Adding empty element to declared container without declaring type of element












13















When we use a complicated container in C++, like



std::vector<std::map<std::string, std::set<std::string>>> table;


The only way to add an empty map (which may represent a row or column) is to initialize a new element and push it back. For example with



table.push_back(std::map<std::string, std::set<std::string>>());


Is there any way to avoid redeclaring the type, and just adding the correct typed element?






c++ c++11







share|improve this question





























    13















    When we use a complicated container in C++, like



    std::vector<std::map<std::string, std::set<std::string>>> table;


    The only way to add an empty map (which may represent a row or column) is to initialize a new element and push it back. For example with



    table.push_back(std::map<std::string, std::set<std::string>>());


    Is there any way to avoid redeclaring the type, and just adding the correct typed element?






    c++ c++11







    share|improve this question



























      13












      13








      13








      When we use a complicated container in C++, like



      std::vector<std::map<std::string, std::set<std::string>>> table;


      The only way to add an empty map (which may represent a row or column) is to initialize a new element and push it back. For example with



      table.push_back(std::map<std::string, std::set<std::string>>());


      Is there any way to avoid redeclaring the type, and just adding the correct typed element?






      c++ c++11







      share|improve this question
















      When we use a complicated container in C++, like



      std::vector<std::map<std::string, std::set<std::string>>> table;


      The only way to add an empty map (which may represent a row or column) is to initialize a new element and push it back. For example with



      table.push_back(std::map<std::string, std::set<std::string>>());


      Is there any way to avoid redeclaring the type, and just adding the correct typed element?






      c++ c++11




      c++ c++11






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 23 hours ago









      Mohammad Usman

      21.4k124658




      21.4k124658










      asked yesterday









      VineetVineet

      354411




      354411
























          4 Answers
          4






          active

          oldest

          votes


















          33














          From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.



          table.emplace_back();





          share|improve this answer

































            24














            You can take advantage of copy-list-initialization (since C++11) and just write



            table.push_back({});





            share|improve this answer

































              10














              Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).






              share|improve this answer































                4














                Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.



                I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!



                 using PhilosopherNameType = std::string;
                
 using NeighboursType      = std::set<PhilosopherNameType>;
                
 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;
                

                
 std::vector<NeighbourMapType> table;
                
 table.push_back(NeighbourMapType());


                I mention this because you can likely still benefit from this in other places.






                share|improve this answer



















                • 1





                  agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

                  – sudo rm -rf slash
                  2 hours ago











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                4 Answers
                4






                active

                oldest

                votes








                4 Answers
                4






                active

                oldest

                votes









                active

                oldest

                votes






                active

                oldest

                votes









                33














                From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.



                table.emplace_back();





                share|improve this answer






























                  33














                  From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.



                  table.emplace_back();





                  share|improve this answer




























                    33












                    33








                    33







                    From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.



                    table.emplace_back();





                    share|improve this answer















                    From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.



                    table.emplace_back();






                    share|improve this answer














                    share|improve this answer



                    share|improve this answer








                    edited yesterday

























                    answered yesterday









                    VineetVineet

                    354411




                    354411

























                        24














                        You can take advantage of copy-list-initialization (since C++11) and just write



                        table.push_back({});





                        share|improve this answer






























                          24














                          You can take advantage of copy-list-initialization (since C++11) and just write



                          table.push_back({});





                          share|improve this answer




























                            24












                            24








                            24







                            You can take advantage of copy-list-initialization (since C++11) and just write



                            table.push_back({});





                            share|improve this answer















                            You can take advantage of copy-list-initialization (since C++11) and just write



                            table.push_back({});






                            share|improve this answer














                            share|improve this answer



                            share|improve this answer








                            edited yesterday

























                            answered yesterday









                            songyuanyaosongyuanyao

                            93.6k11182248




                            93.6k11182248























                                10














                                Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).






                                share|improve this answer




























                                  10














                                  Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).






                                  share|improve this answer


























                                    10












                                    10








                                    10







                                    Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).






                                    share|improve this answer













                                    Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).







                                    share|improve this answer












                                    share|improve this answer



                                    share|improve this answer










                                    answered yesterday









                                    65026502

                                    87.6k13115218




                                    87.6k13115218























                                        4














                                        Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.



                                        I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!



                                         using PhilosopherNameType = std::string;
                                        
 using NeighboursType      = std::set<PhilosopherNameType>;
                                        
 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;
                                        

                                        
 std::vector<NeighbourMapType> table;
                                        
 table.push_back(NeighbourMapType());


                                        I mention this because you can likely still benefit from this in other places.






                                        share|improve this answer



















                                        • 1





                                          agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

                                          – sudo rm -rf slash
                                          2 hours ago
















                                        4














                                        Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.



                                        I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!



                                         using PhilosopherNameType = std::string;
                                        
 using NeighboursType      = std::set<PhilosopherNameType>;
                                        
 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;
                                        

                                        
 std::vector<NeighbourMapType> table;
                                        
 table.push_back(NeighbourMapType());


                                        I mention this because you can likely still benefit from this in other places.






                                        share|improve this answer



















                                        • 1





                                          agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

                                          – sudo rm -rf slash
                                          2 hours ago














                                        4












                                        4








                                        4







                                        Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.



                                        I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!



                                         using PhilosopherNameType = std::string;
                                        
 using NeighboursType      = std::set<PhilosopherNameType>;
                                        
 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;
                                        

                                        
 std::vector<NeighbourMapType> table;
                                        
 table.push_back(NeighbourMapType());


                                        I mention this because you can likely still benefit from this in other places.






                                        share|improve this answer













                                        Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.



                                        I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!



                                         using PhilosopherNameType = std::string;
                                        
 using NeighboursType      = std::set<PhilosopherNameType>;
                                        
 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;
                                        

                                        
 std::vector<NeighbourMapType> table;
                                        
 table.push_back(NeighbourMapType());


                                        I mention this because you can likely still benefit from this in other places.







                                        share|improve this answer












                                        share|improve this answer



                                        share|improve this answer










                                        answered 17 hours ago









                                        Lightness Races in OrbitLightness Races in Orbit

                                        294k54477809




                                        294k54477809








                                        • 1





                                          agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

                                          – sudo rm -rf slash
                                          2 hours ago














                                        • 1





                                          agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

                                          – sudo rm -rf slash
                                          2 hours ago








                                        1




                                        1





                                        agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

                                        – sudo rm -rf slash
                                        2 hours ago





                                        agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

                                        – sudo rm -rf slash
                                        2 hours ago


















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