CMake：不能 link 使用共享 zlib 包装器库的简单项目

Question

在我的情况下，我有两个 CMake 项目（如果重要的话，使用 MSYS Makefiles 构建）：

一个是共享库，使用 Zlib 和 Libzip 为库用户提供压缩功能，我们称它为 mylib.
另一个应用程序使用 mylib 来执行一些压缩操作。它不必担心 Zlib、Libzip 或任何东西。我们称它为 app.

我在下面创建了一个简单的示例来演示我遇到的奇怪问题。简单地说，app 在运行 make 时拒绝 link，但前提是某些 Libzip 代码在 mylib（编译并且link没问题，无论如何）。

Zlib 和 Libzip 源代码位于 C:/Dev/Libs.

lib/CMakeLists.txt

cmake_minimum_required(VERSION 3.7)

# Set project
project(mylib)
set(LIBS_DIR "C:/Dev/Libs")

# Add mylib sources
include_directories("${CMAKE_CURRENT_SOURCE_DIR}/src")
file(GLOB_RECURSE SRCS "src/*.cpp")
add_library(mylib SHARED ${SRCS})

# Add Zlib
set(ZLIB_ROOT "${LIBS_DIR}/zlib-1.2.11")
include_directories(${ZLIB_ROOT})
target_include_directories(mylib PUBLIC ${ZLIB_ROOT})
file(GLOB ZLIB_SRCS "${ZLIB_ROOT}/*.c")
add_library(zlib STATIC ${ZLIB_SRCS})

# Add Libzip
set(LIBZIP_ROOT "${LIBS_DIR}/libzip-1.1.3")
include_directories("${LIBZIP_ROOT}/lib")
target_include_directories(mylib PUBLIC "${LIBZIP_ROOT}/lib")
file(GLOB LIBZIP_SRCS "${LIBZIP_ROOT}/lib/*.c")
add_library(libzip STATIC ${LIBZIP_SRCS})

set(LIBS_LINK    zlib libzip)
set(LIBS_INSTALL zlib libzip)
set(LIBS_EXPORT  zlib libzip)
target_link_libraries(mylib PUBLIC ${LIBS_LINK})

# https://rix0r.nl/blog/2015/08/13/cmake-guide/
# Define headers for this library. PUBLIC headers are used for
# compiling the library, and will be added to consumers' build
# paths.
target_include_directories(mylib PUBLIC
    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
    $<INSTALL_INTERFACE:include>
    PRIVATE src)

# 'make install' to the correct locations (provided by GNUInstallDirs).
include(GNUInstallDirs)
install(TARGETS mylib ${LIBS_INSTALL} EXPORT mylibConfig
        ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
        LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
        RUNTIME DESTINATION ${CMAKE_CURRENT_BINARY_DIR})  # This is for Windows
install(DIRECTORY include/ DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})

# This makes the project importable from the install directory
# Put config file in per-project dir (name MUST match), can also
# just go into 'cmake'.
install(EXPORT mylibConfig DESTINATION share/mylib/cmake)

# This makes the project importable from the build directory
export(TARGETS mylib ${LIBS_EXPORT} FILE mylibConfig.cmake)

lib/src/lib.hpp

#pragma once

namespace lib
{
    int func();
}

lib/src/lib.cpp

#include "lib.hpp"

#define ZIP_STATIC
#include "zip.h"

int lib::func()
{
    zip_source_t *src;
    zip_error_t error;
    src = zip_source_buffer_create(0, 1, 0, &error);

    return 10;
}

app/CMakeLists.txt

cmake_minimum_required(VERSION 3.7)

project(app)

# Add app sources
file(GLOB_RECURSE SRCS "src/*.cpp")
add_executable(app ${SRCS})

# Add mylib
set(mylib_DIR "${CMAKE_CURRENT_BINARY_DIR}/../lib")
find_package(mylib REQUIRED)
configure_file("${mylib_DIR}/libmylib.dll" "libmylib.dll" COPYONLY)
target_link_libraries(app mylib)

app/src/app.hpp

#pragma once
#include <lib.hpp>

app/src/app.cpp

#include <iostream>
#include "app.hpp"

int main()
{
    std::cout << lib::func() << std::endl;
    return 0;
}

构建 mylib

的输出

$ make
[ 13%] Built target zlib
[ 98%] Built target libzip
Scanning dependencies of target mylib
[ 99%] Building CXX object CMakeFiles/mylib.dir/src/lib.cpp.obj
[100%] Linking CXX shared library libmylib.dll
[100%] Built target mylib

构建 app

的输出

$ make
Scanning dependencies of target app
[ 50%] Building CXX object CMakeFiles/app.dir/src/app.cpp.obj
[100%] Linking CXX executable app.exe
CMakeFiles/app.dir/objects.a(app.cpp.obj):app.cpp:(.text+0x17): undefined reference to `lib::func()'
collect2.exe: error: ld returned 1 exit status
make[2]: *** [app.exe] Error 1
make[1]: *** [CMakeFiles/app.dir/all] Error 2
make: *** [all] Error 2

如果我在lib/src/lib.cpp中注释src = zip_source_buffer_create(0, 1, 0, &error);，重建然后重建应用:

$ make
-- Configuring done
-- Generating done
-- Build files have been written to: C:/Dev/Builds/cmaketest/app
[ 50%] Linking CXX executable app.exe
[100%] Built target app

$ ./app
10

产生了预期的结果。

问题一定出在 app 的 CMakeLists 中，因为 mylib 构建良好，没有任何 linking 错误。还是我在 mylib 中错误地添加了 zlib/libzip？我需要静态地 link 给他们，但我无法让它与 find_package 一起工作。

谢谢！

Answer 1

复制 .dll.a 文件后也能正常工作了：

configure_file("${mylib_DIR}/libmylib.dll.a" "libmylib.dll.a" COPYONLY)

并在 lib 中为我的所有方法添加以下前缀：

__declspec(dllexport)

CMake：不能 link 使用共享 zlib 包装器库的简单项目

CMake: Can't link simple project that uses shared zlib wrapper library

c++

zlib

cmake

libzip