c++ - Create a struct instance only if conditions are met in its constructor -

i want create instance of struct if conditions inside constructors met. if conditions not met, want not create instance. not sure if possible, , if not alternate way of doing it?

class consumer {     struct samplestruct             {                 myclass     *   m_object;                  routingitem()                 {                     m_object            = null;                 }                 myclass(std::string name)                 {                         if (! objsetting()->getobj(name, m_object))//this function supposed populate m_object, if fails, dont want create instance                             return; //i dont want create object if getobj() returns false                               }             };    std::vector<samplestruct> m_arrsample;  void loadsettings(std::string name) {  samplestruct * ptrs;  samplestruct s(name);   //i tried following 2 lines did'nt work. looks returning struct constructor still creates instance ptrs = &s; if (!ptrs) return;  m_arrsample.push_back(s);//only insert in vector if samplestruct created   }     } 

either use exception (as stefano says), or factory function (as minicaptain says).

the 2 versions this:

#include <stdexcept> #include <memory>  struct exceptionstyle {     std::unique_ptr<int> m_object;      exceptionstyle(std::string const &name) {         if (name == "good")             m_object.reset( new int(42) );         else             throw std::runtime_error(name);     } }; void save(exceptionstyle*) {} // stick in vector or  class factorystyle {     std::unique_ptr<int> m_object;      factorystyle() : m_object(new int(42)) {}  public:     static std::unique_ptr<factorystyle> create(std::string const &name) {         std::unique_ptr<factorystyle> obj;         if (name == "good")             obj.reset( new factorystyle );         return obj;     } }; void save(std::unique_ptr<factorystyle>) {} // stick in vector or 

can used follows:

void loadsettings(std::string const &name) {      // use exception style     try {         exceptionstyle *es = new exceptionstyle(name);         // if reach here, created ok         save(es);     } catch (std::runtime_exception) {}      // use factory style     std::unique_ptr<factorystyle> fs = factorystyle::create(name);     if (fs) {         // if reach here, created ok         save(fs);     } } 

an exception only way transfer control out of constructor without constructing instance. so, alternative check condition first.