Question

I’m trying to wrap my head around exceptions and more I guess what they can do and even more important what they should and shouldn’t do.

So, I’ll go off with an example of how I am thinking at a pretty specific problem and hope that people will either bless or bash the ideas I’m having.

I’m reading settings off of a xml file, so I might have the settings but there is also the case where the specific setting might not be in there and that’d yield some troubles and a lot of “point-error-handling” or what to call it, of the type:
(observe: this is not “real code” but just some pseudo stuff hopefully making my point).

if (xml.attribute("some_attrib")) {
    settingForSomeAttrib = xml.attribute("some_attrib")->value();
} else {
    settingForSomeAttrib = "some default value";
}

So this will leave me with a check and an assignment more or less for every- and anything I’d like to do, which isn’t desirable.

Then I were thinking, perhaps I could run through it all, fetch anything which went wrong and hand it the default value, a bit of a just try to get it right and anything which didn’t work out we’ll handle afterwards..

Leading me to a try/catch type of thinking.

I am then thinking that perhaps I can do a try block:

try {
    setting1 = xml.attribute("attr1")->value(); // throws some kind of "attr1" exception?
    setting2 = xml.attribute("attr2")->value(); // -||-                "attr2" exception?
} catch (???) {
    //go through the things which went wrong and set them settings straight!
}

Hope that makes some kind of sense, or at least that it’s possible to follow my train of thought. I feel that it’s not really how exceptions are meant to be used.

I am thinking that my question is kind of two folded by this:

1) Is exceptions usable like this or is this just a bad idea?
2) how do people usually go about this in C++ to get code that aren’t all bloated in checking for validity?

Thanks.

Answer 1

I would certainly not use exceptions to handle settings that are merely optional.

Instead, I would do something along the following lines:

string getString(const XML& xml, const string& attrib, const string& defaultAttrib) {
  if (xml.attribute(attrib)) {
    return xml.attribute(attrib)->value();
  } else {
    return defaultAttrib;
  }
}

...
setting1 = getString(xml, "attrib1", "attrib1_default");
...