C++ / Can't access class members through the "." operator

lokee · 07-04-2004, 11:55 AM

Hi,
This is really weird... I've been looking at this problem from different angles, but still: no solution.
Here's an example code:

Code:

class lo {public: int o;};
lo li;
li.o = 15;

This gives me(g++):

Code:

error: syntax error before `.' token

The version of g++ is:
g++ (GCC) 3.3.3 20040217 (Gentoo Linux 3.3.3, propolice-3.3-7).

Thanks in advance.

Vookimedlo · 07-04-2004, 12:11 PM

Hi,
Of course you can not this compile. You are not allowed to initialize attribute o outside a function.

for example you should do this:

Code:

class lo {public: int o;};

int main(int argc, char **argv)
{
	lo li;
	li.o = 15;
	return 0;
}

or in constructor like this:

Code:

lo::lo():o(15){}

Try it.

--Michal

lokee · 07-04-2004, 12:58 PM

This is funny!

Of course it's inside a function: the main().
Sorry for not writing it, I taught it was unnecessary to mention that.

Keep cool.

luxitan · 07-04-2004, 01:14 PM

you are doing something wrong, that code compiles fine in my machine, put the whole code that gives the error.

The_Nerd · 07-04-2004, 02:55 PM

Since I am learning C++ could some one please tell me the advantage of doing:

Code:

lo::lo():o(15){}

over:

Code:

lo::lo(){this->o=15;}

Thanks in advance.

Btw, there is nothing wrong with your code, compiles fine. Did you name your source file with a .cpp extension?

luxitan · 07-04-2004, 05:00 PM

in the code you gave I don't think there is a difference, but if you have something like this:

Code:

class A
{
  int var;

public :

  A(int a)
  {
    var = a;
  }
};

class B
{
  
  A a;

public :

  B() : a(5)
  {

  }

};

int main()
{
  B b;
}

it only compiles in the first notation

dakensta · 07-05-2004, 04:58 AM

Nerd

The difference is mostly in efficiency. By calling the assignment operator your member object has already been constructed with its default ctor. This doesn't matter for built-ins but if your member, o, is a large class with a detailed construction process of its own, e.g. multiple memory allocations, you can end up performing these operations upto 3 times, depending on your assignment operator.

HTH

lokee · 07-05-2004, 12:06 PM

Ok thanks to everyone for trying to help me...
How simple:
There was a missing "{", stupid me!

(Was trying everything in the same file)

Best regards,