cannot depend upon another target which is exported
  multiple times.  Consider consolidating the exports of the
  "gflags_nothreads_static" target to a single export.

请问如何通过修改我自己的CMakeLists.txt来消除上述错误？

错误根源是gflags 2.2.2版本默认会生成带命名空间和不带命名空间的两套导出目标，导致glog依赖的gflags目标被重复导出，触发CMake的检查错误。

修改CMakeLists.txt，在拉取gflags前添加set(gflags_NAMESPACE gflags)，强制gflags只生成带命名空间的目标，避免重复导出：

cmake_minimum_required(VERSION 3.23.2)

project(demo)

include(FetchContent)

# 强制gflags只生成带命名空间的目标，避免重复导出
set(gflags_NAMESPACE gflags)

FetchContent_Declare(gflags
  URL      https://github.com/gflags/gflags/archive/v2.2.2.zip
  URL_HASH SHA256=19713a36c9f32b33df59d1c79b4958434cb005b5b47dc5400a7a4b078111d9b5
)
FetchContent_MakeAvailable(gflags)

FetchContent_Declare(glog
  URL      https://github.com/google/glog/archive/v0.4.0.zip
  URL_HASH SHA256=9e1b54eb2782f53cd8af107ecf08d2ab64b8d0dc2b7f5594472f3bd63ca85cdc
)
FetchContent_MakeAvailable(glog)

add_executable(demo demo.cc)
# 显式链接gflags目标，代码中直接调用了gflags API
target_link_libraries(demo glog::glog gflags::gflags)
# 使用target_include_directories替代全局include，避免污染全局路径
target_include_directories(demo PRIVATE 
  ${gflags_BINARY_DIR}/include
  ${glog_SOURCE_DIR}/src 
  ${glog_BINARY_DIR}
)

另外补充两点优化：

• 替换全局include_directories为target_include_directories，仅给当前目标添加包含路径，符合CMake现代实践。
• 显式添加gflags::gflags到链接库列表，因为代码直接调用了gflags的API，需要明确依赖关系。

内容的提问来源于stack exchange，提问作者aban