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->fragment_index  members  are  ignored  by  this  function  and need not be initialised.  All other
       members appropriate 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).

       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.  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
       recode 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 field parameters have special values which indicate no change  should  be  made  to  the  parameter.
       Specifically,      if      any      of      the      string     parameters,     or     the     parameters
       (entry->a, entry->b, entry->m, entry->ca, entry->cb, or entry->cm) are  NULL,  the  old  values  will  be
       retained.   Similarly,  if entry->spf, entry->n_fields, or entry->numbits is zero, or if entry->bitnum is
       -1, or if entry->data_type, or entry->const_type are equal to  GD_NULL,  these  parameters  will  not  be
       modified.

       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
           parameter.   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 the empty string ("").  In this case,  no  change  is  made  to  the  field  code  for  the
           corresponding  field  parameter:  if  one  already  existed,  it is kept, otherwise the corresponding
           literal numerical 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.

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.  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
               result  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
               provided with a CONST or CARRAY entry, was invalid.

       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_RAW_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_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_alter_linterp(3),  gd_alter_multiply(3),  gd_alter_phase(3),   gd_alter_polynom(3),   gd_alter_raw(3),
       gd_alter_recip(3),  gd_alter_spec(3),  gd_delete(3),  gd_error(3), gd_error_string(3), gd_malter_spec(3),
       gd_metaflush(3), gd_move(3), gd_open(3), gd_rename(3), dirfile-format(5)