Thread: Starting to get aggrivated with classes....

Code:

#include <iostream>
#include <stdlib.h>
#include <fstream.h>


class aclass
{
public:
aclass();
~aclass();
};

 
int main(int argc, char *argv[])
{

aclass theclass;
 
  
  system("PAUSE");	
  return 0;
}

Why wont this compile. I declare the constructor, then the destructor. Then try to call an instance of the class and i get a linker error. If i do not add the 2 functions it will compile.

add
using namespace std;

after the includes

The linker expects the constructor/destructor to be defined somewhere... You've only declared them in that code.

The compiler supplies a default constructor and a default destructor, so you don't need to declare and define either one if you want your code to compile--of course it won't do anything.

Also, don't use standard library header files with a .h extension. All standard library header files have an equivalent header file without the .h extension.

Finally, use the following format for main() unless you plan on using command line arguments(if you don't know what that means, just use the following format):

int main()
{

...

return 0;
}

Indeed... Either of the following two are valid (and for that matter, equivalent).

Code:

class aclass
{};

... and ...

class aclass
{
public:
aclass() {}
~aclass() {}
};

It will actually 'compile' fine the way you have it, but since you went ahead and declared those functions, it expects them to be defined somewhere (potentially in a different file), and its the job of the linker to make sure that every declaration matches a definition somewhere.

Ok, so basicly i don't have to worry about adding a constructor and destructor, because the compiler automaticly does that for me?

For now this is fine, but i want to learn to create my own constructors and destructors as well. Can someone give me some example code creating a class with just the constructor and destructor?

Code:

class aclass
{
public:

aclass(int x, int y); { itsX=x; itsY=y; }
~aclass(); {} //doesn't need to do anything...

private:

int itsX;
int itsY;

};

then in main you would create an object:

Code:

aclass num1(12,5);

setting itsX to 12 and itsY to 5...

No compilation problem, but...

#include <iostream>
#include <fstream.h>

Don't mix non-h and h. Use only non-h unless you have to use h.

#include <iostream>
#include <fstream>
#include <cstdlib>

I have to use .h, thats why i do that. Someone esle already told me that above.

jawib: I get like 12 errors when i try to compile that code.

>>Doesn't this work on your compiler?
It shouldn't. You forgot to #include <cstdio>.

oops hehe...usually i define my functions outside of the class...guess i confused myself