NAME

       gd_bof — report the start of data in a field

SYNOPSIS

       #include <getdata.h>

       off_t gd_bof(DIRFILE *dirfile, const char *field_code);

DESCRIPTION

       The  gd_bof()  function queries a dirfile(5) database specified by dirfile and returns the
       sample number of the beginning-of-field marker for the vector field given by field_code.

       The caller should not assume that the beginning-of-field marker falls on a frame boundary.
       The beginning-of-field marker is never negative.

       For a RAW field, the beginning-of-field corresponds to the frame offset of that field (see
       gd_frameoffset(3)).  The beginning-of-field for all other vector field type is the same as
       the  beginning-of-field  of  whichever  of  its  input  fields  that  starts  latest.  The
       beginning-of-field marker for the special field INDEX is always zero.

       The beginning-of-field marker for a field containing no data is in the same  location  as,
       or  after,  its  end-of-field  marker  (see  gd_eof(3)).   For a RAW field, the difference
       between the locations of the beginning- and end-of-field markers indicates the  number  of
       samples of data actually stored on disk.

       The  dirfile argument must point to a valid DIRFILE object previously created by a call to
       gd_open(3).

RETURN VALUE

       Upon successful completion, gd_bof() returns the sample number of the end-of-field  marker
       for the indicated field.  On error, it returns -1 and sets the dirfile error to a non-zero
       error value.  Possible error values are:

       GD_E_BAD_CODE
               The field specified by field_code or one of the fields it uses as  input  was  not
               found in the database.

       GD_E_BAD_DIRFILE
               The supplied dirfile was invalid.

       GD_E_BAD_REPR
               The representation suffix specified in field_code, or in one of its inputs was not
               recognised.

       GD_E_DIMENSION
               A scalar field was found where a vector field was expected in  the  definition  of
               field_code  or  one  of  its  inputs, or else field_code itself specified a scalar
               field.

       GD_E_RECURSE_LEVEL
               Too many levels of recursion were encountered while trying to resolve  field_code.
               This  usually  indicates  a  circular  dependency  in  field  specification in the
               dirfile.

       The dirfile error may be retrieved by calling gd_error(3).  A descriptive error string for
       the last error encountered can be obtained from a call to gd_error_string(3).

SEE ALSO

       dirfile(5),  dirfile-encoding(5),  gd_open(3), gd_eof(3), gd_error(3), gd_error_string(3),
       gd_nframes(3)