gd_seek(3)

NAME
gd_seek — reposition a Dirfile field pointer

SYNOPSIS
#include <getdata.h>

off_t gd_seek(DIRFILE *dirfile, const char *field_code, off_t frame_num, off_t sample_num, int flags);

DESCRIPTION
The function changes the position of the I/O pointer associated with the field in the dirfile(5) database specified by In normal operation, advances the field I/O pointer frames plus samples from the origin point specified in which should contain one of GD_SEEK_SET, GD_SEEK_CUR, or GD_SEEK_END, indicating, respectively, sample zero, the current position of the field pointer, and the location of the end-of-field marker (see

In addition to one of the symbols above, the parameter may also, optionally, be bitwise or'd with GD_SEEK_WRITE, which will result in the field being padded (with zero for integer types, or a IEEE-754 conforming not-a-number otherwise) in the event of seeking past the end-of-field marker.

The effect of attempting to seek past the end-of-field is encoding specific. Some encodings don't actually add the padding requested by GD_SEEK_WRITE unless a subsequent call is used to add more data to the field at the new end-of-field. Other encodings add the padding, advancing the end-of-field, regardless of subsequent writes. Similarly, attempting to seek past the end-of-field marker in read mode (without specifying GD_SEEK_WRITE) is also encoding specific: in some encodings the field pointer will be moved past the end-of-field marker, while in others, it will be repositioned to the end of field. Check the return value to determine the result.

In general, GD_SEEK_WRITE should be used on calls before a write via while calls before a read via should omit the GD_SEEK_WRITE flag. So the following:

    gd_seek(dirfile, field_code, a, b, GD_SEEK_SET | GD_SEEK_WRITE);
    gd_putdata(dirfile, field_code, GD_HERE, 0, c, d, type, data);

is equivalent to:

    gd_putdata(dirfile, field_code, a, b, c, d, type, data);

and, similarly,

    gd_seek(dirfile, field_code, a, b, GD_SEEK_SET);
    gd_getdata(dirfile, field_code, GD_HERE, 0, c, d, type, data);

is equivalent to:

    gd_getdata(dirfile, field_code, a, b, c, d, type, data);

Only RAW fields (and the implicit INDEX field) have field I/O pointers associated with them. Calling on a derived field will move the field pointers of all of the field's inputs. It is possible to create derived fields which simultaneously read from different places of the same input field. Calling on such a field will result in an error.

RETURN VALUE
Upon successful completion, returns a non-negative integer indicating the I/O position, in samples, of the specified field after performing the seek. On error, it returns a negative-valued error code. Possible error codes are: The library was unable to allocate memory. The parameter didn't contain exactly one of GD_SEEK_SET, GD_SEEK_CUR, or GD_SEEK_END. The field specified by or one of the fields it uses for input, was not found in the database. The supplied dirfile was invalid. An attempt was made to seek relative to GD_SEEK_END on the INDEX field, which has no end-of-field marker. The specified field or one of its inputs wasn't of vector type. The field position couldn't be set due to a derived field reading simultaneously from more than one place in a RAW field. An internal error occurred in the library while trying to perform the task. This indicates a bug in the library. Please report the incident to the maintainer. An error occurred while trying to open or read from a file on disk containing a raw field. The request resulted an attempt to move the I/O pointer of the specified field or one of its inputs to a negative sample number. Too many levels of recursion were encountered while trying to resolve This usually indicates a circular dependency in field specification in the dirfile. The encoding scheme of a RAW field could not be determined. This may also indicate that the binary file associated with the RAW field could not be found. Reading from dirfiles with the encoding scheme of the specified dirfile is not supported by the library. See dirfile-encoding(5) for details on dirfile encoding schemes.

The error code is also stored in the DIRFILE object and may be retrieved after this function returns by calling A descriptive error string for the error may be obtained by calling

HISTORY
The function appeared in GetData-0.8.0.

In GetData-0.10.0, the error return from this function changed from -1 to a negative-valued error code.

SEE ALSO