About the GUI Framework

This example is based on the "MFCConsole" framework. Between that base and the FAQ-specific extensions, there are 1800 lines of generic framework code, neatly separated from the specific parts of each example based on it. You do not need to understand this framework to learn from the examples, but if you are interested, you can find information about the framework on the MFCConsole page.

The example framework has two main menu items: "Start Winsock Handler" (Ctrl-W), and a generic "Action" item (Ctrl-A). When you give the Start command, it calls DoWinsock() this is similar to the console programs' DoWinsock() mechanism. The main difference in the GUI version is that DoWinsock() doesn't call the network handling functions directly: it just creates the object that does the real work. Then you give the Action command to do whatever specific thing the example does.

The Unique Bits

All the following comparisons are against the Winsock API-based asynchronous I/O client. That phrase is a mouthful, so we'll just call it the "pure asynch" client below.

The unique parts of this example are in the CCASClientSocket class. Aside from the CNetworkDriver interface, this class derives from CAsyncSocket so we can override functions like OnReceive(). I tried to derive from CWnd as well so we could have timeout timers like CAsyncClientWnd does, but that caused a multiple symbol problem that even virtual inheritance couldn't help. (VC++ bug?)

The Start() function in this example is much more substantial than in the pure async client, because it actually will initiate the connection to the server. That's because unlike my name lookup code, Microsoft's code in CAsyncSocket uses blocking DNS lookup functions. This makes the calling code simpler, but it does put your program at the mercy of your DNS server's speed. Anyway, it means we don't have to put off attempting the connection until Winsock calls us back with a window message telling us that the DNS lookup succeeded.

The rest of the program is pretty much identical to the pure async client, because CAsyncClient (like the rest of MFC) maps pretty closely to the underlying API. Nevertheless, the several small savings of the wrapper class did add up: this program is only 230 lines of code, a savings of 100 lines over the pure API version. To be fair, though, adding on your own asynchronous lookup function and timeout timers would eat into that 100 line savings.

The Code

The project package (33 KB) is a complete Visual C++ 5.0 project. It includes everything you need to build the sample.

License

Note that this example program is released under a different license than the other example programs. It's a BSD-style license, which means you can do anything you want with the example so long as you don't sue me or my employer if it prints 500 pages of "Microsoft sux!" on your customer's high-speed laser printer.