Web Services Description Language (WSDL) provides a machine-readable description of how services can be called and how messages should be formed. Like the other W3C web services standards, it is encoded in XML.
It is often used with SOAP to define interfaces that the web service offers and how they may be used.
Once you define your API in WSDL, you may (and should!) use automated tooling to help you create code out of it. For C++, one framework with such tools is gSOAP. It comes with a tool named wsdl2h, which will generate a header file out of the definition. You can then use another tool, soapcpp2, to generate bindings from the interface definition to your implementation.
Unfortunately, due to the verbosity of the messages, the size and bandwidth requirements for SOAP services are generally huge. If this is not an issue, then SOAP can have its uses. It allows for both synchronous and asynchronous calls, as well as stateful and stateless operations. If you require rigid...