Question:
What is giving me a redefinition of CMenuItems class error in this code?
//cmenu.hclass CMenuItem { public: char title[81]; virtual void Do_Command(void)=0;};//*********************//CMDS.CPP Defines and initializes menu commands.#include #include #include "cmenu.h"class CMenuBell:public CMenuItem{ void Do_Command(void);};class CMenuSaying:public CMenuItem{ void Do_Command(void);};class CMenuAdd:public CMenuItem{ void Do_Command(void);};void CMenuBell::Do_Command(void){ putc(' 07',stdout); // " 07" rings a bell}void CMenuSaying::Do_Command(void){ puts("If you know the meaning of the universe,"); puts("Make the sound of one hand clapping.");}void CMenuAdd::Do_Command(void){ double x,y; printf("Enter a number: "); scanf("%lf",&x); printf("Enter a number: "); scanf("%lf",&y); printf("The total is %f.", x+y);}int num_commands;CMenuItem *commands[20];void Init_Commands(void) { commands[0] = new CMenuBell; strcpy(commands[0]->title, "Sound a bell."); commands[1] = new CMenuSaying; strcpy(commands[1]->title, "Print a message."); commands[2] = new CMenuAdd; strcpy(commands[2]->title, "Add two numbers."); num_commands=3;}//************************//Main.cpp#include #include "cmenu.h"#include "CMDS.cpp"extern int num_commands;extern CMenuItem *commands[];void main(void) { int i, sel; Init_Commands(); do { puts("
MENU:
"); for (i=0; ititle"); printf("
Enter a selection: "); scanf("%d", &sel); if (sel>0 && sel<=num_commands) commands[sel]->Do_Command(); } while (sel <= num_commands);}
Answer:
The problem is that you're #including the header "cmenu.h" twice:
//CMDS.CPP Defines and initializes menu commands. #include#include #include "cmenu.h" // first time //Main.cpp #include #include "cmenu.h" // second time #include "CMDS.cpp"
To avoid this, you should add #include guards in "cmenu.h". This will prevent the multiple definition problem:
#ifndef CMENU_H #define CMENU_H //cmenu.h class CMenuItem { public: char title[81]; virtual void Do_Command(void)=0; }; #endif
It's always a good idea to add #include guards to every header file you write.
