Just a tip. Try screen scrap the page and dump it into a text file or just loop and compare it row by row. Google screen scraping using c++ or python or php. Should be easier. You don't have to do it manually. just trigger the program or dun it on schedule to screen scrap the web as and when you want it. Post again if you still can't find the way to do it. Screen scrap is reading the tags of the html

While you can totally do this in C++, it's much faster to do this in another language like Python for example. Google "parsing webpage python" and I'm sure you'll find results. You could do a python solution in probably under a day or two even if you don't know python but a C++ solution might take you a bit longer unless you use libraries that you're already familiar with...

Your question is all over the place.

You need to do this in steps.

What is step 1?

Do you already know how to do step 1?

You need to CLEARLY specify every step that you already know how to do, and then specify the next step and ask just about that one.

I want to set notifications to go off when the data goes below and above certain thresholds. I know how to do that, it the automatic reading of the correct field that I am interested. For example, see

http://waterdata.usgs.gov/or/nwis/current/?type=flow

I want an alarm to tell me when certain rivers go above a certain height and/or flow in Cubic Feet per Second. I set the thresholds in C, but how do I access that row associated with a given river? I can program which are which manually since I only need 20 or so rivers and the page's format doesn't change often so I can redo that once in awhile.

I know this isn't the easiest problem. I don[t expect a full solution unless also interested. Mainly I need the right search phrase and have no idea what this topic is called. Thanks a lot!