无法链接mongocxx静态库：链接时出现未定义引用错误求助

已安装的相关库文件 #

执行以下命令查看系统中的库文件：

$ l /usr/local/lib/libmongoc* 
/usr/local/lib/libmongoc-1.0.so@    /usr/local/lib/libmongoc-1.0.so.0.0.0  /usr/local/lib/libmongocxx.so@       /usr/local/lib/libmongocxx.so._noabi@
/usr/local/lib/libmongoc-1.0.so.0@  /usr/local/lib/libmongoc-static-1.0.a  /usr/local/lib/libmongocxx.so.3.8.0  /usr/local/lib/libmongocxx-static.a
$ l /usr/local/lib/libbson*
/usr/local/lib/libbson-1.0.so@    /usr/local/lib/libbson-1.0.so.0.0.0  /usr/local/lib/libbsoncxx.so.3.8.0    /usr/local/lib/libbsoncxx-static.a
/usr/local/lib/libbson-1.0.so.0@  /usr/local/lib/libbsoncxx.so@        /usr/local/lib/libbsoncxx.so._noabi@  /usr/local/lib/libbson-static-1.0.a

出现的未定义引用错误 #

构建时抛出链接错误：

main.cpp:(.text.startup+0x5e): undefined reference to `mongocxx::v_noabi::instance::instance()'
/usr/bin/ld: main.cpp:(.text.startup+0x6d): undefined reference to `bsoncxx::v_noabi::builder::core::core(bool)'
/usr/bin/ld: main.cpp:(.text.startup+0x91): undefined reference to `bsoncxx::v_noabi::builder::core::key_view(core::v1::basic_string_view<char, std::char_traits<char> >)'
/usr/bin/ld: main.cpp:(.text.startup+0xb5): undefined reference to `bsoncxx::v_noabi::builder::core::append(bsoncxx::v_noabi::types::b_string const&)'
/usr/bin/ld: main.cpp:(.text.startup+0xc2): undefined reference to `bsoncxx::v_noabi::builder::core::extract_document()'
/usr/bin/ld: main.cpp:(.text.startup+0xca): undefined reference to `bsoncxx::v_noabi::builder::core::~core()'
/usr/bin/ld: main.cpp:(.text.startup+0xe8): undefined reference to `bsoncxx::v_noabi::builder::core::~core()'
/usr/bin/ld: main.cpp:(.text.startup+0xf2): undefined reference to `mongocxx::v_noabi::instance::~instance()'
/usr/bin/ld: main.cpp:(.text.startup+0x112): undefined reference to `mongocxx::v_noabi::instance::~instance()'

当前CMake配置 #

find_package配置 #

find_package(mongocxx REQUIRED)
find_package(bsoncxx REQUIRED)
find_package(mongoc-1.0 REQUIRED)
find_package(mongoc-1.0 REQUIRED)
find_package(bson-1.0 REQUIRED)

target_link_libraries配置 #

target_link_libraries(your_target
    INTERFACE mongo::mongocxx_static
    INTERFACE mongo::bsoncxx_static
    INTERFACE mongo::bson_static
    INTERFACE mongo::mongoc_static
)

问题排查与解决方法 #

1. 修正链接关键字的使用错误 #

INTERFACE关键字用于库目标向依赖它的其他目标传递链接依赖，而你构建的是可执行文件，应该改用PRIVATE或PUBLIC：

target_link_libraries(your_target
    PRIVATE
        mongo::mongocxx_static
        mongo::bsoncxx_static
        mongo::mongoc_static
        mongo::bson_static
)

2. 调整静态库的链接顺序 #

静态链接对库的顺序敏感，依赖库必须放在被依赖库的后方。mongocxx依赖bsoncxx，而两者又依赖底层的mongoc和bson库，同时还要手动链接mongoc依赖的系统库（如线程库、SSL库），建议调整为：

target_link_libraries(your_target
    PRIVATE
        mongo::mongocxx_static
        mongo::bsoncxx_static
        mongo::mongoc_static
        mongo::bson_static
        pthread
        ssl
        crypto
)

3. 强制查找静态库 #

默认情况下find_package可能优先查找动态库，可在find_package前添加如下配置，强制CMake只查找静态库：

# 只查找.a后缀的静态库
set(CMAKE_FIND_LIBRARY_SUFFIXES ".a")

find_package(mongocxx REQUIRED CONFIG)
find_package(bsoncxx REQUIRED CONFIG)
find_package(mongoc-1.0 REQUIRED CONFIG)
find_package(bson-1.0 REQUIRED CONFIG)

4. 添加静态库编译宏 #

使用mongocxx静态库时，必须定义MONGOCXX_STATIC和BSONCXX_STATIC宏，否则会链接到动态库的符号：

target_compile_definitions(your_target PRIVATE MONGOCXX_STATIC BSONCXX_STATIC)

5. 清理重复的find_package调用 #

你的配置中重复调用了find_package(mongoc-1.0 REQUIRED)，可以删掉重复的一行，避免冗余。

内容的提问来源于stack exchange，提问作者user22343737