CMake不适用于Google Protobuf [英] CMake doesn't work with Google Protobuf

问题描述

无法使用CMake链接protobuf库。我的CMakeLists

  cmake_minimum_required（版本3.6）
项目（地址簿）
 
 set（ CMAKE_CXX_STANDARD 11）
设置（PROJECT_NAME地址簿）
 
 ADD_SUBDIRECTORY（原型）
 
 INCLUDE_DIRECTORIES（$ {CMAKE_CURRENT_BINARY_DIR}）
 ADD_EXECUTABLE（main main.cpp） 
 TARGET_LINK_LIBRARIES（主协议$ {PROTOBUF_LIBRARY}）
  

，在proto子目录中还有另一个CMakeLists .txt（以这种方式在github repo https://github.com/shaochuan/cmake中完成-protobuf-example ）

  INCLUDE（FindProtobuf）
 FIND_PACKAGE（需要Protobuf）
 INCLUDE_DIRECTORIES（$ {PROTOBUF_INCLUDE_DIR}）
 PROTOBUF_GENERATE_CPP（PROTO_SRC PROTO_HEADER message.proto）
 ADD_LIBRARY（proto $ {PROTO_HEADER} $ {PROTO_SRC}）
  $ p> 
 
 
但是我的IDE仍然输出很多行，例如
 
 
 CMakeFiles / main.dir / main.cpp.o：在函数 main'中：
 /home/camille/ClionProjects/protobuf/main.cpp:42：未定义的引用
到 google :: protobuf :: internal :: VerifyVersion（int，int，char const *）'
 /home/camille/ClionProjects/protobuf/main.cpp ：49：未定义引用
到 tutorial :: AddressBook :: AddressBook（）'
 /home/camille/ClionProjects/protobuf/main.cpp:54：未定义引用
到 google :: protobuf :: Message :: ParseFromIstream（std :: istream *）'
 
 
我的错误在哪里？我如何使它起作用？
解决方案
您的程序由于 $ {PROTOBUF_LIBRARY}而无法链接在顶层 CMakeLists.txt 的范围内为空。发生这种情况是因为调用 add_subdirectory 创建了一个子作用域，并且 Protobuf_XXX 变量由 find_package（需要Protobuf）仅在该子范围内。
 
 
 
一种解决此问题的好方法是在中添加以下内容proto / CMakeLists.txt ：
  target_link_libraries（proto INTERFACE $ {Protobuf_LIBRARIES}）
  
这指示链接到 proto 的目标也链接到 $ {Protobuf_LIBRARIES} 。现在，您可以在顶级 CMakeLists.txt 中简化 target_link_libraries ：
  target_link_libraries（地址簿原型）
  
旁注，您也可以使用例如
  target_link_libraries（$ {PROJECT_NAME} INTERFACE ...）
  
  $ {PROJECT_NAME} 解析为您在<$ c中设置的任何内容$ c> project（...）在该 CMakeLists.txt 文件中的语句。
 
 
 
最后，请注意，它链接到 Protobuf_LIBRARIES 而不是 PROTOBUF_LIBRARY 。  Protobuf_LIBRARIES 包括协议缓冲区库和从属Pthreads库。
 
Unable to link protobuf library using CMake. My CMakeLists is 
cmake_minimum_required(VERSION 3.6)
project(addressbook)

set(CMAKE_CXX_STANDARD 11)
set(PROJECT_NAME addressbook)

ADD_SUBDIRECTORY(proto)

INCLUDE_DIRECTORIES(${CMAKE_CURRENT_BINARY_DIR})
ADD_EXECUTABLE(main main.cpp)
TARGET_LINK_LIBRARIES(main proto ${PROTOBUF_LIBRARY})
and in proto subdirectory there is another CMakeLists.txt (that way it is done in github repo https://github.com/shaochuan/cmake-protobuf-example)
INCLUDE(FindProtobuf)
FIND_PACKAGE(Protobuf REQUIRED)
INCLUDE_DIRECTORIES(${PROTOBUF_INCLUDE_DIR})
PROTOBUF_GENERATE_CPP(PROTO_SRC PROTO_HEADER message.proto)
ADD_LIBRARY(proto ${PROTO_HEADER} ${PROTO_SRC})
But my IDE still outputs buch of lines like

  
CMakeFiles/main.dir/main.cpp.o: In function main':
  /home/camille/ClionProjects/protobuf/main.cpp:42: undefined reference
  togoogle::protobuf::internal::VerifyVersion(int, int, char const*)'
  /home/camille/ClionProjects/protobuf/main.cpp:49: undefined reference
  to tutorial::AddressBook::AddressBook()'
  /home/camille/ClionProjects/protobuf/main.cpp:54: undefined reference
  togoogle::protobuf::Message::ParseFromIstream(std::istream*)'
Where is my mistake? How do I make it work?
解决方案
Your program fails to link because ${PROTOBUF_LIBRARY} is empty in the scope of your top-level CMakeLists.txt. This happens because calling add_subdirectory creates a child scope, and the Protobuf_XXX variables set by find_package(Protobuf REQUIRED) are only in that child scope.

A good way to fix this is to add the following to proto/CMakeLists.txt:
target_link_libraries(proto INTERFACE ${Protobuf_LIBRARIES})
This instructs targets that link to proto to also link to ${Protobuf_LIBRARIES}. Now you can simplify target_link_libraries in your top-level CMakeLists.txt:
target_link_libraries(addressbook proto)
On a side note, you could also use e.g.
target_link_libraries(${PROJECT_NAME} INTERFACE ... )
${PROJECT_NAME} resolves to whatever you have set in the project(...) statement in that CMakeLists.txt file.

Finally, note that this links to Protobuf_LIBRARIES instead of PROTOBUF_LIBRARY. Protobuf_LIBRARIES includes both the Protocol Buffers libraries and the dependent Pthreads library.

                        
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