This page shows how to create an Ice application with C++ using the Ice C++98 mapping.
On this page:
Compiling a Slice Definition for C++
The first step in creating our C++ application is to compile our Slice definition to generate C++ proxies and skeletons. You can compile the definition as follows:
slice2cpp compiler produces two C++ source files from this definition,
Printer.hheader file contains C++ type definitions that correspond to the Slice definitions for our
Printerinterface. This header file must be included in both the client and the server source code.
Printer.cppfile contains the source code for our
Printerinterface. The generated source contains type-specific run-time support for both clients and servers. For example, it contains code that marshals parameter data (the string passed to the
printStringoperation) on the client side and unmarshals that data on the server side.
Printer.cppfile must be compiled and linked into both client and server.
Writing and Compiling a Server in C++
The source code for the server takes only a few lines and is shown in full here:
Every Ice source file starts with an include directive for
Ice.h, which contains the definitions for the Ice run time. We also include
Printer.h, which was generated by the Slice compiler and contains the C++ definitions for our printer interface, and we import the contents of the
Demo namespaces for brevity in the code that follows:
Our server implements a single printer servant, of type
PrinterI. Looking at the generated code in
Printer.h, we find the following (tidied up a little to get rid of irrelevant detail):
Printer skeleton class definition is generated by the Slice compiler. (Note that the
printString method is pure virtual so the skeleton class cannot be instantiated.) Our servant class inherits from the skeleton class to provide an implementation of the pure virtual
printString method. (By convention, we use an
I-suffix to indicate that the class implements an interface.)
The implementation of the
printString method is trivial: it simply writes its string argument to
printString has a second parameter of type
Ice::Current. As you can see from the definition of
Printer::printString, the Slice compiler generates a default argument for this parameter, so we can leave it unused in our implementation. (We will examine the purpose of the
Ice::Current parameter later.)
What follows is the server main program. Note the general structure of the code:
The body of
main contains a try/catch block, and we start by creating an Ice Communicator holder on the stack.
argv to the
CommunicatorHolder because the server may have command-line arguments that are of interest to the run time; for this example, the server does not require any command-line arguments.
CommunicatorHolder is a a RAII-helper class, which creates and holds an
Ice::Communicator object. The primary purpose of this holder object is to call
destroy on the communicator when the holder goes out of scope.
Failure to call
destroy on the communicator before the program exits results in undefined behavior.
Next, we have the actual server code:
The code goes through the following steps:
- We create an object adapter by calling
operator->()). The arguments we pass are
"SimplePrinterAdapter"(which is the name of the adapter) and
"default -p 10000", which instructs the adapter to listen for incoming requests using the default transport protocol (TCP/IP) at port number 10000.
- At this point, the server-side run time is initialized and we create a servant for our
Printerinterface by instantiating a
- We inform the object adapter of the presence of a new servant by calling
addon the adapter; the arguments to
addare the servant we have just instantiated, plus an identifier. In this case, the string
"SimplePrinter"is the name of the Ice object. (If we had multiple printers, each would have a different name or, more correctly, a different object identity.)
- Next, we activate the adapter by calling its
activatemethod. (The adapter is initially created in a holding state; this is useful if we have many servants that share the same adapter and do not want requests to be processed until after all the servants have been instantiated.) The server starts to process incoming requests from clients as soon as the adapter is activated.
- Finally, we call
waitForShutdown. This call suspends the calling thread until the server is shut down. (For now, we will simply interrupt the server on the command line when we no longer need it, which terminates the server immediately.)
Assuming that we have the server code in a file called
Server.cpp, we can compile it as follows:
This compiles both our application code and the code that was generated by the Slice compiler. Depending on your platform, you may have to add additional include directives or other options to the compiler; please see the demo programs that ship with Ice for the details.
Finally, we need to link the server into an executable:
Again, depending on the platform, the actual list of libraries you need to link against may be longer. The demo programs that ship with Ice contain all the detail.
Writing and Compiling a Client in C++
The client code looks very similar to the server. Here it is in full:
Note that the overall code layout is the same as for the server: we include the headers for the Ice run time and the header generated by the Slice compiler, and we use the same
try block and
catch handlers to deal with errors.
The code in the
try block does the following:
- As for the server, we initialize the Ice run time by creating a
- The next step is to obtain a proxy for the remote printer. We create a proxy by calling
stringToProxyon the communicator, with the string
"SimplePrinter:default -p 10000". Note that the string contains the object identity and the port number that were used by the server. (Obviously, hard-coding object identities and port numbers into our applications is a bad idea, but it will do for now; we will see more architecturally sound ways of doing this when we discuss IceGrid.)
- The proxy returned by
stringToProxyis of type
Ice::ObjectPrx, which is at the root of the inheritance tree for interfaces. But to actually talk to our printer, we need a proxy for a
Printerinterface, not an
Objectinterface. To do this, we need to do a down-cast by calling
PrinterPrx::checkedCast. A checked cast sends a message to the server, effectively asking "is this a proxy for a
Printerinterface?" If so, the call returns a proxy to a
Printer; otherwise, if the proxy denotes an interface of some other type, the call returns a null proxy.
- We test that the down-cast succeeded and, if not, throw an error message that terminates the client.
- We now have a live proxy in our address space and can call the
printStringmethod, passing it the time-honored
"Hello World!"string. The server prints that string on its terminal.
Compiling and linking the client looks much the same as for the server:
Running Client and Server in C++
To run client and server, we first start the server in a separate window:
At this point, we won't see anything because the server simply waits for a client to connect to it. We run the client in a different window:
The client runs and exits without producing any output; however, in the server window, we see the
"Hello World!" that is produced by the printer. To get rid of the server, we interrupt it on the command line for now.
If anything goes wrong, the client will print an error message. For example, if we run the client without having first started the server, we get: