This is the solution.
#include "calc.nsmap"
#include "soapcalcProxy.h" // generated with soapcpp2 -j calc.h
calcProxy calc("https-server-endpoint-URL");
double sum;
soap_ssl_init(); // init SSL (just need to do this once in an application)
// soap_ssl_no_init(); // or prevent init OpenSSL when already initialized elsewhere in an application
if (soap_ssl_client_context(calc.soap,
SOAP_SSL_DEFAULT,
NULL, // no keyfile
NULL, // no keyfile password
"cacerts.pem", // trusted certificates (or use self-signed cacert.pem)
NULL, // no capath to trusted certificates
NULL // no random data to seed randomness
))
{
calc.soap_stream_fault(std::cerr);
exit(EXIT_FAILURE);
}
if (calc.add(1.23, 4.56, sum) == SOAP_OK)