CMake build error: undefined reference to 'deflateEnd' - c++

Question

I'm trying to use zlib in my project. The CMakeLists.txt is as follows:
cmake_minimum_required(VERSION 3.5)
project(cmake-demo LANGUAGES CXX)
# The version number.
set(CMDemo_VERSION_MAJOR 0)
set(CMDemo_VERSION_MINOR 1)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
include(${PROJECT_SOURCE_DIR}/build/conan_paths.cmake)
set(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/build)
find_package(uwebsockets)
#ZLIB
if(ZLIB_FOUND)
set(INC_DIRS ${INC_DIRS} ${ZLIB_INCLUDE_DIRS})
set(LINK_LIBS ${LINK_LIBS} ${ZLIB_LIBS})
endif()
# Global approach
if(uwebsockets_FOUND)
set(INC_DIRS ${INC_DIRS} ${uwebsockets_INCLUDE_DIRS})
set(LINK_LIBS ${LINK_LIBS} ${uwebsockets_LIBS})
endif()
#libuv
if(libuv_FOUND)
set(INC_DIRS ${INC_DIRS} ${libuv_INCLUDE_DIRS})
set(LINK_LIBS ${LINK_LIBS} ${libuv_LIBS})
endif()
#usockets
if(usockets_FOUND)
set(INC_DIRS ${INC_DIRS} ${usockets_INCLUDE_DIRS})
set(LINK_LIBS ${LINK_LIBS} ${usockets_LIBS})
endif()
include_directories(${INC_DIRS})
add_executable(${PROJECT_NAME} main.cpp)
message("libs=${LINK_LIBS}")
target_link_libraries(${PROJECT_NAME} ${LINK_LIBS})
#output of message("${LINK_LIBS}")
C:/ProgramData/Miniconda3/Library/lib/z.lib;C:/Users/Sunway/.conan/data/libuv/1.41.0/_/_/package/9965605309592d7e617ec929633249a2031e4263/lib/libuv_a.a;C:/Users/Sunway/.conan/data/usockets/0.7.1/_/_/package/a24f5291464b4270092bce2e738cbf9f3cd53bb7/lib/libuSockets.a
I'm sure that ${LINK_LIBS} is correct, but it still doesn't work:
CMakeFiles/cmake-demo.dir/main.cpp.obj: In function `ZN3uWS15DeflationStreamD1Ev':
C:/Users/Sunway/.conan/data/uwebsockets/19.2.0/_/_/package/5ab84d6acfe1f23c4fae0ab88f26e3a396351ac9/include/uWebSockets/PerMessageDeflate.h:186: undefined reference to `deflateEnd'
os: Windows10 x64
IDE: QtCreator4.14.2
compiler: MinGW 32-bit

Answer 1

The thing is, that you have to set the path to the library file as the target_link_libraries argument.
According to the documentation, if you want to link the library, each argument of target_link_libraries can be:
A library target name
A full path to a library file (e.g. /usr/lib/foo.so)
A plain library name (e.g. foo)
In your case I suggest you to add the complete path to the library.
I don't have all the code of your project, so I suggest you consider this minimal example:
add_executable(test main.cpp)
SET (ZLIB_ROOT "/tmp/zlib")
SET (ZLIB_INCLUDE_DIR "/tmp/zlib/include/")
SET (ZLIB_LIBRARY "/tmp/zlib/lib/libz.so.1.2.11")
FIND_PACKAGE (ZLIB REQUIRED)
MESSAGE (" zlib version major is " ${ZLIB_VERSION_MAJOR})
MESSAGE (" zlib version minor is " ${ZLIB_VERSION_MINOR})
MESSAGE (" zlib include is " ${ZLIB_INCLUDE_DIR})
MESSAGE (" zlib libraries are " ${ZLIB_LIBRARIES})
target_link_libraries(test ${ZLIB_LIBRARIES})
After downloading the latest zlib release and installing it in /tmp, everything works as expected.
Update: as #uilianries mentioned, since you are using conan, you have cmake_find_package generator that defines variables with all the necessary paths. So you don't need to set the paths in CMakeLists.txt manually.

Answer 2

It is because the libzlib.a is for x86_64 while the compiler is MinGW-32bit; I solved the problem by execute the command
$conan install .. --build=missing --pr=x86_32
the x86_64 is a profile(x86) generated by conan.