提升错误消息[重复]答案

【问题标题】：Boost error message [duplicate]提升错误消息[重复]
【发布时间】：2013-12-18 13:47:03
【问题描述】：

我在尝试使用 boost 1.55 库编译某些代码时收到一条我不理解的错误消息。起初我有一个简单的程序试图分配一个共享内存对象。遇到一些错误，最后我决定复制并粘贴 boost 示例并编译它。得到同样的错误。示例代码：

#include <boost/interprocess/shared_memory_object.hpp>
#include <boost/interprocess/mapped_region.hpp>
#include <cstring>
#include <cstdlib>
#include <string>

int main(int argc, char *argv[])
{
   using namespace boost::interprocess;

   if(argc == 1){  //Parent process
      //Remove shared memory on construction and destruction
      struct shm_remove
      {
         shm_remove() { shared_memory_object::remove("MySharedMemory"); }
         ~shm_remove(){ shared_memory_object::remove("MySharedMemory"); }
      } remover;

      //Create a shared memory object.
      shared_memory_object shm (create_only, "MySharedMemory", read_write);

      //Set size
      shm.truncate(1000);

      //Map the whole shared memory in this process
      mapped_region region(shm, read_write);

      //Write all the memory to 1
      std::memset(region.get_address(), 1, region.get_size());

      //Launch child process
      std::string s(argv[0]); s += " child ";
      if(0 != std::system(s.c_str()))
         return 1;
   }
   else{
      //Open already created shared memory object.
      shared_memory_object shm (open_only, "MySharedMemory", read_only);

      //Map the whole shared memory in this process
      mapped_region region(shm, read_only);

      //Check that memory was initialized to 1
      char *mem = static_cast<char*>(region.get_address());
      for(std::size_t i = 0; i < region.get_size(); ++i)
         if(*mem++ != 1)
            return 1;   //Error checking memory
   }
   return 0;
}

当我编译它时，我得到的错误是：

g++  -D_REENTRANT -o loadfrags loadfrags.o -Lstdc++ -Wl,--rpath -Wl,/usr/local/lib
loadfrags.o: In function `boost::interprocess::shared_memory_object::priv_open_or_create(boost::interprocess::ipcdetail::create_enum_t, char const*, boost::interprocess::mode_t, boost::interprocess::permissions const&)':
loadfrags.cc:(.text._ZN5boost12interprocess20shared_memory_object19priv_open_or_createENS0_9ipcdetail13create_enum_tEPKcNS0_6mode_tERKNS0_11permissionsE[boost::interprocess::shared_memory_object::priv_open_or_create(boost::interprocess::ipcdetail::create_enum_t, char const*, boost::interprocess::mode_t, boost::interprocess::permissions const&)]+0x105): undefined reference to `shm_open'
loadfrags.cc:(.text._ZN5boost12interprocess20shared_memory_object19priv_open_or_createENS0_9ipcdetail13create_enum_tEPKcNS0_6mode_tERKNS0_11permissionsE[boost::interprocess::shared_memory_object::priv_open_or_create(boost::interprocess::ipcdetail::create_enum_t, char const*, boost::interprocess::mode_t, boost::interprocess::permissions const&)]+0x139): undefined reference to `shm_open'
loadfrags.cc:(.text._ZN5boost12interprocess20shared_memory_object19priv_open_or_createENS0_9ipcdetail13create_enum_tEPKcNS0_6mode_tERKNS0_11permissionsE[boost::interprocess::shared_memory_object::priv_open_or_create(boost::interprocess::ipcdetail::create_enum_t, char const*, boost::interprocess::mode_t, boost::interprocess::permissions const&)]+0x18e): undefined reference to `shm_open'
loadfrags.cc:(.text._ZN5boost12interprocess20shared_memory_object19priv_open_or_createENS0_9ipcdetail13create_enum_tEPKcNS0_6mode_tERKNS0_11permissionsE[boost::interprocess::shared_memory_object::priv_open_or_create(boost::interprocess::ipcdetail::create_enum_t, char const*, boost::interprocess::mode_t, boost::interprocess::permissions const&)]+0x1e7): undefined reference to `shm_open'
loadfrags.o: In function `boost::interprocess::shared_memory_object::remove(char const*)':
loadfrags.cc:(.text._ZN5boost12interprocess20shared_memory_object6removeEPKc[boost::interprocess::shared_memory_object::remove(char const*)]+0x42): undefined reference to `shm_unlink'
collect2: ld returned 1 exit status
make: *** [loadfrags] Error 1

据我所知，这些库已正确安装。我能够毫无问题地编译和运行匿名共享内存对象程序。我不是一个 C++ 程序员，无法快速确定这里出了什么问题。我的想法是我错过了某种#include。任何人都可以提供任何见解/帮助，我将不胜感激。

【问题讨论】：

@Praetorian 我查看了该问题，但没有应用任何回复（我已将 -Lrt 添加到链接行）。
-L和-l是有区别的，前者用于链接器搜索后者指定的库的目录
@Praetorian 谢谢。小写的“L”起到了作用。
请改进您的标题，以便将此问题与标题列表中的其他问题区分开来。

标签： c++ boost

【解决方案1】：

错误信息中有线索表明这是链接问题：

undefined reference to 表示链接时需要的符号不可用

和

ld returned 1 exit status 表明 ld（链接器）没有成功完成。

诀窍是当您看到undefined reference to <some symbol> 时，您需要找到提供该符号的库并将-l<libraryName> 添加到编译器选项中。如果库不在正常位置，您可能还需要添加-L<PathWhereLibraryCanBeFound>。

如 cmets 中所示和 C++ boost libraries shared_memory_object undefined reference to 'shm_open' 中所建议的那样，添加 -lrt 可以解决这种情况下的问题。

【讨论】：