1. CMAKE_PREFIX_PATH

CMAKE_PREFIX_PATH 是一个分号分隔的路径列表，用来指明软件/库安装路径前缀，以供 find_package() ， find_program() ， find_library() ， find_file() 和 find_path() 命令搜索使用，这样就方便搜索可执行文件、头文件、库文件及相关配置文件等。

CMAKE_PREFIX_PATH文档

2. 演示

笔者将 Eigen-3.4.0 安装在了 /opt/eigen-3.4.0 目录下，在使用时可以这样写 CMakeLists.txt

cmake_minimum_required(VERSION 3.5)
project(program LANGUAGES CXX)
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
list(APPEND CMAKE_PREFIX_PATH "/opt/eigen-3.4.0") # 安装路径前缀
find_package(Eigen3 REQUIRED)
include_directories(${EIGEN3_INCLUDE_DIR})
message("** Found Eigen3 in: ${EIGEN3_ROOT_DIR}")
add_executable(${PROJECT_NAME} main.cpp)
命令cmake运行日志
-- The CXX compiler identification is GNU 9.4.0
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
** Found Eigen3 in: /opt/eigen-3.4.0
-- Configuring done
-- Generating done
-- Build files have been written to: (这个路径内容太长，删掉了)
测试程序如下
#include <iostream>
#include <Eigen/Eigen>
int main(int argc, char* argv[])
    std::cout << "Eigen3 version is : " 
              << EIGEN_WORLD_VERSION << "." 
              << EIGEN_MAJOR_VERSION << "." 
              << EIGEN_MINOR_VERSION << std::endl;
    return 0;