
Better use the call
RfcOpenEx.The following function opens an RFC connection.
RFC_HANDLE SAP_API RfcOpenExtV3(char* destination,
RFC_MODE mode,
char* hostname,
int sysnr,
char* gateway_host,
char* gateway_service,
char* client,
char* user,
char* password,
char* language,
int trace
RFC_INT use_load_balancing,
char * lb_host,
char * lb_system_name
char * lb_group
RFC_INT use_sapgui);
All parameters are passed as single fields (using
RFC_MODE).The following parameters are always needed in this call:
RFC_MODE mode and SAP logon information: client, user, password, language, trace, and use_sapgui.The following parameters are necessary, depending on
RFC_MODE:gateway_host, gateway_service, hostname and sysnr can be defined. sideinfo is necessary.
gateway_host and gateway_service can be defined. hostname and sysnr must be defined.
destination, gateway_host, gateway_service, hostname and sysnr will not be evaluated.
lb_host and lb_system_name must be defined. If lb_group is NULL, the group ‘PUBLIC’ will be used.

use_sapgui and ABAP-Debug are only available with R/3 3.0C or later and not on Windows with a 16-bit-RFC-library.
use_sapgui and ABAP-Debug are not available with R/2.
This function is defined in SAPRFC.H.
Return Values:
Function Parameters:
name of destination or NULL
connection mode ( RFC_MODE)
hostname of target system or NULL
system number (0-99)
gateway hostname or NULL
gateway service or NULL
signon data: client
signon data: user
signon data: password
signon data: language
trace (OFF/ON/ABAP-DEBUG or also trace ON and ABAP-DEBUG: 0/1/2/3)
using load balancing feature (OFF/ON/0/1)
host name of the ‘message server’
name of the target system (e.g. C11)
application server group or NULL for PUBLIC
using sapgui to display SAP dynpros and graphics (OFF/ON: 0/1)
See also RfcOpen and RFC_OPTIONS.