在 MacOS 上 C++编译链接的一个问题 - V2EX
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rainboat
V2EX    程序员

在 MacOS 上 C++编译链接的一个问题

  •  
  •   rainboat 2023-07-03 11:20:45 +08:00 1295 次点击
    这是一个创建于 838 天前的主题,其中的信息可能已经有所发展或是发生改变。

    使用 gflags 库,编译不通过

    最近项目里面要用 gflags 库,然后通过brew install gflags安装 gflags ,但是一通折腾就是编译不通过,不知道大伙有没有见过这样的问题,下面是编译不通过的代码

    编译不通过的代码

    #include <gflags/gflags.h> #include <iostream> DECLARE_string(test); int main(int argc, char* argv[]) { std::cout << FLAGS_test << std::endl; return 0; } 

    编译错误

    Undefined symbols for architecture x86_64: "fLS::FLAGS_test", referenced from: _main in test-d79d53.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation) 

    已经尝试过的编译命令

    下面是我尝试过的几个不同的编译命令,均无效:

    g++ test.cpp -lgflags g++ test.cpp /usr/local/lib/libgflags.dylib g++ -L /usr/local/Cellar/gflags/2.2.2/lib -lgflags test.cpp 

    目前分析了一下,通过通过brew install gflags安装的 gflags ,只提供了 dylib 动态链接库,如下所示:

    [/usr/local/Cellar/gflags/2.2.2/lib]$ ls cmake libgflags.2.2.dylib libgflags_nothreads.2.2.2.dylib libgflags_nothreads.dylib libgflags.2.2.2.dylib libgflags.dylib libgflags_nothreads.2.2.dylib pkgconfig [/usr/local/lib]$ ls | grep gflags libgflags.2.2.2.dylib libgflags.2.2.dylib libgflags.dylib libgflags_nothreads.2.2.2.dylib libgflags_nothreads.2.2.dylib libgflags_nothreads.dylib 

    是否使用动态链接库需要指定某些额外的选项,大家有类似的经验吗?

    7 条回复    2023-07-04 10:59:06 +08:00
    ingnoscemihi
        1
    ingnoscemihi  
       2023-07-03 11:59:07 +08:00
    brew link gflags
    clang++ test.cpp -o test
    ok 啦
    rainboat
        2
    rainboat  
    OP
       2023-07-03 12:05:43 +08:00
    @ingnoscemihi 执行 brew link gflags 提示我“Warning: Already linked”,再次编译还是同样的问题,难顶
    tangtang369
        3
    tangtang369  
       2023-07-03 15:29:12 +08:00
    ```
    #include <iostream>
    #include <gflags/gflags.h>

    //DECLARE_string(test);
    DEFINE_string(languages, "english,french,german","comma-separated list of languages to offer in the 'lang' menu");
    int main(int argc, char* argv[]) {
    std::cout << FLAGS_languages << std::endl;

    return 0;
    }
    ```
    用 DEFINE_string 可以编译通过
    rainboat
        4
    rainboat  
    OP
       2023-07-03 17:44:46 +08:00
    @tangtang369 还真是可以编译了,大佬牛
    rainboat
        5
    rainboat  
    OP
       2023-07-03 17:45:24 +08:00
    @tangtang369 不过好像运行 ./test --languages="chinese,japanese,korean",输出的结果还是 english,french,german ,这个命令行设置不起作用
    tangtang369
        6
    tangtang369  
       2023-07-04 10:03:58 +08:00   1
    @rainboat 要解析输入
    ```
    #include <iostream>
    #include <gflags/gflags.h>

    //DECLARE_string(test);
    DEFINE_string(languages, "english,french,german","comma-separated list of languages to offer in the 'lang' menu");
    int main(int argc, char* argv[]) {
    gflags::ParseCommandLineFlags(&argc, &argv, true);

    std::cout << FLAGS_languages << std::endl;

    return 0;
    }
    ```
    rainboat
        7
    rainboat  
    OP
       2023-07-04 10:59:06 +08:00
    @tangtang369 成功了,太感谢了,你真是我的哥!
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