cmka下切换使用不同版本的boost-未解决

前言

我大体知道问题在哪了：应该是自己编译的boost没有对应的cmake。需要先解决这个问题。我有时间来解决。

干活的时候，需要的是1.68版本的boost。我本机安装的1.71版本的boost。
一些代码和版本密切相关，比如：

#include <boost/version.hpp>
#if BOOST_VERSION <= 106800
#   include <boost/signals.hpp>
#else
# include <boost/asio/signal_set.hpp>
#endif
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所以，有必要在一台机器上灵活的切换使用不同的boost版本。
我当前的环境如下所示：

➜  uname -a
Linux dacao-VirtualBox 5.11.0-27-generic #29~20.04.1-Ubuntu SMP Wed Aug 11 15:58:17 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

➜ cmake --version                                                                                                                                    
cmake version 3.16.3
CMake suite maintained and supported by Kitware (kitware.com/cmake).

# sudo apt install libboost1.71-dev-all
➜ dpkg -S /usr/include/boost/version.hpp
libboost1.71-dev:amd64: /usr/include/boost/version.hpp
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而我们编译的程序如下所示，保存为boost_version.cpp。其中BOOST_SCOPE_EXITdeclares a scope exit.

#include <iostream>
#include <boost/scope_exit.hpp>

struct Object
{
    int i;
};


int main(void)
{
    struct Object* obj = new Object;
    BOOST_SCOPE_EXIT(obj) {
        delete obj;
        std::cout<<"obj has been released"<<std::endl;
    }BOOST_SCOPE_EXIT_END
    
    return 0;
}
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在cmake中查找boost库和头文件

参考：FindBoost - cmake
我们编写出如下的CMakeLists.txt：

cmake_minimum_required(VERSION 3.11)

project(boost_version)

find_package(
    Boost REQUIRED
    COMPONENTS program_options) # COMPONENTS用不着，为了编译复杂点，加上的

# include_directories(${Boost_INCLUDE_DIRS})

add_executable(${PROJECT_NAME} boost_version.cpp)

# target_link_libraries(${PROJECT_NAME} ${Boost_LIBRARIES})
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我们启用Boost_DEBUG选项，以看到查找Boost的输出。

➜  mkdir build && cd build
➜  cmake -DBoost_DEBUG=ON ..                                                                                                                          
-- Found Boost 1.71.0 at /usr/lib/x86_64-linux-gnu/cmake/Boost-1.71.0
--   Requested configuration: REQUIRED COMPONENTS program_options
-- BoostConfig: find_package(boost_headers 1.71.0 EXACT CONFIG REQUIRED  HINTS /usr/lib/x86_64-linux-gnu/cmake)
-- Found boost_headers 1.71.0 at /usr/lib/x86_64-linux-gnu/cmake/boost_headers-1.71.0
-- BoostConfig: find_package(boost_program_options 1.71.0 EXACT CONFIG REQUIRED  HINTS /usr/lib/x86_64-linux-gnu/cmake)
-- Found boost_program_options 1.71.0 at /usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0
-- Boost toolset is gcc9 (GNU 9.4.0)
-- Scanning /usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/libboost_program_options-variant*.cmake
--   Including /usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/libboost_program_options-variant-shared.cmake
--   [x] libboost_program_options.so.1.71.0
--   Including /usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/libboost_program_options-variant-static.cmake
--   [ ] libboost_program_options.a
-- Adding boost_program_options dependencies: headers
-- Configuring done
-- Generating done
-- Build files have been written to: /home/dacao/exercise/CPlusPlus/build
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可以看到，我们顺利的cmake中添加了查找boost的功能。

在cmake中查找boost库和头文件 – 自定义boost库和头文件位置 – 失败 – 未解决

首先，我们在Boost Version History中下载我们需要的版本。
然后，按照Getting Started on Unix Variants中的介绍，编译和安装boost。

➜  wget -c https://boostorg.jfrog.io/artifactory/main/release/1.68.0/source/boost_1_68_0.tar.gz
➜  tar -zxvf boost_1_68_0.tar.gz
➜  cd boost_1_68_0

➜  ./bootstrap.sh # 这设置了所有内容并构建`b2`了用于构建 Boost 的程序。
➜  ./b2 install --prefix=/home/dacao/exercise/boost #编译并安装到指定位置

➜ cd /home/dacao/exercise/boost && ls
include  lib # 分别存放boost的头文件和库
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按照FindBoost - cmake的文档介绍:
This module reads hints about search locations from variables:

BOOST_ROOT             - Preferred installation prefix
 (or BOOSTROOT)
BOOST_INCLUDEDIR       - Preferred include directory e.g. <prefix>/include
BOOST_LIBRARYDIR       - Preferred library directory e.g. <prefix>/lib
Boost_NO_SYSTEM_PATHS  - Set to ON to disable searching in locations not
                         specified by these hint variables. Default is OFF.
Boost_ADDITIONAL_VERSIONS
                       - List of Boost versions not known to this module
                         (Boost install locations may contain the version)
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所以，按理说，我们可以使用BOOST_ROOT指定我们的安装位置，使用Boost_NO_SYSTEM_PATHS指定不去查找系统的boost库，即可满足我们的需求。
然而，现实并非如此：

➜  cmake -DBoost_NO_SYSTEM_PATHS=ON -DBOOST_ROOT=/home/dacao/exercise/boost   -DBoost_DEBUG=ON ..
-- Found Boost 1.71.0 at /usr/lib/x86_64-linux-gnu/cmake/Boost-1.71.0
--   Requested configuration: REQUIRED COMPONENTS program_options
-- BoostConfig: find_package(boost_headers 1.71.0 EXACT CONFIG REQUIRED  HINTS /usr/lib/x86_64-linux-gnu/cmake)
-- Found boost_headers 1.71.0 at /usr/lib/x86_64-linux-gnu/cmake/boost_headers-1.71.0
-- BoostConfig: find_package(boost_program_options 1.71.0 EXACT CONFIG REQUIRED  HINTS /usr/lib/x86_64-linux-gnu/cmake)
-- Found boost_program_options 1.71.0 at /usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0
-- Boost toolset is gcc9 (GNU 9.4.0)
-- Scanning /usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/libboost_program_options-variant*.cmake
--   Including /usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/libboost_program_options-variant-shared.cmake
--   [x] libboost_program_options.so.1.71.0
--   Including /usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/libboost_program_options-variant-static.cmake
--   [ ] libboost_program_options.a
-- Adding boost_program_options dependencies: headers
-- Configuring done
-- Generating done
-- Build files have been written to: /home/dacao/exercise/CPlusPlus/build
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并没有去找我们指定的boost库。在CMakeCache.txt可以更加清楚的看到这一点。

//No help, variable specified on the command line.
BOOST_ROOT:UNINITIALIZED=/home/dacao/exercise/boost

//No help, variable specified on the command line.
Boost_DEBUG:UNINITIALIZED=ON

//The directory containing a CMake configuration file for Boost.
Boost_DIR:PATH=/usr/lib/x86_64-linux-gnu/cmake/Boost-1.71.0

//No help, variable specified on the command line.
Boost_NO_SYSTEM_PATHS:UNINITIALIZED=ON
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最后

我在网上搜了一圈，没有找见该咋整。
我搜到两个相关的问题： How can I get CMake to find my alternative Boost installation?、 CMake is not able to find BOOST libraries

如果要解决这个问题(需要时间和足够的耐心)，可以分为三步来考虑：

• 详细了解find_package，阅读查找过程。
• 分析sudo apt install libboost1.71-dev-all和./b2 installl的区别。
• 结合上面两步，分析出问题根源，并解决问题。

我们看下第二步，安装libboost1.71，到底安装了哪些东西。(最好看能不能找见包的构建过程，因为搜到一个比较有趣的东西boost-cmake)

➜ dpkg -L libboost1.71-all-dev 
/.
/usr
/usr/share
/usr/share/doc
/usr/share/doc/libboost1.71-all-dev
/usr/share/doc/libboost1.71-all-dev/copyright
/usr/share/doc/libboost1.71-all-dev/changelog.Debian.gz


➜  dpkg -L libboost1.71-dev:amd64
/usr/include/boost/**
# 下面这几行可能对解决问题，有用
/usr/lib/x86_64-linux-gnu/cmake/Boost-1.71.0
/usr/lib/x86_64-linux-gnu/cmake/Boost-1.71.0/BoostConfig.cmake
/usr/lib/x86_64-linux-gnu/cmake/Boost-1.71.0/BoostConfigVersion.cmake
/usr/lib/x86_64-linux-gnu/cmake/BoostDetectToolset-1.71.0.cmake
/usr/lib/x86_64-linux-gnu/cmake/boost_headers-1.71.0
/usr/lib/x86_64-linux-gnu/cmake/boost_headers-1.71.0/boost_headers-config-version.cmake
/usr/lib/x86_64-linux-gnu/cmake/boost_headers-1.71.0/boost_headers-config.cmake
/usr/share/doc/**
/usr/share/lintian/**

➜  dpkg -L libboost1.71-tools-dev
....

➜  dpkg -L libboost-program-options1.71-dev:amd64 
# 下面这几行可能对解决问题，有用
/usr/lib/x86_64-linux-gnu/cmake
/usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0
/usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/boost_program_options-config-version.cmake
/usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/boost_program_options-config.cmake
/usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/libboost_program_options-variant-shared.cmake
/usr/lib/x86_64-linux-gnu/cmake/boost_program_options-1.71.0/libboost_program_options-variant-static.cmake
/usr/lib/x86_64-linux-gnu/libboost_program_options.a

....
....
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问题解决