Exit Program for Change File Pointer (QHFCHGFP) API

Before applications can use the Change File Pointer (QHFCHGFP) API with your file system, you must:

1. Write an exit program that performs the change file pointer operation on behalf of the API. For a detailed description of the API and its calling parameters, see Change File Pointer (QHFCHGFP) API.
   
   
2. Give the exit program's name when you register the file system with the Register File System (QHFRGFS) API.

After that, when an application calls the QHFCHGFP API, the API calls your exit program and passes it the parameters specified by the application. Your exit program performs the work and returns any data to the API. The API passes the data back to the calling application.

Authorities and Locks

None.

Required Parameter Group

The following shows the input parameters that the API passes to your exit program and the output parameter that the exit program must pass back to the API:

Operation (CHGFP)

INPUT; CHAR(5)

The abbreviation for the operation being performed (CHGFP).

File system job handle

INPUT; CHAR(16)

The work area or job identifier for use by the file system.

The following parameters are the same as the parameters for the API.

Open file handle

INPUT; CHAR(16)

Move information

INPUT; CHAR(6)

Distance to move

INPUT; BINARY(4)

New offset

OUTPUT; BINARY(4) UNSIGNED

API Functions

The QHFCHGFP API performs the standard functions described in Standard HFS API Functions.

Exit Program Requirements

You must create an exit program that performs the standard functions described in Standard HFS Exit Program Requirements and these additional functions:

• Checks for an attempt to set the file pointer to a negative position (that is, before the start of the file) or a position beyond the maximum value allowed in a 4-byte unsigned binary number, and signals an error if either occurs.
  
  
• Moves the file pointer the specified distance from the specified starting location, and records the file pointer's new offset value.

Error Messages for Exit Program Use

This section lists the messages that the exit program can return to the API.