对 boost::system::generic_category() 的未定义引用，尽管库被提供给 g++

Question

我在这里缺少哪些链接器标志？

我尝试在 Ubuntu 18.04 LTS 上编译它，但它失败了，它在 Debian 9 docker 映像中工作：

#include <boost/dll.hpp>

// Trying to compile it with:
// g++ -o program -lboost_filesystem -ldl -lboost_system program.cpp

int main() {
  boost::dll::program_location();
  return 0;
}

我得到的错误是：

/tmp/ccKlWUUd.o: In function `__static_initialization_and_destruction_0(int, int)':
program.cpp:(.text+0x68): undefined reference to `boost::system::generic_category()'
program.cpp:(.text+0x74): undefined reference to `boost::system::generic_category()'
program.cpp:(.text+0x80): undefined reference to `boost::system::system_category()'
/tmp/ccKlWUUd.o: In function `boost::system::error_code::error_code()':
program.cpp:(.text._ZN5boost6system10error_codeC2Ev[_ZN5boost6system10error_codeC5Ev]+0x17): undefined reference to `boost::system::system_category()'
/tmp/ccKlWUUd.o: In function `boost::system::error_category::std_category::equivalent(int, std::error_condition const&) const':
program.cpp:(.text._ZNK5boost6system14error_category12std_category10equivalentEiRKSt15error_condition[_ZNK5boost6system14error_category12std_category10equivalentEiRKSt15error_condition]+0xb8): undefined reference to `boost::system::generic_category()'
program.cpp:(.text._ZNK5boost6system14error_category12std_category10equivalentEiRKSt15error_condition[_ZNK5boost6system14error_category12std_category10equivalentEiRKSt15error_condition]+0xf3): undefined reference to `boost::system::generic_category()'
/tmp/ccKlWUUd.o: In function `boost::system::error_category::std_category::equivalent(std::error_code const&, int) const':
program.cpp:(.text._ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei[_ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei]+0xb8): undefined reference to `boost::system::generic_category()'
program.cpp:(.text._ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei[_ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei]+0xf3): undefined reference to `boost::system::generic_category()'
program.cpp:(.text._ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei[_ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei]+0x1d2): undefined reference to `boost::system::generic_category()'
/tmp/ccKlWUUd.o: In function `boost::dll::detail::report_error(boost::system::error_code const&, char const*)':
program.cpp:(.text._ZN5boost3dll6detail12report_errorERKNS_6system10error_codeEPKc[_ZN5boost3dll6detail12report_errorERKNS_6system10error_codeEPKc]+0x2a): undefined reference to `dlerror'
/tmp/ccKlWUUd.o: In function `boost::filesystem::read_symlink(boost::filesystem::path const&, boost::system::error_code&)':
program.cpp:(.text._ZN5boost10filesystem12read_symlinkERKNS0_4pathERNS_6system10error_codeE[_ZN5boost10filesystem12read_symlinkERKNS0_4pathERNS_6system10error_codeE]+0x36): undefined reference to `boost::filesystem::detail::read_symlink(boost::filesystem::path const&, boost::system::error_code*)'
collect2: error: ld returned 1 exit status

这里的系统是：

gcc: 7.0.3
boost: 1.65.1
libc6: 2.73

Answer 1

您的构建命令顺序错误，顺序很重要。

GCC 从左到右读取，当它已经知道需要时从库中获取符号。正如您将 program.cpp 放在最后一样，在所有列出的库都已被识别和丢弃之前，您不会知道这一点。

把program.cpp放在首位，然后是它需要的库。

g++ -o program program.cpp -lboost_filesystem -ldl -lboost_system

是的，这有点奇怪。 （更奇怪的是它在 Debian 上工作！虽然显然只有一些“最近的”Linuxy 发行版默认 --as-needed 开启，这就是导致您看到的行为的原因，表明该行为不一定得到保证。也许 Debian 9 完全没有这样做。）

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更多信息：

• Why does the order in which libraries are linked sometimes cause errors in GCC?