SOAP is a firewalls friendly way to make remote procedures call.. SOAP may also be used over HTTPS (since it is the same protocol as HTTP at the application level).
First you need to compile schema(xsd file).
http://users.skynet.be/pascalbotte/rcx-ws-doc/gsoap.htm
The following files will be created after compiling schema :
soapC.c soapencoder.c
soapencoder.h soapH.h soapStub.h stdsoap2.h
soapencode : It is the function to convert structure to xml stream.
soapdecode : It is the function to convert xml stream to structure.
Now you can send xml stream using curl library.