learning dragonfly or C...

Matthew Dillon dillon at apollo.backplane.com
Thu Nov 11 14:05:36 PST 2004

:>    This brings up an interesting ancillary issue in that you might also
:>    see a very experienced C programmer use a slightly different sort
:>    of construction, like this:
:>    struct vnode *vp;
:>    struct vnode *nvp;
:>    if ((error = ckpt_fhtovp(&vnh->vnh_fh, &nvp)) != 0)
:>	    return error;
:>    vp = nvp;
:>    /* nvp ignored, vp used from here on */
:>    Care to take a guess at why advanced C programmers use this construction
:>    instead of simply passing &vp ?
:>					-Matt
:well not knowing what vnh_fh or ckpt_fhtovp is, sets me back a bit, but
:I'll guess:
:...need more info... 
:is it a buffer to throw out illegal file handles inherited by NFS?
:// George

    Nope.  Ignore the actual function names and ignore the function of
    the code, its irrelevant.  Just focus on the question:  Why is
    &nvp being passed to a function and then vp assigned to nvp when
    one could simply pass &vp to the function and get rid of nvp entirely?

    Let me modify the example a little:

	struct fubar *blah;
	struct fubar *nblah;

	blah = nblah;

	blech = blah->this + blah->that - somefunction(blah);

	blah blah blah...

    Ok, so, the question is, why would an advanced C programmer every
    want to create a separate variable to pass the address to a function
    and then simply assign the result back to the first variable and never
    use the second variable again?

					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>

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