如何针对依赖于另一个库的库 link 应用程序？

Question

我写了一个使用第 3 方共享库的共享库 mylib1，在我的例子中 libtinyxml2（对于这个问题，第 3 方库是无关紧要的：它可以是任何库） .我写了一个应用程序 app1 依赖于 mylib1.

构建 mylib1 成功，但构建 app1 失败，大概是因为 linker 没有被告知 link 反对 libtinyxml2 当 [=56] =]ing app1.

我错过了什么？

[I][~/Programs/cmake-jenkins/big_proj/src/build]$ make
[ 25%] Building CXX object mylib1/CMakeFiles/mylib1.dir/src/my_functions.cpp.o
[ 50%] Linking CXX shared library libmylib1.so
[ 50%] Built target mylib1
[ 75%] Building CXX object app1/CMakeFiles/app1.dir/src/main.cpp.o
[100%] Linking CXX executable app1
../mylib1/libmylib1.so: undefined reference to `tinyxml2::StrPair::Reset()'
../mylib1/libmylib1.so: undefined reference to `tinyxml2::StrPair::~StrPair()'
collect2: error: ld returned 1 exit status
make[2]: *** [app1/CMakeFiles/app1.dir/build.make:97: app1/app1] Error 1
make[1]: *** [CMakeFiles/Makefile2:402: app1/CMakeFiles/app1.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

文件夹结构

.
├── app1
│   ├── CMakeLists.txt
│   ├── src
│   │   ├── include
│   │   │   └── functions_p.hpp
│   │   └── main.cpp
├── CMakeLists.txt
└── mylib1
    ├── CMakeLists.txt
    ├── src
    │   ├── include
    │   │   └── my_functions.hpp
    │   └── my_functions.cpp

./CMakeLists.txt

# Top level CMakeLists.txt
cmake_minimum_required(VERSION 3.8.2)

add_subdirectory(app1)
add_subdirectory(mylib1)

app1/CMakeLists.txt

project("app1" CXX)

set(APP1_SOURCE_FILES src/main.cpp )
add_executable(app1 ${APP1_SOURCE_FILES})

target_include_directories(app1
    PRIVATE src/include)
target_link_libraries(app1 mylib1)

mylib1/CMakeLists.txt

project("lib1" CXX)

find_library(TINYXML_LIB tinyxml2 REQUIRED)

set(MYLIB1_SOURCE_FILES src/my_functions.cpp )
set(MYLIB_INCLUDE_FILES src/include/my_functions.hpp)
add_library(mylib1 SHARED ${MYLIB1_SOURCE_FILES} ${MYLIB1_INCLUDE_FILES} )

target_include_directories(mylib1
    PUBLIC src/include)
# I have checked that TINYXML_LIB is set, so the library IS found.
target_link_libraries(mylib1 PUBLIC ${TINYXML_LIB})

readelf 输出显示该库依赖于 libtinyxml2.so.6，并且此文件在我的系统上作为 /usr/lib/libtinyxml2.so.6 存在。

[I][~/Programs/cmake-jenkins/big_proj/src/build]$ readelf -d mylib1/libmylib1.so
Dynamic section at offset 0x16cd0 contains 29 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libtinyxml2.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libstdc++.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libgcc_s.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000000e (SONAME)             Library soname: [libmylib1.so]

运行在详细模式下生成的 Makefile 表明确实当 app1 被 linked 时，它不会 link 反对 libtinyxml2:

[ 75%] Linking CXX executable app1
cd /home/danb/Programs/cmake-jenkins/big_proj/src/build/app1 && /usr/bin/cmake -E cmake_link_script CMakeFiles/app1.dir/link.txt --verbose=1
/usr/bin/c++     CMakeFiles/app1.dir/src/main.cpp.o  -o app1 -Wl,-rpath,/home/danb/Programs/cmake-jenkins/big_proj/src/build/mylib1 ../mylib1/libmylib1.so

Answer 1

链接最终应用程序时会解析外部引用，因此在 target_link_libraries 中将 libtinyxml2 包含在 app1/CMakeLists.txt 中。

Answer 2

CMake 在模块中实现了这个特性。参见 CMake Modules 如果需要，模块会创建一个变量 FOOMODULE_LIBRARIES。此变量是

的列表

The libraries needed to use ...

因此您可以通过以下方式添加此依赖项：

为 mylib1 提供模块脚本
在项目 app1

示例：

find_package (mylib1)
include_directories(${mylib1_INCLUDE_DIRS})

add_executable(app1 main.cpp)
target_link_libraries(app1 ${mylib1_LIBRARIES})

注意：这使得 mylib1 独立于 app1。对于 mylib1 的任何更改，您必须做额外的工作来触发 app1 的构建。参见 CMake Tutorials at http://www.th-thielemann.de/development

Answer 3

tinyxml2 库或我的安装一定有问题（但它来自官方 ArchLinux 存储库），因为我用其他 2 个库替换了它，并且构建没有问题 app1.

我什至尝试手动 link app1，它仍然会给出相同的 undefined reference 错误：

/usr/bin/c++     CMakeFiles/app1.dir/src/main.cpp.o  -o app1 -Wl,-rpath,/home/danb/Programs/cmake-jenkins/big_proj/src/build/mylib1 ../mylib1/libmylib1.so -ltinyxml2 -L /usr/lib

我也试过用find_package()代替find_library()，因为libtinyxml2自带CMake模块，但问题依旧。

有趣的是我什至不使用tinyxml2::StrPair::Reset()。这就是库实现的全部内容：

#include <tinyxml2.h>

bool is_xml_empty() {
    tinyxml2::StrPair pair;
    char* a;
    char* b;
    pair.Set(a, b, 0);
    return pair.Empty();
}

还有！我可以构建一个依赖于 tinyxml2 的软件 (encfs)，并且构建得很好！这表明我的库安装没问题。

如何针对依赖于另一个库的库 link 应用程序？

How to link app against a library that depends on another library?

c++

linux

linker

cmake

shared-libraries

文件夹结构

./CMakeLists.txt

app1/CMakeLists.txt

mylib1/CMakeLists.txt