Any idea why build failed on cpp?

[EY Tsai]

g++ -o CppClinicClient -I./gen-cpp -I/usr/local/include/thrift 
-I/usr/include/boost/  -I./ -L/usr/local/lib -lthrift main/CppClinicClient.cpp 
gen-cpp/petclinic_constants.cpp gen-cpp/petclinic_types.cpp  
gen-cpp/PetClinic.cpp
/tmp/ccSEmUDT.o: In function 
`std::less<tc_petclinic::Specialty>::operator()(tc_petclinic::Specialty const&, 
tc_petclinic::Specialty const&) const':
petclinic_types.cpp:(.text._ZNKSt4lessIN12tc_petclinic9SpecialtyEEclERKS1_S4_[std::less<tc_petclinic::Specialty>::operator()(tc_petclinic::Specialty
 const&, tc_petclinic::Specialty const&) const]+0x14): undefined reference to 
`tc_petclinic::Specialty::operator<(tc_petclinic::Specialty const&) const'
/tmp/ccSEmUDT.o: In function 
`std::less<tc_petclinic::Visit>::operator()(tc_petclinic::Visit const&, 
tc_petclinic::Visit const&) const':
petclinic_types.cpp:(.text._ZNKSt4lessIN12tc_petclinic5VisitEEclERKS1_S4_[std::less<tc_petclinic::Visit>::operator()(tc_petclinic::Visit
 const&, tc_petclinic::Visit const&) const]+0x14): undefined reference to 
`tc_petclinic::Visit::operator<(tc_petclinic::Visit const&) const'
/tmp/ccSEmUDT.o: In function 
`std::less<tc_petclinic::Pet>::operator()(tc_petclinic::Pet const&, 
tc_petclinic::Pet const&) const':
petclinic_types.cpp:(.text._ZNKSt4lessIN12tc_petclinic3PetEEclERKS1_S4_[std::less<tc_petclinic::Pet>::operator()(tc_petclinic::Pet
 const&, tc_petclinic::Pet const&) const]+0x14): undefined reference to 
`tc_petclinic::Pet::operator<(tc_petclinic::Pet const&) const'
collect2: ld returned 1 exit status
make: *** [client] Error 1

petclinic.thrif:

struct PetType {
  1: i32 id,
  2: string name
}

struct Specialty {
  1: i32 id,
  2: string name
}

struct Vet {
  1: i32 id,
  2: string firstName,
  3: string lastName,
  4: set<Specialty>  specialties
}

struct Visit {
  1: i32 id,
  2: i64 date,
  3: string description,
  4: i32 petFK
}

struct Pet {
  1: i32 id,
  2: string name
  3: string birthDate,
  4: PetType type,
  5: set<Visit>  visits,
  6: i32 ownerFK,
  7: i32 typeFK
}

struct Owner {
  1: i32 id,
  2: string firstName,
  3: string lastName
  4: i32 account,
  5: string address,
  6: string city,
  7: string telephone,
  8: set<Pet>  pets
}

service PetClinic {
  void putPetType(1: PetType petType),
  PetType getPetType(1: i32 id),
  void putPet(1: Pet pet),
  Pet getPet(1: i32 id),
  void putVisit(1: Visit visit),
  Visit getVisit(1: i32 id),
  void putOwnerPets(1: i32 ownerId, 2: set<Pet>  pets),
  set<Pet>  getOwnerPets(1: i32 ownerId),
  void putPetVisits(1: i32 petId, 2: set<Visit>  visits),
  set<Visit>  getPetVisits(1: i32 petId),
  void putOwner(1: Owner owner),
  Owner getOwner(1: i32 id)
}

Thanks