NAME

       gd_alter_entry — modify the metadata of a dirfile field

SYNOPSIS

       #include <getdata.h>

       int gd_alter_entry(DIRFILE *dirfile, const char *field_code, const gd_entry_t *entry, int recode);

DESCRIPTION

       The  gd_alter_entry()  function  modifies  the  field specified by field_code in the dirfile specified by
       dirfile to correspond to the new parameters specified by entry.  In  addition  to  specifying  a  regular
       field,  field_code  may  also  refer to a metafield by specifying it using its full (slashed) field code.
       However, field_code should never contain a representation suffix.

       The form of entry is described in detail in the get_entry(3) man page.  The entry->field and entry->frag‐
       ment_index members are ignored by this function and need not be initialised.  All other members appropri‐
       ate to the field type of field_code should be initialised, except as noted below.  To change the fragment
       index of a field, use gd_move(3).  To change the name of a field, use gd_rename(3).

       The only flags in the entry->flags member which are honoured are GD_EN_HIDDEN, which  should  be  set  or
       cleared  to  set  the  hiddenness  of  the  entry (see gd_hidden(3)), and GD_EN_COMPSCAL, which indicates
       whether scalar parameters are initialised from the complex valued or purely real member, which  both  are
       present (LINCOM, POLYNOM, RECIP).

       If  field_code specifies a RAW field and the recode argument is non-zero, the binary file associated with
       the field will be converted for changes in data type and samples-per-frame.  In this  case,  the  field's
       I/O  pointer  will be reset to the beginning-of-frame.  If recode is zero, no binary file conversion will
       take place.

       If field_code specifies a LINTERP field and the recode argument is non-zero, the look-up table file  will
       be  moved if entry->table specifies a different path.  If a file with the new pathname already exists, it
       will be overwritten.  If the field specified by field_code is of type other than RAW or LINTERP, the  re‐
       code argument is ignored.

       If  field_code  specified  a LINCOM or POLYNOM field, the value of entry->comp_scal indicates whether the
       purely real scalar lists (entry->a, or entry->b and entry->m) or the complex valued lists (entry->ca,  or
       entry->cb and entry->cm) will be used.  The unused counterparts need not be initialised.

       The  entry->field_type  member must correspond to the field type of field_code.  This interface cannot be
       used to change the type of a given field.  To do so, delete the old field first  with  gd_delete(3),  and
       then create a new field of the desired type with gd_add(3).

       Some entry members have special values which indicate no change should be made to the member.  These spe‐
       cial values are:

       NULL:  any of the string members, also m, b, a, cm, cb, or ca;

       0:     spf, n_fields, numbits, cdividend, dividend, or array_len;

       -1:    bitnum or period;

       GD_NULL:
              data_type or const_type;

       GD_WINDOP_UNK:
              windop.

       All  entry->scalar elements relevant for the given field type must be initialised to one of the following
       values:

       •   a pointer to a field code indicating a new scalar field to be used for the corresponding field  para‐
           meter.   If the parameter was previously a literal number, it will be replaced by the specified field
           code.  If the parameter was previously a field code, the new field code will replace the old one.  If
           the field code specifies a CARRAY field, the corresponding entry->scalar_ind element should  also  be
           set.

       •   a pointer to the empty string ("").  In this case, no change is made to the field code for the corre‐
           sponding field parameter: if one already existed, it is kept, otherwise the corresponding literal nu‐
           merical  parameter  is used.  If the value of the corresponding numerical entry member is the special
           value listed above indicating no change, no change is made to the field parameter at all.

       •   the NULL pointer.  If the corresponding field parameter was previously a field code, the  field  code
           will be deleted and a literal number used instead.  In the special case when a scalar element is NULL
           and  the  corresponding  numerical  entry member contains a special value indicating no change listed
           above, GetData will de-reference the previous field code value and convert it into a  literal  number
           before removing the field code from the entry.

       If  this  function  is  used  to increase the length of a CARRAY field, the added elements will be unini‐
       tialised.  Use gd_put_carray_slice(3) or equivalent to initialise them.

RETURN VALUE

       On success, gd_alter_entry() returns zero.   On error, -1 is returned and the dirfile error is set  to  a
       non-zero error value.  Possible error values are:

       GD_E_ACCMODE
               The specified dirfile was opened read-only.

       GD_E_ALLOC
               The library was unable to allocate memory.

       GD_E_BAD_CODE
               The  field specified by field_code was not found or a supplied field code did not contain the ap‐
               propriate prefix or suffix.  This error may also result from attempting to dereference  a  scalar
               field code which indicates a non-existent field.

       GD_E_BAD_DIRFILE
               The supplied dirfile was invalid.

       GD_E_BAD_ENTRY
               One or more of the parameters specified in entry was invalid.

       GD_E_BAD_FIELD_TYPE
               The  entry->field_type  parameter  did  not  correspond  to  the  type  of the field specified by
               field_code, or an attempt was made to modify the immutable INDEX field.  This error may also  re‐
               sult from attempting to dereference a scalar field code which does not indicate a CONST or CARRAY
               field.

       GD_E_BAD_TYPE
               The entry->data_type parameter provided with a RAW entry, or the entry->const_type parameter pro‐
               vided with a CONST or CARRAY entry, was invalid.

       GD_E_IO An  I/O error occurred while translating the binary file associated with a modified RAW field, or
               an I/O error occurred while attempting to rename a LINTERP table file.

       GD_E_PROTECTED
               The metadata of the fragment was protected from change.  Or, a request to  translate  the  binary
               file associated with a RAW field was attempted, but the data of the fragment was protected.

       GD_E_UNKNOWN_ENCODING
               The  encoding  scheme of the indicated format specification fragment is not known to the library.
               As a result, the library was unable to translate the binary file be associated  with  a  modified
               RAW field.

       GD_E_UNSUPPORTED
               The  encoding  scheme of the indicated format specification fragment does not support translating
               the binary file associated with a modified RAW field.

       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

       gd_alter_bit(3), gd_alter_carray(3), gd_alter_const(3),  gd_alter_divide(3),  gd_alter_lincom(3),  gd_al‐
       ter_linterp(3),  gd_alter_multiply(3),  gd_alter_phase(3),  gd_alter_polynom(3),  gd_alter_raw(3), gd_al‐
       ter_recip(3), gd_alter_spec(3),  gd_delete(3),  gd_error(3),  gd_error_string(3),  gd_hidden(3),  gd_mal‐
       ter_spec(3),  gd_metaflush(3), gd_move(3), gd_open(3), gd_put_carray_slice(3), gd_rename(3), dirfile-for‐
       mat(5)

Version 0.9.0                                    16 October 2014                               gd_alter_entry(3)