我从未见过的编译器错误有人可以帮助我理解它吗？

Question

Undefined symbols for architecture x86_64:
  "KeyValue::KeyValue()", referenced from:
      Mapper::map() in Mapper.o
  "KeyValueList::KeyValueList()", referenced from:
      QuickSort::group() in QuickSort.o
  "KeyValueList::~KeyValueList()", referenced from:
      QuickSort::group() in QuickSort.o
      std::vector<KeyValueList, std::allocator<KeyValueList> >::_M_insert_aux(__gnu_cxx::__normal_iterator<KeyValueList*, std::vector<KeyValueList, std::allocator<KeyValueList> > >, KeyValueList const&) in QuickSort.o
      void std::_Destroy<KeyValueList>(KeyValueList*) in QuickSort.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

There's no other error in my code, I have 1 warning saying:

Implicit conversion loses integer precision: 'unsigned long' to 'int'

which I don't think would cause a linking error... Could someone help me understand what this error is and how it may have happened?

I can provide some code if needed.

Answer 1

You're trying to link to some code that doesn't exist; or certainly not for x86_64. Where is KeyValue() defined ? - link to that.

You probably included the header file for KeyValue in Mapper and Quicksort but didn't add the source for the compiler to deal with.