CPI Communications programs communicate with each other by making program calls. These calls are used to establish the characteristics of the conversation and to exchange data and control information between the programs. An example of a conversation characteristic is the send_receive_mode characteristic, which indicates whether or not both programs may send data at the same time. Conversation characteristics are discussed in greater detail in "Conversation Characteristics".
When a program makes a CPI Communications call, the program passes characteristics and data to CPI Communications using input parameters. When the call completes, CPI Communications passes data and status information back to the program using output parameters.
The return_code output parameter is returned for all CPI Communications calls. It indicates whether a call completed successfully or if an error was detected that caused the call to fail. CPI Communications uses additional output parameters on some calls to pass status information to the program. These parameters include the control_information_received, data_received, and status_received parameters. Additionally, the return code may be associated with secondary information, which can be used to determine the cause of the return code.
The following six calls are called the starter set.
These six calls, which provide the core function, allow for simple communication of data between two programs. They are sufficient for writing simple applications that use the initial values for the CPI-C conversation characteristics. They are necessary for writing very complex applications. Example flows using these calls are provided in "Starter-Set Flows".