[edit] Variable-Width Characters
Before UNICODE, there was an internationalization attempt that introduced character strings with variable-width characters. Some characters, such as the standard ASCII characters would be 1 byte long. Other characters, such as extended character sets, were two characters long. These types of character formats fell out of favor with the advent of UNICODE because they are harder to write and much harder to read. Windows does still maintain some functionality to deal with variable-width strings, but we won't discuss those here.
Unfortunately all advantages of using wide characters were lost because the number of characters needed quickly exceeded the 65,536 possible 16-bit values. Windows actually uses what is called UTF-16 to store characters, where a large number of characters actually take //two// words, these are called "surrogate pairs". This development is after much of the Windows API documentation was written and much of it is now obsolete. You should never treat string data as an "array of characters", instead always treat it as a null-terminated block. For instance always send the entire string to a function to draw it on the screen, do not attempt to draw each character. Any code that puts a square bracket after a LPSTR is wrong.
At the same time, variable-width character-based strings made a big comeback in the multi-platform standard called UTF-8, which is pretty much the same idea as UTF-16 except with 8-bit units. It's primary advantage is that there is no need for two api's, the 'a' and 'w' apis would have been the same if this was used, and since both are variable-sized, it has no disadvantage. Although most Windows programmers are unfamiliar with it, you may see increased references to using the non-UNICODE api.
-- from Windows Programming
