CMake 链接错误（未定义的引用）

我正在使用 SSL-Vision 软件。它有一个示例客户端，我一直试图将其与整个项目分开。我找到了自己编辑客户端所需的源代码，因此我只是从软件中复制它们并使用 CMake 来构建我的客户端。

下面的项目结构经过简化，缩小了问题范围（我相信！）。

.
├── CMakeLists.txt 
├── main.cc
├── build
│   ├── CMakeLists.txt
│   └── messages_ssl_... (.cc/.h, 4 each)
└── src
    ├── CMakeLists.txt
    └── (Other subdirs and sources/headers) 

./CMakeLists.txt:

cmake_minimum_required(VERSION 2.6)
project( TestClient )

find_package( PkgConfig REQUIRED )
pkg_check_modules( QTCORE_PKG QtCore )
include_directories( ${QTCORE_PKG_INCLUDE_DIRS} )

include(FindProtobuf)
find_package( Protobuf REQUIRED )
include_directories( ${PROTOBUF_INCLUDE_DIRS} )

find_package( PkgConfig REQUIRED )
pkg_check_modules( GLIB_PKG glib-2.0 ) 
include_directories( ${GLIB_PKG_INCLUDE_DIRS} )

include_directories( "src" ) 
add_subdirectory( src )

include_directories( "build" ) 
add_subdirectory( build )


add_executable( clientTest clientTest.cc )

target_link_libraries( clientTest robocup_ssl_client messages_robocup_ssl_detection.pb messages_robocup_ssl_geometry.pb messages_robocup_ssl_wrapper.pb messages_robocup_ssl_refbox_log.pb netraw robocup_ssl_client protobuf QtCore )

./build/CMakeLists.txt:

add_library( messages_robocup_ssl_detection.pb SHARED messages_robocup_ssl_detection.pb.cc )

add_library( messages_robocup_ssl_refbox_log.pb SHARED messages_robocup_ssl_refbox_log.pb.cc )

add_library( messages_robocup_ssl_geometry.pb SHARED messages_robocup_ssl_geometry.pb.cc )

add_library( messages_robocup_ssl_wrapper.pb SHARED messages_robocup_ssl_wrapper.pb.cc )

可能是缺失的#include in the messages_ssl_...文件，但它们都是自动生成的并且似乎是正确的。

In messages_robocup_ssl_detection.pb.h and messages_robocup_ssl_detection.pb.h仅包含 protobuf。

In messages_robocup_ssl_refbox_log.pb.h:

#include "messages_robocup_ssl_detection.pb.h"
// Other protobuf includes

In messages_robocup_ssl_wrapper.h:

#include "messages_robocup_ssl_detection.pb.h"
#include "messages_robocup_ssl_geometry.pb.h"
// Other protobuf includes

每个 .cc 文件中仅包含其标头和其他 protobuf 库。

最后，当我执行 make 时，会生成以下错误：

Linking CXX executable clientTest
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::ByteSize() const'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::MergeFrom(SSL_GeometryData const&)'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `protobuf_AddDesc_messages_5frobocup_5fssl_5fgeometry_2eproto()'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::Clear()'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::SSL_GeometryData()'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::default_instance()'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::SerializeWithCachedSizesToArray(unsigned char*) const'
build/libmessages_robocup_ssl_wrapper.pb.so: undefined reference to `SSL_GeometryData::MergePartialFromCodedStream(google::protobuf::io::CodedInputStream*)'
collect2: ld returned 1 exit status
make[2]: ** [clientTest] Erro 1
make[1]: ** [CMakeFiles/clientTest.dir/all] Erro 2
make: ** [all] Erro 2

一段时间以来我一直在尝试解决这个问题。 为什么是libmessages_robocup_ssl_wrapper.pb.so如果在链接之前已经构建，则显示错误？

这很可能是链接顺序。

看起来像messages_robocup_ssl_wrapper.pb依赖于取决于messages_robocup_ssl_geometry.pb。如果是这样，包装应该来before连接线中的几何形状。

target_link_libraries( clientTest robocup_ssl_client
                       messages_robocup_ssl_detection.pb
                       messages_robocup_ssl_wrapper.pb
                       messages_robocup_ssl_geometry.pb
                       messages_robocup_ssl_refbox_log.pb
                       netraw
                       robocup_ssl_client
                       protobuf
                       QtCore )

更好的是，让 CMake 来处理这样的依赖关系。

如果你添加...

target_link_libraries( messages_robocup_ssl_wrapper.pb
                       messages_robocup_ssl_geometry.pb )

那么 CMake 将自动保留该依赖关系messages_robocup_ssl_wrapper.pb被指定为另一个目标的依赖项。如果您这样做，那么您可以选择省略messages_robocup_ssl_geometry.pb来自target_link_libraries( clientTest ... ) call.