Conan+CMake项目链接报错：undefined reference to company_name::square

错误信息 #

执行cmake --build时出现以下链接错误：

[ 50%] Building CXX object CMakeFiles/exp_proj.dir/main.cpp.o
[100%] Linking CXX executable exp_proj
CMakeFiles/exp_proj.dir/main.cpp.o: In function `main':
main.cpp:(.text.startup+0x18d): undefined reference to `company_name::square(int)'
collect2: error: ld returned 1 exit status
gmake[2]: *** [CMakeFiles/exp_proj.dir/build.make:98: exp_proj] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/exp_proj.dir/all] Error 2
gmake: *** [Makefile:136: all] Error 2

项目代码与配置 #

主项目 #

main.cpp

#include <fmt/core.h>
#include <fmt/color.h>
#include <functions.h>
#include <iostream>

using namespace std;

int main() {
#ifdef NDEBUG
   {
      fmt::print(fmt::bg(fmt::color::crimson) | fmt::fg(fmt::color::black), "VERSION 1.0");
      fmt::print(fmt::fg(fmt::color::crimson), "\n\nRELEASE BUILD...");
      fmt::print(" the release build of the version 1.0 of the program runs with no issues!\nThe square of 5 is {}\n\n", company_name::square(5));

   }
#else
   fmt::print(fmt::bg(fmt::color::cornflower_blue) | fmt::fg(fmt::color::white), "VERSION 1.0");
   fmt::print(fmt::fg(fmt::color::cornflower_blue), "\n\nDEBUG BUILD... ");
   fmt::print(" the debug build of version 1.0 of the program runs with no issues!\nThe square of 5 is {}\n\n", company_name::square(5));


#endif
   return 0;
}

conanfile.py

from conan import ConanFile
from conan.tools.cmake import CMakeToolchain, CMake, CMakeDeps, cmake_layout

class project(ConanFile):
    name="exp_proj"
    version = "1.0"
    author = "SIGNORI Gianmario gianmario.signori@company_name.com"
    description = "IDK how many project I have done so far because of some unresolvable errors"
    topics = ("Conan", "Artifactory", "Libraries")
    exports_sources = "main.cpp", "CMakeLists.txt"
    settings = "os", "compiler", "build_type", "arch"
    options = {"shared": [True, False], "fPIC": [True, False]}
    default_options = {"shared": False, "fPIC": True}
    requires = (
        "fmt/10.1.1",
        "maths/1.0"
    )

    def config_options(self):
        if self.settings.os == "Windows":
            del self.options.fPIC

    def layout(self):
        cmake_layout(self)

    def generate(self):
        deps = CMakeDeps(self)
        deps.generate()
        tc = CMakeToolchain(self)
        tc.generate()

    def build(self):
        cmake = CMake(self)
        cmake.configure()
        cmake.build()

    def package(self):
        cmake = CMake(self)
        cmake.install()

CMakeLists.txt

cmake_minimum_required(VERSION 3.20)
project(exp_proj)

find_package(fmt REQUIRED)
find_package(maths REQUIRED)

set(CMAKE_CXX_STANDARD 20)

add_executable(exp_proj main.cpp)

target_link_libraries(exp_proj
      PRIVATE
         fmt::fmt
         maths::maths
)


install(TARGETS exp_proj DESTINATION bin)

自定义maths库 #

functions.cpp

#include "functions.h"

namespace company_name
{
   int square(int x)
   {
      return x*x;
   }
}

functions.h

#ifndef MATHS_FUNCTIONS_H
#define MATHS_FUNCTIONS_H

namespace company_name{
   int square(int x);
}

#endif//MATHS_FUNCTIONS_H

CMakeLists.txt

cmake_minimum_required(VERSION 3.20)
project(maths)

set(CMAKE_CXX_STANDARD 20)

add_library(maths STATIC functions.cpp)

target_include_directories(maths PUBLIC
      ${CMAKE_CURRENT_SOURCE_DIR}
)


install(TARGETS maths
      ARCHIVE DESTINATION lib
      INCLUDES DESTINATION include
)

install(FILES functions.h DESTINATION include)
install(TARGETS maths DESTINATION lib)

conanfile.py

from conan import ConanFile
from conan.tools.cmake import CMakeToolchain, CMake, CMakeDeps, cmake_layout
from conan.tools.files import copy

class maths(ConanFile):
    name="maths"
    version="1.0"
    author="SIGNORI GIANMARIO gianmario.signori@company_name.com"
    exports_sources="CMakeLists.txt", "functions.h", "functions.cpp"
    settings="os", "compiler", "build_type", "arch"
    options={"shared": [True, False]}
    default_options={"shared": False}

    def layout(self):
        cmake_layout(self)

    def generate(self):
        deps = CMakeDeps(self)
        deps.generate()
        tc=CMakeToolchain(self)
        tc.generate()

    def build(self):
        cmake=CMake(self)
        cmake.configure()
        cmake.build()

    def package(self):
        #copy(self, "*.h", dst="include", src=self.source_folder)
        #copy(self, "*.a", dst="lib", src=self.build_folder)
        #copy(self, "*.lib", dst="lib", src=self.build_folder)
        #copy(self, "*.cpp", self.source_folder, self.package_folder)
        #copy(self, "CMakeLists.txt", self.source_folder, self.package_folder)
        cmake = CMake(self)
        cmake.install()

    #def package_info(self):
     #   self.cpp_info.libs = ["maths"]

执行命令 #

$ conan install . -s build_type=...
$ cmake -S . -B build/... -DCMAKE_TOOLCHAIN_FILE=build/.../generators/conan_toolchain.cmake -DCMAKE_BUILD_TYPE=...
$ cmake --build build/...
$ ./build/.../"exp_proj"

其中...为Release/Debug构建的占位符。

问题排查与解决方案 #

核心问题 #

链接错误提示undefined reference，说明主项目编译时能找到头文件，但链接阶段找不到maths库的二进制符号。原因是maths库的Conan包未正确导出库信息，导致主项目CMake无法正确关联到maths库文件。

修复步骤 #

1. 启用maths库的package_info方法
   打开maths库的conanfile.py，取消注释package_info部分：

   def package_info(self):
       self.cpp_info.libs = ["maths"]
   

   这个方法告诉Conan将maths库添加到依赖项目的链接路径中，确保CMake能找到并链接该库。

2. 重新打包并安装maths库
   在maths库目录下执行：

   conan create . -s build_type=Release
   conan create . -s build_type=Debug
   

   这会重新生成包含正确库信息的Conan包，并安装到本地缓存。

3. 清理主项目构建缓存并重新构建
   删除主项目的build目录，重新执行：

   conan install . -s build_type=...
   cmake -S . -B build/... -DCMAKE_TOOLCHAIN_FILE=build/.../generators/conan_toolchain.cmake -DCMAKE_BUILD_TYPE=...
   cmake --build build/...
   

额外验证点 #

• 检查maths库的安装包路径（通常在~/.conan/data/maths/1.0/...），确认lib目录下存在libmaths.a（Linux/macOS）或maths.lib（Windows），include目录下存在functions.h。
• 主项目执行cmake --build时，查看链接命令是否包含-lmaths（Linux/macOS）或maths.lib（Windows）。

内容的提问来源于stack exchange，提问作者Gianmario Signori