伯克利数据库：无法编译c++代码

Question

当我编译C++的示例代码时，我得到以下信息：

c++ excxx_example_database_read.cpp -o dbApp -I /usr/local/BerkeleyDB.5.0/include/
Undefined symbols:
  "Dbt::Dbt(void*, unsigned int)", referenced from:
      show_vendor(MyDb&, char const*)in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
  "Dbc::get(Dbt*, Dbt*, unsigned int)", referenced from:
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
  "Dbc::close()", referenced from:
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
  "Dbt::~Dbt()", referenced from:
      show_vendor(MyDb&, char const*)in ccnaWItX.o
      show_vendor(MyDb&, char const*)in ccnaWItX.o
      show_vendor(MyDb&, char const*)in ccnaWItX.o
      show_vendor(MyDb&, char const*)in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
  "Db::~Db()", referenced from:
      MyDb::~MyDb() in ccnaWItX.o
      MyDb::~MyDb() in ccnaWItX.o
  "typeinfo for DbException", referenced from:
      GCC_except_table3 in ccnaWItX.o
      GCC_except_table4 in ccnaWItX.o
      GCC_except_table5 in ccnaWItX.o
      GCC_except_table6 in ccnaWItX.o
      __ZTI11DbException$non_lazy_ptr in ccnaWItX.o
  "DbException::~DbException()", referenced from:
      __ZN11DbExceptionD1Ev$non_lazy_ptr in ccnaWItX.o
  "MyDb::close()", referenced from:
      MyDb::~MyDb() in ccnaWItX.o
  "MyDb::MyDb(std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, bool)", referenced from:
      _main in ccnaWItX.o
      _main in ccnaWItX.o
      _main in ccnaWItX.o
  "Dbt::Dbt()", referenced from:
      show_vendor(MyDb&, char const*)in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
  "DbException::get_errno() const", referenced from:
      show_vendor(MyDb&, char const*)in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
      _main in ccnaWItX.o
  "DbException::DbException(DbException const&)", referenced from:
      show_vendor(MyDb&, char const*)in ccnaWItX.o
      show_all_records(MyDb&, MyDb&) in ccnaWItX.o
      show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

我不知道问题是什么。请帮忙！

更新： 现在我使用：

getting_started baxxu$ c++ excxx_example_database_r
ead.cpp -o dbApp -I /usr/local/BerkeleyDB.5.0/include/ -L/usr/local/
BerkeleyDB.5.0/lib -ldb_cxx-5.0

仍然出现错误：

Undefined symbols:
  "MyDb::close()", referenced from:
      MyDb::~MyDb() in ccYCyhIg.o
  "MyDb::MyDb(std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, bool)", referenced from:
      _main in ccYCyhIg.o
      _main in ccYCyhIg.o
      _main in ccYCyhIg.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

Answer 1

您需要链接到 BerkeleyDB C++ 库。

c++ excxx_example_database_read.cpp -o dbApp -I /usr/local/BerkeleyDB.5.0/include/ -L/usr/local/BerkeleyDB.5.0/lib -ldb_cxx-5.0

（我假设这就是您已经安装了库并且版本基于包含（-I）指令。）

编辑：因此，看来您正在尝试编译发行版中包含的示例之一（excxx_example_database_read.cpp ）手工...它不仅仅是一个 .cpp 文件。 MyDB 对象不是 BerkeleyDB API 的一部分，而是如何从其子类化的示例。

cd 到 BerkeleyDB 源代码所在的位置，然后 cd build_unix 。到达那里后，执行 make excxx_example_database_read

Answer 2

这些是链接器错误 - 它们意味着您尚未链接构建此应用程序所需的一个或多个库。

该库的文档应该解释如何使用它构建应用程序。一般来说，您需要将库添加到编译器命令行：

c++ excxx_example_database_read.cpp -o dbApp -I /usr/local/BerkeleyDB.5.0/include/  -lsomething

将链接到在库搜索路径上找到的 libsomething.a。但要知道链接哪一个，您必须阅读文档。