DevC ++编译器错误

Question

I am to write a test program that tests various operations on the class as designed in a previous problem; showing the definition of clockType overloading as member functions. I get the following error when I compile it using Dev C++ compiler.

The error reads:

[link error] undefined reference "WinMain@16'
Id returned 1 exit status

This is my code:

#include <iostream>

using namespace std;

class clockType
{
public:
      void setTime (int hours, int minutes, int seconds);
      void getTime (int& hours, int& minutes, int& seconds) const;     
      clockType operator++();
      bool operator==(const clockType& otherClock) const;
      bool operator!= (const clockType& otherClock) const;
      bool operator<=(const clockType& otherClock) const;
      bool operator<(const clockType& otherClock) const;
      bool operator>=(const clockType& otherClock) const;
      bool operator>(const clockType& otherClock) const;
      clockType ();
      clockType (int hours = 0, int minutes = 0, int seconds = 0);
private:
        int hr;
        int min;
        int sec;
};
clockType clockType::operator++()
{
          sec++;
          if (sec > 59)
          {
                  sec = 0;
                  min++;
                  if (min > 59)
                  {
                          min = 0;
                          hr++;
                          if (hr > 23)
                          hr = 0;
                  }
          }
          return *this;
}
bool clockType::operator==(const clockType& otherClock) const
{
     return (hr == otherClock.hr && min == otherClock.min && sec == otherClock.sec);
}
bool clockType::operator<=(const clockType& otherClock) const
{
     return ((hr < otherClock.hr) || (hr == otherClock.hr && min < otherClock.min) || (hr == otherClock.hr && min == otherClock.min && sec <= otherClock.sec));
}
bool clockType::operator!=(const clockType& otherClock) const
{
          return (hr != otherClock.hr || min != otherClock.min || sec != otherClock.sec);
}
bool clockType::operator<(const clockType& otherClock) const
{
     return ((hr < otherClock.hr) || (hr == otherClock.hr && min < otherClock.min) || (hr == otherClock.hr && min == otherClock.min && sec < otherClock.sec));
}
bool clockType::operator>=(const clockType& otherClock) const
{
     return ((hr > otherClock.hr) || (hr == otherClock.hr && min > otherClock.min) || (hr == otherClock.hr && min == otherClock.min && sec >= otherClock.sec));
}
bool clockType::operator>(const clockType& otherClock) const
{
     return ((hr > otherClock.hr) || (hr == otherClock.hr && min > otherClock.min) || (hr == otherClock.hr && min == otherClock.min && sec > otherClock.sec));
}

void clockType::setTime(int hours, int minutes, int seconds)
{
     if (0 <= hours && hours < 24)
     hr = hours;
     else
     hr = 0;
     if (0 <= minutes && minutes < 60)
     min = minutes;
     else
     min = 0;
     if (0 <= seconds && seconds < 60)
     sec = seconds;
     else
     sec = 0;
}
void clockType::getTime(int& hours, int& minutes, int& seconds)const
{
   hours = hr;
   minutes = min;
   seconds = sec;
}
clockType::clockType(int hours, int minutes, int seconds)
{
 setTime(hours, minutes, seconds);
}

Any help on this matter would be greatly appreciated. I am not real good at programming, and I just can't find out why I would be getting this type of error. I haven't on my other programs that I have written for class thus far.

Answer 1

You are missing the int main() function. A class doesn't really compile into a program by itself, you could compile it into a DLL , but not into a executable without the main function. More specifically, the program will compile, but the linker is complaining a it needs to have an entry point for the program.

If you put this at the bottom of your program: however this merely causes the undefined reference to go away.

int main(){
    return 0;
}

In order to actually test your program, you will need to run some tests, maybe something like this:

#include <iostream>

// your class code here.

int main(){
    Clocktype clock;
    clock.setTime(15, 42, 13);
    int h, m, s;
    clock.getTime(&h, &m, &s);
    std::cout << h << m << s << std::endl;
    return 0;
}

Answer 2

It is not a compiler but a linking error, it says that the linker is trying to find the main function (to provide the entry point for a Windows application).

The compilation itself does work well (the linking step works after the compilation is successful).

Answer 3

There absolutely is an IDE called Dev-C++ made by the company Bloodshed, I believe it is discontinued but still fairly compatible and favoured as it is free and easy to use with a nice interface.

As to the OP's question, you need to be sure you have an application entry point, in your project settings (I haven't used Dev-C++ in years so take a look around), you will find something saying application type, the options listed will be something like

Console Application
GUI Application or maybe Win32 Application
Static Library
Dynamic Library

These are all different types of applications and it looks like by default your program has the Win32 Application setting, in this case the linker is looking for WinMain however you have not provided one in your project, if you wish for a simple console application change the application type to that setting, which will require a simple main function, examples of the application entry point functions for both Win32 and Console are

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int iShow)
{
return 0;
}

Or for a simple Console Application

int main(int argc, char* argv[])
{
return 0;
}

These functions are where you need to plug in the rest of your application in order for it to do anything, without this entry point your application cannot even be properly compiled and linked.

An example of making your application actually use your class (without using any functions)

int main(int argc, char* argv[])
{
   clockType  myClockType;
   myClockType.setTime(12, 30, 45);

   return 0;
}