Module openj9.dtfj

Package com.ibm.dtfj.corereaders.zos.util

Class Clib

java.lang.Object

com.ibm.dtfj.corereaders.zos.util.Clib

public class Clib
extends Object

This class provides a low level interface to some of the z/OS C library. This approach was inspired by the SWT design in that we have a one-to-one mapping between JNI calls and C library calls: no extra work is done in the native functions. This is much easier to maintain because this library should rarely need recompiling.

Please refer to the C library documentation for more details about arguments to these calls.

Field Summary

Fields

Modifier and Type	Field	Description
static int	SEEK_CUR	fseek whence argument to indicate that offset is from the current position of the file pointer
static int	SEEK_END	fseek whence argument to indicate that offset is from the end of the file
static int	SEEK_SET	fseek whence argument to indicate that offset is from the beginning of the file

Constructor Summary

Constructors

Constructor	Description
Clib()

Method Summary

Modifier and Type	Method	Description
static int	fgetpos(long fp, int[] pos)	This method is a wrapper around fgetpos.
static long	fopen(byte[] filename, byte[] mode)	This method is a wrapper around fopen.
static long	fopen(String filename, String mode)	This method is a slightly friendlier version of the native fopen call (the parameters are Strings rather than byte arrays otherwise everything is the same).
static int	fread(byte[] buf, int size, int count, long fp)	This method is a wrapper around fread.
static int	fseek(long fp, long offset, int whence)	This method is a wrapper around fseek.
static int	fsetpos(long fp, int[] pos)	This method is a wrapper around fsetpos.
static void	perror(byte[] prefix)	This method is a wrapper around perror.
static void	perror(String prefix)	Friendlier version of the native perror call that accepts a String parameter.

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SEEK_SET

public static final int SEEK_SET

fseek whence argument to indicate that offset is from the beginning of the file

See Also:

Constant Field Values

SEEK_CUR

public static final int SEEK_CUR

fseek whence argument to indicate that offset is from the current position of the file pointer

See Also:

Constant Field Values

SEEK_END

public static final int SEEK_END

fseek whence argument to indicate that offset is from the end of the file

See Also:

Constant Field Values

Constructor Detail

Clib

public Clib()

Method Detail

fopen

public static long fopen(byte[] filename,
                         byte[] mode)

This method is a wrapper around fopen.

Parameters:

filename - the name of the file to open as a null-terminated ebcdic byte array

mode - the open mode which must be a null-terminated ebcdic byte array. See the C library fopen documentation for more details

Returns:

the FILE stream pointer from fopen cast to a long

fopen

public static long fopen(String filename,
                         String mode)

This method is a slightly friendlier version of the native fopen call (the parameters are Strings rather than byte arrays otherwise everything is the same).

fgetpos

public static int fgetpos(long fp,
                          int[] pos)

This method is a wrapper around fgetpos. Here we make use of the knowledge that a C fpos_t on z/OS is actually an array of 8 ints.

Parameters:

fp - the stream obtained from an earlier call to fopen

pos - this must be an array of 8 ints. The position indicator is stored in this array. The same array contents may be passed to a subsequent fsetpos call.

Returns:

the return code from the fgetpos call (zero if successful)

fsetpos

public static int fsetpos(long fp,
                          int[] pos)

This method is a wrapper around fsetpos.

Parameters:

fp - the stream obtained from an earlier call to fopen

pos - this must be an array of 8 ints whose contents were obtained in a previous call to fgetpos.

Returns:

the return code from the fsetpos call (zero if successful)

fseek

public static int fseek(long fp,
                        long offset,
                        int whence)

This method is a wrapper around fseek. (Note: this hasn't been tested for seeks over 2GB yet).

Parameters:

fp - the stream obtained from an earlier call to fopen

offset - the offset to seek to

whence - specifies where to seek from

Returns:

the return code from the fseek call (zero if successful)

fread

public static int fread(byte[] buf,
                        int size,
                        int count,
                        long fp)

This method is a wrapper around fread.

Parameters:

buf - the buffer to contain the read data

size - the size of each element

count - the number of elements to read

fp - the stream obtained from an earlier call to fopen

Returns:

the number of elements read

perror

public static void perror(byte[] prefix)

This method is a wrapper around perror.

Parameters:

prefix - the message prefix as a null-terminated ebcdic byte array

perror

public static void perror(String prefix)

Friendlier version of the native perror call that accepts a String parameter.