CMake Can't Find Boost When Changing Visual Studio Target - c++

Question

I am following the instructions from https://badprog.com/c-boost-setting-up-on-windows-10 . I have Visual Studio 2017 installed, and installed boost_1_71_0-msvc-14.1-64.exe. CMake was downloaded from cmake.org/download/, cmake-3.19.0-rc1-win64-x64.msi.
I have a project that needs Boost Beast, which I believe is 1.70 or higher.
When I run cmake . everything seems fine:
C:\Users\Public\xyz>cmake .
-- Building for: Visual Studio 16 2019
-- Selecting Windows SDK version 10.0.17763.0 to target Windows 10.0.18362.
-- The CXX compiler identification is MSVC 19.24.28314.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/BuildTools/VC/Tools/MSVC/14.24.28314/bin/Hostx64/x64/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - not found
-- Found Threads: TRUE
-- Found Boost: C:/local/boost_1_71_0 (found suitable version "1.71.0", minimum required is "1.70") found components: thread system chrono date_time atomic
-- Configuring done
-- Generating done
-- Build files have been written to: C:/Users/Public/xyz
The resulting project opens in Visual Studio 2017, but then complains it needs the 2019 build tools. Surprisingly, as you can see above, it's building for Visual Studio 2019?
But, after killing CMakeCache.txt and CMakeFiles, if I do this:
C:\Users\Public\xyz>cmake -G "Visual Studio 15 2017" .
-- Selecting Windows SDK version 10.0.17763.0 to target Windows 10.0.18362.
-- The CXX compiler identification is MSVC 19.16.27034.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.16.27023/bin/Hostx86/x86/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - not found
-- Found Threads: TRUE
CMake Error at C:/Program Files/CMake/share/cmake-3.19/Modules/FindPackageHandleStandardArgs.cmake:218 (message):
Could NOT find Boost (missing: thread system) (found suitable version
"1.71.0", minimum required is "1.70")
Call Stack (most recent call first):
C:/Program Files/CMake/share/cmake-3.19/Modules/FindPackageHandleStandardArgs.cmake:577 (_FPHSA_FAILURE_MESSAGE)
C:/Program Files/CMake/share/cmake-3.19/Modules/FindBoost.cmake:2176 (find_package_handle_standard_args)
CMakeLists.txt:29 (FIND_PACKAGE)
-- Configuring incomplete, errors occurred!
See also "C:/Users/Public/xyz/CMakeFiles/CMakeOutput.log".
Suddenly it can't find Boost components (but can find Boost?). I've tried various forms of -DBOOST_LIBRARYDIR or -DBOOST_ROOT, etc., to no avail, but I don't seem to have the usual stackoverflow problem of cmake not being able to find Boost; instead it doesn't seem to recognize the Visual Studio 2017 target, despite having been installed for msvc-14.1?
CMakeLists.txt:
# Specify the minimum version for CMake
cmake_minimum_required(VERSION 3.1)
# Force C++11, for Boost Beast (async http library)
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)
# Project's name
project(xyz
VERSION 0.1
LANGUAGES CXX)
# Set the output folder where the program will be created
set(CMAKE_BINARY_DIR ${CMAKE_SOURCE_DIR}/build)
set(EXECUTABLE_OUTPUT_PATH ${CMAKE_BINARY_DIR})
set(LIBRARY_OUTPUT_PATH ${CMAKE_BINARY_DIR})
# Specify .cpp and .hpp is in src/
set(PROJECT_SOURCE_DIR ${CMAKE_SOURCE_DIR}/src)
include_directories("${PROJECT_SOURCE_DIR}")
# Add source to build target for hello world...
add_executable(main ${PROJECT_SOURCE_DIR}/main.cpp)
# Testing http support
ADD_EXECUTABLE( server ${PROJECT_SOURCE_DIR}/server.cpp )
FIND_PACKAGE( Boost 1.70 REQUIRED COMPONENTS thread system )
INCLUDE_DIRECTORIES( ${Boost_INCLUDE_DIRS} )
target_link_libraries ( server LINK_PUBLIC ${Boost_LIBRARIES} )

Answer 1

In the end, the issue was simple. If I may so, it was an easy mistake for a beginner to make but almost impossible for a beginner to unravel with regular google searching.
When I issued cmake ., it was defaulting to a 64 bit build, but assuming a Visual Studio 2019 target. That was wrong.
The equivalent should have been cmake -G "Visual Studio 15 2017 Win64" . But not knowing this, and following the wrong tutorials, I was issuing instead cmake -G "Visual Studio 15 2017" .. This defaulted to a 32 bit build - though by default it never mentions this fact. It could find boost, but all library files were for 64 bit and useless for 32 bit, so it simply said "I can't find anything!".
My thanks to #Tsyvarev, who should get the credit for the answer. Turning on DEBUG and looking at searched library files character by character was indeed the right call.