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?

It adds constructors and destructors that do nothing. If you want FUNCTIONAL constructors/destructors, you need to handle them yourself.

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.

"I have to use .h, thats why i do that."

Why? Doesn't this work on your compiler:

Code:

---

#include <iostream>
using namespace std;

int main ()
{
        cout<<"Hello world."<<endl;
       
        getchar();//To pause DOS window
        return 0;
}

---

Post the code and post the errors.

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

Code:

---

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

---

That's your problem right there. Should look like this:

Code:

---

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

---

Semicolon goes after the definition brackets. Now, you really should use an initializer list to initialize itsX and itsY, but that would just add to confusion...

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

Quote:

---

It shouldn't. You forgot to #include <cstdio>.

---

It does, and no, I didn't forget.

getchar( ) is defined in <cstdio>, not <iostream>.

Ok, i think i did this right, but it won't compile. Ill post the code and the compiler errors.

Code:

---

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

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

workingclass()
{
cout<<"stuff";
}
~workingclass()
{
}


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

---

And the errors i get....

Code:

---

12 C:\Documents and Settings\User\Desktop\main.cpp
parse error before `('

17 C:\Documents and Settings\User\Desktop\main.cpp
destructors must be member functions

 C:\Documents and Settings\User\Desktop\Makefile.win
[Build Error]  [main.o] Error 1

---

Almost there.

1)Don't use header files with .h extensions. Use the equivalent header names found here:

http://www.cplusplus.com/doc/ansi/hfiles.html

2)Add a using declaration after your includes, like

using namespace std;

3)For short functions you should just define them inside the class. If you do define a function outside the class, it must be qualified with the class name, so that the compiler knows what class the definition belongs to, like this:

Code:

---

workingclass::workingclass()
{
  cout<<"stuff";
}

---

Just add "workingclass::" in front of any function you define outside of your class. Also, if you had a function with a return type of int, this is what the format would look if you defined it outside the class:

Code:

---

int workingclass::my_function()
{
    .....
    return 50;
}

---

The return type goes all the way to the left.

4)Unless you're going to be using arguments entered on the command line(which I assume you aren't) use the following format for main():

Code:

---

int main()
{
  ....
  ....
  return 0;
}

---

It's much easier to type.

Quote:

---

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

---

You have to? Who says so? You are already using one non-h header (<iostream>), so you can use all others too.

When i delete off the .h, i get compiler errors. Does it really make a difference anyways?

Also, what excactly does "using namespace std;" or whatever it was, do?

Ok, update, scratch that compiler error stuff with the .h. I didnt know that it was written different in C++.