HP-UX SNAplus2 R7 APPC Programmer's Guide

APPC Control Verbs
3 APPC Control Verbs
This chapter contains a description of each APPC control verb. The following information is provided for each
verb:
• Definition of the verb.
• Structure defining the verb control block (VCB) used by the verb. The structure is defined in the APPC header
file
/usr/include/sna/appc_c.h(HP-UX) or sdk/winappc.h (Windows). Parameters beginning with
reserv are reserved.
• Parameters (VCB fields) supplied to and returned by APPC. For each parameter, the following information is
provided:
• Description
• Possible values
• Additional information
• Conversation state or states in which the verb can be issued.
• State or states to which the conversation can change upon return from the verb. Conditions that do not cause a
state change are not noted. For example, parameter checks and state checks do not cause a state change.
• Additional information describing the use of the verb.
Most parameters supplied to and returned by APPC are hexadecimal values. To simplify coding, these values are
represented by meaningful symbolic constants defined in the header file values_c.h, which is included by the
APPC header file appc_c.h. For example, the opcode parameter of the TP_STARTED verb is the hexadecimal
value represented by the symbolic constant AP_TP_STARTED. The file values_c.h also includes definitions of
parameter types such as AP_UINT16 that are used in the APPC VCBs.
It is important that you use the symbolic constant and not the hexadecimal value when setting values for supplied
parameters, or when testing values of returned parameters. This is because different HP-UX systems store these
values differently in memory, so the value shown may not be in the format recognized by your system.
WINDOWS
For Windows, the constants for supplied and returned parameter values are defined in the Windows APPC header
file winappc.h.
The notation “[MC_]verb” refers to both the mapped and basic form of an APPC verb. For example,
[MC_]SEND_DATA refers to the MC_SEND_DATA and SEND_DATA verbs.
Note
The APPC VCBs contain many parameters marked as “reserved”; some of these are used
internally by the SNAplus2 software, and others are not used in this version but may be
used in future versions. Your application must not attempt to access any of these reserved
parameters; instead, it must set the entire contents of the VCB to zero to ensure that all of
these parameters are zero, before it sets other parameters that are used by the verb. This
ensures that SNAplus2 will not misinterpret any of its internally-used parameters, and also
that your application will continue to work with future SNAplus2 versions in which these
parameters may be used to provide new functions.
To set the VCB contents to zero, use memset:
memset(vcb, 0, sizeof(vcb));
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