Re: [isugamedev-devel] Overloading operators

[Kevin M. <ke...@vr...>]

operator*, +, -, etc... all need to return by value.  there is no other
way to do it - since returning ref to temporary is invalid.

you can optimize it though if it is inline by returning a constructor.
then the compiler will make one less temporary.


// slower
Vec3f Vec3f::operator-( const Vec3f& rhs )
{
   Vec3f temp;
   temp[0] =  vec[0] - rhs.vec[0];
   temp[1] =  vec[1] - rhs.vec[1];
   temp[2] =  vec[2] - rhs.vec[2];
   return temp;
}

// faster because of the return value optimization
Vec3f Vec3f::operator-( const Vec3f& rhs )
{
   return Vec3f( vec[0] - rhs.vec[0], vec[1] - rhs.vec[1], vec[2] - rhs.vec[2] );
}


of course, -= is the fastest since it does it by reference:

// fastest
Vec3f& Vec3f::operator-=( const Vec3f& rhs )
{
   vec[0] -=  rhs.vec[0];
   vec[1] -=  rhs.vec[1];
   vec[2] -=  rhs.vec[2];
   return *this;
}

if you want to see an example, or just use a math lib that has already
been built see the isugamedev/lib/math directory in CVS.  It has Vec2,
Vec3, Vec4, Matrix, Quat, and some others...


kevin


@--@---@---@----@-----@------@------@-----@----@---@---@--@
Kevin Meinert                                  __  _   __  
http://www.vrac.iastate.edu/~kevn         \  ||  \| \ /  ` 
Virtual Reality Applications Center        \ ||.-'|--\    
Howe Hall, Iowa State University, Ames Iowa \||  \|   \`__,
-----------------------------------------------------------

On Wed, 13 Feb 2002, Andres Reinot wrote:

> We're trying to re-make my vector library, right this time, with overloaded functions.  Now when I'm returning, I want to return a reference right? so that I can chain my addition/subtraction etc.?  But now for some functions I don't actually want to change the values of *this, I want to return a temporary vector I created in the operator+() function for example.  Can I return temp as a reference without problems of it going out of scope? What's the best way of doing what I'm trying to do?
>