链接CompactNSearch库时遇构造函数未定义引用错误求助

问题描述 #

使用CompactNSearch库时，编译阶段出现未解决的链接错误，耗时数小时未修复。

最小可复现示例（MWE） #

目录结构 #

克隆库后的目录结构如下：

├── CMakeLists.txt
├── CompactNSearch 
...
└── main.cpp

main.cpp代码 #

#include "CompactNSearch.h"
using namespace CompactNSearch;

int main()
{
    float r = 0;
    NeighborhoodSearch nsearch(r);
}

CMakeLists.txt代码 #

cmake_minimum_required(VERSION 3.22)

project(MyProject VERSION 1.0
                  LANGUAGES CXX)

add_executable(
    MyProject main.cpp
)

add_subdirectory(CompactNSearch)
target_link_libraries(MyProject CompactNSearch)

操作步骤 #

mkdir build
cd build
cmake ..
make

编译报错信息 #

[ 16%] Building CXX object CompactNSearch/CMakeFiles/CompactNSearch.dir/src/CompactNSearch.cpp.o
[ 33%] Linking CXX static library libCompactNSearch.a
[ 33%] Built target CompactNSearch
[ 50%] Building CXX object CMakeFiles/MyProject.dir/main.cpp.o
[ 66%] Linking CXX executable MyProject
/usr/bin/ld: CMakeFiles/MyProject.dir/main.cpp.o: in function `main':
main.cpp:(.text+0x44): undefined reference to `CompactNSearch::NeighborhoodSearch::NeighborhoodSearch(float, bool)'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/MyProject.dir/build.make:100: MyProject] Error 1
make[1]: *** [CMakeFiles/Makefile2:117: CMakeFiles/MyProject.dir/all] Error 2
make: *** [Makefile:136: all] Error 2

已尝试的解决方法 #

• 尝试多种CMake链接库的写法
• 分别将库编译为静态/共享库后再链接，结果一致
• 在构造函数定义中添加#error This should be shown，确认该代码已被编译

解决方案 #

问题根源是CompactNSearch库通过编译flag控制精度类型（float/double），默认启用double精度，与代码中传入float参数的构造函数不匹配。修改CMakeLists.txt，在引入子目录前添加精度控制flag即可解决：

cmake_minimum_required(VERSION 3.22)

project(MyProject VERSION 1.0
                  LANGUAGES CXX)

# 强制使用float精度，匹配代码中的参数类型
set(USE_DOUBLE_PRECISION OFF)

add_executable(
    MyProject main.cpp
)

add_subdirectory(CompactNSearch)
target_link_libraries(MyProject CompactNSearch)

内容的提问来源于stack exchange，提问作者Hakka