Skip to content
  • Categories
  • Recent
  • Tags
  • Popular
  • World
  • Users
  • Groups
Skins
  • Light
  • Cerulean
  • Cosmo
  • Flatly
  • Journal
  • Litera
  • Lumen
  • Lux
  • Materia
  • Minty
  • Morph
  • Pulse
  • Sandstone
  • Simplex
  • Sketchy
  • Spacelab
  • United
  • Yeti
  • Zephyr
  • Dark
  • Cyborg
  • Darkly
  • Quartz
  • Slate
  • Solar
  • Superhero
  • Vapor

  • Default (No Skin)
  • No Skin
Collapse
Code Project
  1. Home
  2. The Lounge
  3. Is main() a callback function?

Is main() a callback function?

Scheduled Pinned Locked Moved The Lounge
question
44 Posts 15 Posters 0 Views 1 Watching
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • H honey the codewitch

    C is for wimps Real programmers use butterflies

    Real programmers use butterflies

    T Offline
    T Offline
    TheGreatAndPowerfulOz
    wrote on last edited by
    #32

    Real programmers use galaxy-sized gravitic lenses.

    #SupportHeForShe Government can give you nothing but what it takes from somebody else. A government big enough to give you everything you want is big enough to take everything you've got, including your freedom.-Ezra Taft Benson You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun

    H 1 Reply Last reply
    0
    • K k5054

      raddevus wrote:

      * Cannot have its address taken. * Cannot be called.

      Lies. You can call main, and you can take its address. This compiles and runs in VS2019:

      #include int main(int argc, char **argv)
      {
      if(argc <= 1) {
      auto main_ptr{main};
      std::cout << "pointer to main = " << main_ptr << std::endl;
      std::cout << "exiting ..." << std::endl;
      return 0;
      }
      std::cout << "argc = " << argc << std::endl;
      main(--argc, argv);
      }

      Interestingly, in linux you auto main_ptr{main} is 1, but for windows it looks like an address: 0008151E Update: I should also point out that the instances where you might need to call main from within you program are vanishingly small. In general, if you think you need to, you're almost certainly wrong.

      P Offline
      P Offline
      PIEBALDconsult
      wrote on last edited by
      #33

      Hold my Jolt Cola...

      1 Reply Last reply
      0
      • T TheGreatAndPowerfulOz

        Real programmers use galaxy-sized gravitic lenses.

        #SupportHeForShe Government can give you nothing but what it takes from somebody else. A government big enough to give you everything you want is big enough to take everything you've got, including your freedom.-Ezra Taft Benson You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun

        H Offline
        H Offline
        honey the codewitch
        wrote on last edited by
        #34

        Focused using butterflies

        Real programmers use butterflies

        T 1 Reply Last reply
        0
        • D DRHuff

          Well it never called me back - and I thought we had such a connection... :(( :(( :mad: :(( :((

          I, for one, like Roman Numerals.

          T Offline
          T Offline
          TheGreatAndPowerfulOz
          wrote on last edited by
          #35

          Did you give it your number, baby? ;P

          #SupportHeForShe Government can give you nothing but what it takes from somebody else. A government big enough to give you everything you want is big enough to take everything you've got, including your freedom.-Ezra Taft Benson You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun

          1 Reply Last reply
          0
          • H honey the codewitch

            Focused using butterflies

            Real programmers use butterflies

            T Offline
            T Offline
            TheGreatAndPowerfulOz
            wrote on last edited by
            #36

            honey the codewitch wrote:

            Focused using butterflies

            that are manipulated using gravitic lenses

            #SupportHeForShe Government can give you nothing but what it takes from somebody else. A government big enough to give you everything you want is big enough to take everything you've got, including your freedom.-Ezra Taft Benson You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun

            H 1 Reply Last reply
            0
            • T TheGreatAndPowerfulOz

              honey the codewitch wrote:

              Focused using butterflies

              that are manipulated using gravitic lenses

              #SupportHeForShe Government can give you nothing but what it takes from somebody else. A government big enough to give you everything you want is big enough to take everything you've got, including your freedom.-Ezra Taft Benson You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun

              H Offline
              H Offline
              honey the codewitch
              wrote on last edited by
              #37

              created from the silk of butterfly cocoons :-D

              Real programmers use butterflies

              T 1 Reply Last reply
              0
              • OriginalGriffO OriginalGriff

                Difficult to tell, it was yelling a lot and slurring it's words.

                "I have no idea what I did, but I'm taking full credit for it." - ThisOldTony AntiTwitter: @DalekDave is now a follower!

                D Offline
                D Offline
                DRHuff
                wrote on last edited by
                #38

                So it was yaccing with a lisp?

                I, for one, like Roman Numerals.

                1 Reply Last reply
                0
                • R Rob Philpott

                  That reminds me of a thing I read some time back, titled something along the lines of 'the 50 things Windows does before hitting main()'. Can't find it but it's out there somewhere, by one of the SysInternals lot I think. It was both interesting and really boring at the same time.

                  Regards, Rob Philpott.

                  R Offline
                  R Offline
                  Rick York
                  wrote on last edited by
                  #39

                  If you have Visual Studio you can see what the C run-time library does by looking at its source. I was checking that out just today.

                  "They have a consciousness, they have a life, they have a soul! Damn you! Let the rabbits wear glasses! Save our brothers! Can I get an amen?"

                  1 Reply Last reply
                  0
                  • R Rick York

                    Actually things are a little different. In the Visual Studio source, VC/Tools/MSVC/**version**/crt/src/vcruntime/vcstartup_internal.h has the prototypes and the calls are in exe_common.inl. WinMain and main are two different calls along with their wide character versions.

                    "They have a consciousness, they have a life, they have a soul! Damn you! Let the rabbits wear glasses! Save our brothers! Can I get an amen?"

                    L Offline
                    L Offline
                    Lost User
                    wrote on last edited by
                    #40

                    I suspected this might be the case, but I have not had access to the source for a number of years.

                    R 1 Reply Last reply
                    0
                    • R Rob Philpott

                      I can't make up my mind.

                      Regards, Rob Philpott.

                      S Offline
                      S Offline
                      Stefan_Lang
                      wrote on last edited by
                      #41

                      Only if used as such, e. g. in this code:

                      #include

                      using namespace std;

                      static int call_countdown = 3;
                      typedef int (*MyCallbackFun)();
                      int foo(MyCallbackFun cb, int count)
                      {
                      static int foo_counter = 0;
                      ++foo_counter;
                      cout << "enter foo[" << foo_counter <<"]: " << count << endl;
                      int result = cb();
                      cout << "exit foo[" << foo_counter << "]: " << result << endl;
                      return result;
                      }
                      int bar()
                      {
                      static int bar_counter = 0;
                      ++bar_counter;
                      cout << "bar[" << bar_counter << "]" << endl;
                      return -1;
                      }
                      int main()
                      {
                      static int call_counter = 0;
                      ++call_counter;
                      cout << "enter main[" << call_counter << "]" << endl;

                      int result = 0;
                      if (call\_counter < 5)
                      {
                          result = (call\_counter>2)
                              ? foo(bar, call\_counter)
                              : foo(main, call\_counter);
                      }
                      cout << "exit main\[" << call\_counter << "\]: " << result << endl;
                      
                      return call\_counter;
                      

                      }

                      You can test it here: https://www.onlinegdb.com/online_c++_compiler[^] or trust me that the output is:

                      enter main[1]
                      enter foo[1]: 1
                      enter main[2]
                      enter foo[2]: 2
                      enter main[3]
                      enter foo[3]: 3
                      bar[1]
                      exit foo[3]: -1
                      exit main[3]: -1
                      exit foo[3]: 3
                      exit main[3]: 3
                      exit foo[3]: 3
                      exit main[3]: 3

                      The tricky bit about this is that by using main() as a callback function, you're also using it recursively, which complicates matters considerably: it's easy to mess up the code and get an endless recursion. (that's why I added counters and output in every function) It's doable, but definitiely not a good idea.

                      GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)

                      1 Reply Last reply
                      0
                      • H honey the codewitch

                        created from the silk of butterfly cocoons :-D

                        Real programmers use butterflies

                        T Offline
                        T Offline
                        TheGreatAndPowerfulOz
                        wrote on last edited by
                        #42

                        lol, you got me there.

                        #SupportHeForShe Government can give you nothing but what it takes from somebody else. A government big enough to give you everything you want is big enough to take everything you've got, including your freedom.-Ezra Taft Benson You must accept 1 of 2 basic premises: Either we are alone in the universe or we are not alone. Either way, the implications are staggering!-Wernher von Braun

                        1 Reply Last reply
                        0
                        • L Lost User

                          I suspected this might be the case, but I have not had access to the source for a number of years.

                          R Offline
                          R Offline
                          Rick York
                          wrote on last edited by
                          #43

                          There were only minor changes. For the most part, what you wrote is correct.

                          "They have a consciousness, they have a life, they have a soul! Damn you! Let the rabbits wear glasses! Save our brothers! Can I get an amen?"

                          1 Reply Last reply
                          0
                          • R Rob Philpott

                            I can't make up my mind.

                            Regards, Rob Philpott.

                            S Offline
                            S Offline
                            Slow Eddie
                            wrote on last edited by
                            #44

                            No. It's a state in the Northeast. :laugh:

                            Oh Well.....

                            1 Reply Last reply
                            0
                            Reply
                            • Reply as topic
                            Log in to reply
                            • Oldest to Newest
                            • Newest to Oldest
                            • Most Votes


                            • Login

                            • Don't have an account? Register

                            • Login or register to search.
                            • First post
                              Last post
                            0
                            • Categories
                            • Recent
                            • Tags
                            • Popular
                            • World
                            • Users
                            • Groups