MyFitnessPal is one of the most popular trackers for food (it breaks down to calories, carbs, protein etc.). It is easy to use with loads of popular meals stored in it's memory (I haven't checked the dietary values - but they give it a tick if it's been verified by them). It also integrates with other health apps (such as Map My Run), adding more data to help with dose adjustment and daily decisions making.
MyFitnessPal is a very useful phone app and web site for not only checking the values of carbohydrates and other macronutrients in food, but for tracking the food you eat and the exercise you do. It can be useful for tracking what you really eat, as opposed to what you think you eat, and as such can be useful as part of any diet regime or way of eating. Beware that not all of the values are accurate though and many foods are missing. The phone app has a handy barcode scanner which works really well in practice and saves manual searching.