class - In function undefined reference c++

I get a strange error all the time.

/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crt1.o:

In function _start: >(.text+0x20): undefined reference to main
/tmp/cc4ZqKzy.o:

In function `Sep::Building::Building(Sep::Field::FieldType, >std::__cxx11::basic_string, >std::allocator >, char, bool, bool, unsigned int, unsigned int):

Building.cpp:(.text+0x3c): undefined reference to Sep::Field::Field()
collect2:

error: ld returned 1 exit status

I read a lot with this problem but none had the same. I included all the headers and also added ifndef guards.

main.cpp:

#include "Field.h"
#include "Building.h"

namespace Sep
{
  just some returns...
}


int main(int argc, char *argv[])
{
  Sep::Building Haus(Sep::Field::FieldType::HOME,"HOME", 'H', true, true, 100, 100);
  std::cout << "HAUS ABREV:" << Haus.getAbbrevationOnField() << '\n';
}

Field.h

#include 

#include 
#include 
#include 


#ifndef FIELD_H
#define FIELD_H

namespace Sep
{


  //----------------------------------------------------------------------------
  // Field class, containing all needed information to create a Field object
  //
  class Field
  {
    public :
      enum FieldType \
      {GRASS, WATER, OBSTACLE, STREET, HOME, MARKET, CLINIC, TOWNHALL};


    private:
      FieldType type_;
      std::string name_;
      char abbrevation_;
      bool buildable_;
      bool destroyable_;
      unsigned int build_cost_;
      unsigned int destroy_cost_;

    public:

      //------------------------------------------------------------------------
      // Field constructors & destructor
      //
      Field();
      Field(FieldType type);
      ~Field() noexcept;
      //------------------------------------------------------------------------
      //getters
      //
      Field::FieldType getFieldType() const { return type_; };

      const char getAbbrevationOnField() const { return abbrevation_; };

  //------------------------------------------------------------------------
  //setters
  //
      static std::string getName(FieldType type);
      FieldType getType() const;//steht oben in getFiel3dType Z55

      void setType(FieldType type){type_ = type;};
      void setName(std::string name){name_ = name;};

      void setAbbrevation(char abbrev){abbrevation_ = abbrev;};
      void setBuildable(bool buildable){buildable_ = buildable;};
      void setDestroyable(bool destroyable){destroyable_ = destroyable;};
      void setBuildCost(int b_cost){build_cost_ = b_cost;};
      void setDestroyCost(int d_cost){destroy_cost_ = d_cost;};
  };
}

#endif //FIELD.H

Field.cpp

#include "Field.h"
#include 
#include 
#include 
#include 

using Sep::Field;



//------------------------------------------------------------------------------
// Setter of the private FieldType type_ to the given param
//
// @param the type of field to get set
//
Field::Field(FieldType type)
{
  type_ = type;

};

Field::~Field(){};

//------------------------------------------------------------------------------
// Checks the type of a given field, returns the name of type as string
//
// @param type, the type of the field to check
//
// @return string the name of the type of the checked field

//
std::string Field::getName(FieldType type)
{
  switch (type)
  {
    case GRASS:
      return std::string("Grass");
    case WATER:
      return std::string("Water");
    case OBSTACLE:

      return std::string("Obstacle");
    case STREET:
      return std::string("Street");
    case HOME:
      return std::string("Home");
    case MARKET:
      return std::string("Market");
    case CLINIC:
      return std::string("Clinic");
    case TOWNHALL:

      return std::string("Town Hall");
    default:
      return std::string("Unknown Field");
  }
};

//------------------------------------------------------------------------------
// getters
//
// Getter from the private FieldType type_

//
// @param none
//
// @return the type of type_ as FieldType
//
Field::FieldType Field::getType() const
{
  return type_;
};

Building.h

#ifndef BUILDING_H
#define BUILDING_H

#include "Field.h"

namespace Sep
{

  class Building : public Field
  {
    private:

    public:
    Building(FieldType type, const std::string name, const char abbrevation, \
           const bool buildable, const bool destroyable,\
           const unsigned int b_cost, const unsigned int d_cost);
    ~Building();
  };

}

#endif //BUILDING_H

Building.cpp

#include "Building.h"
#include "Field.h"


Sep::Building::Building(FieldType type, const std::string name, \
         const char abbrevation, \
         const bool buildable, const bool destroyable,\
         const unsigned int b_cost, const unsigned int d_cost)
{
  Sep::Field::setType(type);
  Sep::Field::setName(name);
  Sep::Field::setAbbrevation(abbrevation);
  Sep::Field::setBuildable(buildable);
  Sep::Field::setDestroyable(destroyable);

  Sep::Field::setBuildCost(b_cost);
  Sep::Field::setDestroyCost(d_cost);
};

Sep::Building::~Building(){};

Has anyone a idea? Cause I get this error often in this project but in other classes.
The strange thing is that it seems like, that the program compiles correctly but on the start I get this collect2: error: ld returned 1 exit status.

Thx

Answer

Field.cpp need to be changed, if don't want to used Field() constructor just put the definition of Field() constructor empty.

For examples:
Field.cpp

#include "Field.h"
#include 
#include 

#include 
#include 

using Sep::Field;


//------------------------------------------------------------------------------
// Setter of the private FieldType type_ to the given param
//
// @param the type of field to get set

//
Field::Field(){ 

       //empty constructor or can initialize type_ to default value.
   }


Field::Field(FieldType type)
{
  type_ = type;

};

Field::~Field(){};

//------------------------------------------------------------------------------
// Checks the type of a given field, returns the name of type as string
//
// @param type, the type of the field to check
//
// @return string the name of the type of the checked field

//
std::string Field::getName(FieldType type)
{
  switch (type)
  {
    case GRASS:
      return std::string("Grass");
    case WATER:
      return std::string("Water");
    case OBSTACLE:

      return std::string("Obstacle");
    case STREET:
      return std::string("Street");
    case HOME:
      return std::string("Home");
    case MARKET:
      return std::string("Market");
    case CLINIC:
      return std::string("Clinic");
    case TOWNHALL:

      return std::string("Town Hall");
    default:
      return std::string("Unknown Field");
  }
};

//------------------------------------------------------------------------------
// getters
//
// Getter from the private FieldType type_

//
// @param none
//
// @return the type of type_ as FieldType
//
Field::FieldType Field::getType() const
{
  return type_;
};