An ESP function should have the following basic structure with regard to its interaction with the Open Server API:
Get the number of parameters.
Get the values of the input/output parameters and bind them to local variables.
Perform the processing using the input parameter values and store the results in local variables.
Initialize any output parameters with appropriate values, bind them with local variables, and transfer them to the client.
Use srv_sendinfo() to send the returned row to the client.
Use srv_sendstatus() to send the status to the client.
Use srv_senddone() to inform the client that the processing is done.
If there is an error condition, use srv_sendinfo() to send the error message to the client.
See the Open Server Server-Library/C Reference Manual for documentation of the Open Server routines.