oops? not sure. operator overloading (possible) problem

**w00tw00tkab00t** · 02-07-2006

yeah.... can somebody take a quick look at the unfinished code below and let me know if i'm properly overloading the operators? thanks.

Code:

matrix matrix::operator + (matrix other) {
	int y, x;
	this->accesserror = false; other.accesserror = false;
	if ((this->getrows() == other.getrows()) && (this->getcols() == other.getcols())) {
		matrix temp(this->getrows(), this->getcols());
		for (y = 1; y <= this->getrows(); y++) {
			for (x = 1; x <= this->getcols(); x++) {
				temp.setelem(y, x, (this->at(y, x) + other.at(y, x)));
				if ((this->accesserror) || (other.accesserror) || (temp.accesserror)) { break; }
			}
			if ((this->accesserror) || (other.accesserror) || (temp.accesserror)) { break; }
		}
	} else {
		matrix temp(1, 1);
		temp.setelem(1, 1, 0);
		this->accesserror = true; other.accesserror = true;
	}
	return temp;
} /*Matrix addition; make sure to check fail() */

and

Code:

bool matrix::operator == (matrix other) {
	int y, x;
	this->accesserror = false; other.accesserror = false;
	/*Row and column check */
	if (!((this->getrows() == other.getrows()) && (this->getcols() == other.getcols()))) {
		return false;
	}
	else {
		for (y = 1; y <= this->getrows(); y++) {
			for (x = 1; x <= this->getcols(); x++) {
				if ((this->at(y, x) != other.at(y, x)) {
					return false;
				}
			}
		}
	}
}

**ChaosEngine** · 02-07-2006

in your op+ you return a variable (temp) that's gone out of scope and will not compile. I'd also consider throwing an exception instead of return a 'null' matrix with an errorbit. Even better would be to use a template for the matrix so adding different sizes won't compile.

Code:

matrix<2, 1> m1;
matrix<2, 5> m2;

matrix<> m3 = m1 + m2; /// arrgggh compiler error!

'better compile-time then run-time and better run-time then never'

it's pretty easy to add two incompatible matrices and not check accesserror.
it's also pretty tedious to do this each time

Code:

matrix m1, m2;
matrix m3 = m1 + m2;
if (m3.accesserror )
{
   // erm, do something useful
}

in your op== you need a return true at the end of the method.

**w00tw00tkab00t** · 02-07-2006

well i haven't learned templates (knew only C until last week) but umm... what do u mean out of scope?

**CornedBee** · 02-07-2006

That part was wrong. If the copy constructor works properly, there is nothing to worry about here.

A possible efficiency problem lies in your passing the argument by value. You should change it to const reference.

**w00tw00tkab00t** · 02-07-2006

huh?
i don't have a copy constructor......

what part was wrong?

**ChaosEngine** · 02-07-2006

Originally Posted by CornedBee

That part was wrong. If the copy constructor works properly, there is nothing to worry about here.

A possible efficiency problem lies in your passing the argument by value. You should change it to const reference.

you're right about the reference, but unless I'm completely stoned (and I don't think I am) he's returning a variable that's already gone out of scope

Code:

// edited for clarity
matrix matrix::operator + (matrix other) 
{
    if (someCondition)
    {
        matrix temp(this->getrows(), this->getcols());
        // some stuff
    } // temp out of scope here
    else
    {
         matrix temp(1, 1);
         // more stuff
    } // 2nd temp out of scope

    // where'd this come from?
    return temp;
}

I am not talking about return a copy of a local temporary (I know how copy ctors work :P ), I'm talking about a syntax error.

**w00tw00tkab00t** · 02-07-2006

?????????????????
so variables go out of scope after conditionals? bleh. i never knew that.... or didn't remember. probably the first

**ChaosEngine** · 02-07-2006

Originally Posted by w00tw00tkab00t

?????????????????
so variables go out of scope after conditionals? bleh. i never knew that.... or didn't remember. probably the first

the {} braces are c/c++'s scope delimiters. anything created within a matching set of {}'s is automatically cleaned up at the end of that set. (in C, local stack variables used to be called auto-vars).

so,

Code:

void func()
{
     int outer = 0;
     {
         int inner = 0;
     }// inner dies here
  
     inner = 2; // compile error!!

     if (outer)
     {
          int ifVar = 0;
     } // ifVar dies here

     ifVar = 2; // compile error!!

     while(true)
     {
          int loopVar = 0;
     } // guess what happens to loopVar here?

     loopVar = 2; // compile error!!

} // outer dies here

outer = 2; // compile error!!

**CornedBee** · 02-08-2006

Originally Posted by w00tw00tkab00t

?????????????????
so variables go out of scope after conditionals? bleh. i never knew that.... or didn't remember. probably the first

Sorry, you're right. Didn't read the function closely enough.

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