Circular dependency c++ fails with forward decleration -

i have 2 classes, meassurementiteration , meassurementset. meassurementiteration has vector of sets, , set has pointer iteration.

meassurementiteration

#pragma once #include <vector> #include "meassurementsetrepo.h" #include "meassurementset.h"       class meassurementiteration     {     public:          meassurementiteration(const int id, const long start, const long end, const bool active)             : id_(id)             , start_(start)             , end_(end)             , active_(active)         {}                meassurementiteration();         ~meassurementiteration() = default;          std::vector<meassurementset>& getmeasurementset()         {             /** magic **/             return this->mssets_;         }      private:         const int id_;         const long start_;         long end_;         bool active_;         meassurementsetrepo mssetrepo;         std::vector<meassurementset> mssets_;     }; 

meassurementset

#pragma once  #include <string> #include <memory> #include "meassurementiterationrepo.h"  class meassurementiteration;       class meassurementset     {      public:         meassurementset(const int id, const std::string & way, const int it_id)              : id_(id)             , msway_(way)             , meassurementiteration_id_(it_id)         {             msit_ = nullptr;         }          ~meassurementset()         {             delete msit_;         }          meassurementiteration& getmsiteration()         {              if (this->msit_ == nullptr)             {             /** magic sets msit **/             }             return *msit_;            }      private:         int id_;         const std::string msway_;         const int meassurementiteration_id_;         meassurementiterationrepo msitrepo_;         meassurementiteration * msit_;     }; 

i cannot understand why i'm getting circular dependency here. when read other posts, seems way it. can explain me, i'm doing wrong?

update: problem seems due use of opposite class'es repository. illustrate, see figure.

how can solve dependency-hell?

there 1 important principle learn, , interfacing.

the idea when want use 1 of classes, want know what class does. not need know how it, aka implementation details.

that 1 of reasons why c++ separates files header files , source files. header files should contain does, source files how it's done. 1 argue new format in header file contains nothing public declarations (that is, without private member variables, private helper methods etc.).

using cause. don't see problematic line in particular @ first glance, might iterationrepo includes iteration includes set includes iterationrepo.

how having interfaces you: in headers, declare only, not implement (some one-liners, recommend not doing either). forward-declare only. include in source files. can't have circular dependency way.

(the rule broken member variable types of course - if has member variable b, needs know b in order know it's size, therefore needs include in header.)