You can make an RFC call and receive return values using a single function:

RFC_RC SAP_API RfcCallReceiveExt(RFC_HANDLE handle,
char * function,
char ** exception);

This function waits till it receives an answer before returning. The return values are just the same as those you would receive by calling RfcReceiveExt. (See the RfcReceiveExt function for a list of return values.)

RfcCallReceiveExt can fail because you called RfcOpenExt with an invalid password. See RfcOpenExt for more information.