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本质上，我正在尝试使用redland rdf库，但我无法链接到它们。当我尝试使用 redland 库的简单基本程序时，出现以下错误： 

/usr/local/lib/librdf.a(rdf_init.o): In function `librdf_free_memory':
/home/ciaran/Software/redland/redland-1.0.17/src/rdf_init.c:671: undefined reference to `raptor_free_memory'
/usr/local/lib/librdf.a(rdf_init.o): In function `librdf_alloc_memory':
/home/ciaran/Software/redland/redland-1.0.17/src/rdf_init.c:689: undefined reference to `raptor_alloc_memory'
/usr/local/lib/librdf.a(rdf_init.o): In function `librdf_calloc_memory':
/home/ciaran/Software/redland/redland-1.0.17/src/rdf_init.c:707: undefined reference to `raptor_calloc_memory'

乍一看，您可能只是认为我缺少链接库，这是我在进一步检查之前的想法（见下文），但是，这些库都被考虑在内。

在这种情况下，一个适当的最小工作示例很困难，因为它需要获取和构建我正在尝试使用的库。但是，我创建了一个 GitHub存储库 

$ git clone git@github.com:CiaranWelsh/RedlandBuildTest.git

其中包含构建 Redland 库所需的源文件以及我正在使用的示例代码（中断）。

为了构建库，您还需要

    $ sudo apt install automake autoconf libtool gtk-doc-tools
    $ sudo apt install libxml2 libxml2-dev libxslt libxslt-dev libcurl4-openssl-dev libltdl-dev

请注意，我正在为 Linux 的 Windows 子系统开发 Ubuntu-18.04。

要获取、构建和安装库，我使用这些终端命令：

#raptor2
wget "http://download.librdf.org/source/raptor2-2.0.15.tar.gz" 
tar -xvf raptor2-2.0.15.tar.gz
cd raptor2-2.0.15
./autogen.sh 
make
sudo make install

# redland (librdf)
wget "http://download.librdf.org/source/redland-1.0.17.tar.gz" 
tar -xvf redland-1.0.17.tar.gz
cd redland-1.0.17 
./autogen.sh
make
sudo make install

# rasqal
wget "http://download.librdf.org/source/rasqal-0.9.33.tar.gz" 
tar -xvf rasqal-0.9.33.tar.gz
cd rasqal-0.9.33
./autogen.sh 
make 
sudo make install

它们在 github 存储库中作为 shell 脚本（get-raptor.sh和get-rasqal.sh）get-librdf.sh提供。

还有我最小的 CMake 脚本（也在存储库中）： 

cmake_minimum_required(VERSION 3.15)
project(RedlandBuildTest)

set(CMAKE_CXX_STANDARD 14)

find_library(RAPTOR2_STATIC_LIBRARY
        NAMES libraptor2.a
        PATHS /usr/local/lib
        )

find_path(RAPTOR2_INCLUDE_DIR
        NAMES raptor2.h
        PATHS /usr/local/include/raptor2
        )
find_library(RASQAL_STATIC_LIBRARY
        NAMES librasqal.a
        PATHS /usr/local/lib
        )

find_path(RASQAL_INCLUDE_DIR
        NAMES rasqal.h
        PATHS /usr/local/include/rasqal
        )

find_library(LIBRDF_STATIC_LIBRARY
        NAMES librdf.a
        PATHS /usr/local/lib
        )

find_path(LIBRDF_INCLUDE_DIR
        NAMES librdf.h
        PATHS /usr/local/include
        )

add_executable(RedlandBuildTest main.c)

target_include_directories(RedlandBuildTest PRIVATE
        ${RAPTOR2_INCLUDE_DIR}
        ${RASQAL_INCLUDE_DIR}
        ${LIBRDF_INCLUDE_DIR}
        )

target_link_libraries(RedlandBuildTest PRIVATE
        ${RAPTOR2_STATIC_LIBRARY}
        ${RASQAL_STATIC_LIBRARY}
        ${LIBRDF_STATIC_LIBRARY}
        curl
        xml2
        xslt
        ltdl
        )

get_target_property(LINK_LIBRARIES RedlandBuildTest LINK_LIBRARIES)
get_target_property(INCLUDE_DIRECTORIES RedlandBuildTest INCLUDE_DIRECTORIES)

message(STATUS "

LINK_LIBRARIES      ${LINK_LIBRARIES}
INCLUDE_DIRECTORIES ${INCLUDE_DIRECTORIES}

")

message(STATUS "

    RAPTOR2_STATIC_LIBRARY   ${RAPTOR2_STATIC_LIBRARY}
    RAPTOR2_INCLUDE_DIR      ${RAPTOR2_INCLUDE_DIR}

    RASQAL_STATIC_LIBRARY    ${RASQAL_STATIC_LIBRARY}
    RASQAL_INCLUDE_DIR       ${RASQAL_INCLUDE_DIR}

    LIBRDF_STATIC_LIBRARY    ${LIBRDF_STATIC_LIBRARY}
    LIBRDF_INCLUDE_DIR       ${LIBRDF_INCLUDE_DIR}

")

以及 CMake 命令的输出：

#(looks good)
LINK_LIBRARIES      /usr/local/lib/libraptor2.a;/usr/local/lib/librasqal.a;/usr/local/lib/librdf.a;curl;xml2;xslt;ltdl 
INCLUDE_DIRECTORIES /usr/local/include/raptor2;/usr/local/include/rasqal;/usr/local/include


    RAPTOR2_STATIC_LIBRARY   /usr/local/lib/libraptor2.a
    RAPTOR2_INCLUDE_DIR      /usr/local/include/raptor2

    RASQAL_STATIC_LIBRARY    /usr/local/lib/librasqal.a
    RASQAL_INCLUDE_DIR       /usr/local/include/rasqal

    LIBRDF_STATIC_LIBRARY    /usr/local/lib/librdf.a
    LIBRDF_INCLUDE_DIR       /usr/local/include

要构建，我正在使用 CLion，它只是在后台执行此操作：

mkdir build && cd build
CMake ..
make

因此给了我链接器错误。nm通过使用检查 Redland 库的内容，我进行了更深入的挖掘。

$nm -A librdf.a > librdf.a.nmoutput.txt
$nm -A libraptor2.a > libraptor2.a.nmoutput.txt
$nm -A librasqal.a > librasqal.a.nmoutput.txt

第一个违规undfined reference错误

/usr/local/lib/librdf.a(rdf_init.o): In function `librdf_free_memory':
/home/ciaran/Software/redland/redland-1.0.17/src/rdf_init.c:671: undefined reference to `raptor_free_memory'

is in function librdf_free_memory，这是内部定义的引用librdf.a 

# librdf.a.nmoutput.txt
...
librdf.a:rdf_init.o:0000000000000740 T librdf_free_memory
...

当我们查找对 的未定义引用时raptor_free_memory，我们发现它在内部确实是未定义的librdf.a.。

#librdf.a.nmoutput.txt
...
librdf.a:rdf_init.o:                 U raptor_free_memory
...

但这libraptor2.a无论如何都应该存在，如果我们看一下，我们会发现它确实存在并且定义为它应该是：

# libraptor2.a.nmoutput.txt
...
libraptor2.a:raptor_general.o:0000000000000863 T raptor_free_memory
...

我的理解是，链接的过程本质上应该用里面librdf.a的定义来填充里面的未定义引用libraptor.a，但这显然没有发生。

为什么会这样？

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1 回答 1

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当您的静态库相互依赖时，链接顺序很重要（请参阅此响应）。

如果librdf依赖于libraptor库（如链接错误所示），libraptor则应在指定给链接器时列出该 librdf库。target_link_libraries()根据您的库依赖关系，尝试重新排列命令中的库列表以遵守此顺序。

于 2020-03-26T15:25:25.777 回答