Undefined Reference to

Question

When I compile my code for a linked list  I get a bunch of undefined reference errors   The code is below   I have been compiling with both of these statements   g   test cpp    as well as   g   LinearNode h LinearNode cpp LinkedList h LinkedList cpp test cpp     I really do not understand why I am getting these errors because I am really rusty on classes in C     I could really use some help   LinearNode h    ifndef LINEARNODE H  define LINEARNODE H  include lt iostream gt   using namespace std   class LinearNode       public            Constructor for the LinearNode class that takes no arguments          LinearNode              Constructor for the LinearNode class that takes the element as an argument         LinearNode int el             returns the next node in the set          LinearNode  getNext              returns the previous node in the set         LinearNode  getPrevious              sets the next element in the set         void setNext LinearNode  node             sets the previous element in the set         void setPrevious LinearNode  node             sets the element of the node         void setElement int el             gets the element of the node         int getElement         private           LinearNode  next          LinearNode  previous          int element              ends the LinearNode class   endif   LinearNode cpp    ifndef LINEARNODE cpp  define LINEARNODE cpp  include lt iostream gt   include LinearNode h   using namespace std     Constructor for LinearNode  sets next and element to initialized states LinearNode  LinearNode         next   NULL      element   0     ends LinearNode default constructor    Constructor for LinearNode takes an element as argument  LinearNode  LinearNode int el        next   NULL      previous   NULL      element   0     ends LinearNode constructor    returns the next element in the structure LinearNode  LinearNode  getNext         return next     ends getNext function    returns previous element in structure LinearNode  LinearNode  getPrevious         return previous     ends getPrevious function    sets the next variable for the node void LinearNode  setNext LinearNode  node        next   node     ends the setNext function    sets previous for the node void LinearNode  setPrevious LinearNode  node        previous   node     ends the setPrevious function    returns element of the node int LinearNode  getElement         return element     ends the getelement function    sets the element of the node void LinearNode  setElement int el        element   el     ends the setElement function   endif   LinkedList h    ifndef LINKEDLIST H  define LINKEDLIST H  include lt iostream gt   include LinearNode h   using namespace std   class LinkedList       public          LinkedList            void add int element           int removie  int element        private          int count          LinearNode  contents      ends the class linked list   endif   LinkedList cpp    ifndef LINKEDLIST CPP  define LINKEDLIST CPP   include lt iostream gt   include LinearNode h   include LinkedList h   using namespace std     linkedlist constructor for an empty linked list LinkedList  LinkedList         count   0      contents   NULL     ends the constructor    adds an element to the front of the linked list void LinkedList  add int element        int found   0  current   0       while   found    0   amp  amp   current   count                  if  contents getElement      element              found   1          else                           contents   contents getNext                current               ends the else statement        ends the while loop      if  found    0                LinearNode node   new LinearNode element           node setNext contents           contents setPrevious node           count           ends the found    0 if statment    ends the add function    this function removes one element from the linked list  int LinearNode  remove int element        int found   0       if  count    0          cout  lt  lt   The list is empty   lt  lt  endl      else                if  contents getElement      element                        result   contents getElement                contents   contents getNext               ends the contents getElement      element         else                        previous   contents              current   contents getNext                for  int index   0     index  lt  count   amp  amp   found    0   index                    if  current getElement     element                      found   1                  else                                       previous   current                      current   current getNext                       ends the else statement               if  found    0                  cout  lt  lt   The element is not in the list   lt  lt  endl              else                               result   current getElement                    previous setNext current getNext                    ends else statement               ends the else stamtement          count--         ends the else statement of count    0     return result     ends the remove function   endif   test cpp    include lt iostream gt   include LinearNode h   include LinkedList h   using namespace std   int main          LinearNode node1  node2  node3  move      LinkedList list           node1 setElement 1       node2 setElement 2       node3 setElement 3

User · Answer

Try to remove the constructor and destructors  it s working for me

User · Answer

Another way to get this error is by accidentally writing the definition of something in an anonymous namespace   foo h   namespace foo       void bar        foo cc   namespace foo       namespace       wrong         void bar     cout  lt  lt   hello                other cc file    include  foo h   void baz         foo  bar

User · Answer

I was getting this error because my cpp files was not added in the CMakeLists txt file

User · Answer

g   test cpp LinearNode cpp LinkedList cpp -o test

User · Answer

I had this issue when I forgot to add the new  h  c file I created to the meson recipe so this is just a friendly reminder

User · Answer

Usually headers guards are for header files  i e    h   not for source files   i e    cpp     Include the necessary standard headers and namespaces in source files    LinearNode h    ifndef LINEARNODE H  define LINEARNODE H  class LinearNode                     endif   LinearNode cpp    include  LinearNode h   include  lt iostream gt  using namespace std     And now the definitions   LinkedList h    ifndef LINKEDLIST H  define LINKEDLIST H  class LinearNode     Forward Declaration class LinkedList                   endif   LinkedList cpp   include  LinearNode h   include  LinkedList h   include  lt iostream gt  using namespace std      Definitions   test cpp is source file is fine  Note that header files are never compiled  Assuming all the files are in a single folder -  g   LinearNode cpp LinkedList cpp test cpp -o exe out

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