NAME

get_entry --- retrieve a dirfile field's metadata

SYNOPSIS

#include <getdata.h>
int get_entry(DIRFILE *dirfile, const char *field_code, gd_entry_t *entry);

DESCRIPTION

The get_entry() function queries a dirfile(5) database specified by dirfile and returns the metadata associated with the field specified by field_code. If field_code contains a valid representation suffix, the suffix will be ignored.

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

The entry will be stored in the gd_entry_t structure indicated by the entry argument, which must be allocated by the caller. Members available in this structure depend on the field type of the field queried. See below for a complete description of this data type.

Strings members in entry filled by this function (variously, depending on field type: field, the elements of the in_fields[] array, table; see below) will by dynamically allocated by get_entry() and should not point to allocated memory locations before calling this function. Only strings provided by the gd_entry_t for the particular field type described will be allocated. These strings should be deallocated with free(3) by the caller once they are no longer needed. The dirfile_free_entry_strings(3) function is provided as a convenience to do this.

The returned entry structure, including strings and their pointers may be freely modified by the caller.

RETURN VALUE

Upon successful completion, get_entry() returns zero, and writes the field metadata in the supplied gd_entry_t buffer. On error, the supplied gd_entry_t buffer is not modified. In this case, get_entry() 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 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 was not recognised.
GD_E_BAD_SCALAR
A scalar parameter used in the definition of the field was invalid. The dirfile error may be retrieved by calling get_error(3). A descriptive error string for the last error encountered can be obtained from a call to get_error_string(3).

THE ENTRY TYPE

Members available in the gd_entry_t structure depend on the field type described. All gd_entry_t objects are guaranteed to have at least:

typedef struct {
  ...

  const char  *field;          /* field code */
  gd_entype_t  field_type;     /* field type */
  int          fragment_index; /* format file fragment index */

  ...
} gd_entry_t;
The field member is the field code of the entry (i.e. its string name). If the call to get_entry(3) is successful, this will be the field name specified as part of the field_code argument. The field_type member indicates the field type of the entry. This is an integer type equal to one of the following symbols:
GD_BIT_ENTRY,~GD_CONST_ENTRY,~GD_INDEX_ENTRY,~ GD_LINCOM_ENTRY,~GD_LINTERP_ENTRY,~GD_MULTIPLY_ENTRY,~ GD_PHASE_ENTRY,~GD_POLYNOM_ENTRY,~GD_RAW_ENTRY,~GD_SBIT_ENTRY,~ GD_STRING_ENTRY. GD_INDEX_ENTRY is a special field type used only for the implicit INDEX field. The meaning of the other symbols should be self-explanatory. The fragment_index member indicates the format file fragment in which this field is defined. This is an integer index to the Dirfile's list of parsed format file fragments. The name of the file corresponding to fragment_index may be obtained by calling get_fragmentname(3). A value of zero for this field indicates that the field is defined in the primary format file, the file called format in the root dirfile directory (see dirfile(5)). Remaining fields in the gd_entry_t structure depend on the value of field_type. Callers are advised to check field_type before attempting to access the remaining members. Members for different field types may be stored in the same physical location in core. Accordingly, attempting to access a member not declared for the appropriate field type will have unspecified results.

BIT and SBIT Members

A gd_entry_t describing a BIT or SBIT entry, will also provide:

typedef struct {
  ...

  const char *in_fields[1];     /* input field code */
  const char *scalar[2];        /* parameter field codes */
  gd_bit_t    bitnum;           /* first bit */
  gd_bit_t    numbits;          /* bit length */

  ...
} gd_entry_t;
The in_fields member is an array of length one containing the input field code. The scalar member is an array of length two containing the field codes specifying bitnum and numbits, or NULLs if numeric literal parameters were used. The bitnum member indicates the number of the first bit (counted from zero) extracted from the input. The gd_bit_t type is a signed 16-bit integer type. If this value was specified as a CONST field code, this will be the numerical value of that field, and scalar[0] will contain the field code itself, otherwise scalar[0] will be NULL. The numbits member indicates the number of bits which are extracted from the input. If this value was specified as a CONST field code, this will be the numerical value of that field, and scalar[1] will contain the field code itself, otherwise scalar[1] will be NULL.

CONST Members

A gd_entry_t describing a CONST entry, will also provide:

typedef struct {
  ...

  gd_type_t   const_type;       /* data type in format file */

  ...
} gd_entry_t;
The const_type member indicates the data type of the constant value stored in the format file metadata. See getdata(3) for a list of valid values that a variable of type gd_type_t may take.

INDEX Members

A gd_entry_t describing an INDEX entry, which is used only for the implicit INDEX field, provides no additional data.

LINCOM Members

A gd_entry_t describing a LINCOM entry, will also provide:

typedef struct {
  ...

  int            n_fields;                  /* # of input fields */
  int            comp_scal;                 /* complex scalar flag */
  const char    *in_fields[GD_MAX_LINCOM];  /* input field code(s) */
  const char    *scalar[2 * GD_MAX_LINCOM]; /* param. field codes */
  double complex cm[GD_MAX_LINCOM];         /* scale factor(s) */
  double         m[GD_MAX_LINCOM];          /* scale factor(s) */
  double complex cb[GD_MAX_LINCOM];         /* offset terms(s) */
  double         b[GD_MAX_LINCOM];          /* offset terms(s) */

  ...
} gd_entry_t;
The n_fields member indicates the number of input fields. It will be between one and GD_MAX_LINCOM inclusive, which is defined in getdata.h to the maximum number of input fields permitted by a LINCOM. The comp_scal member is non-zero if any of the scale factors or offset terms have a non-zero imaginary part. (That is, if comp_scal is zero, the elements of cm~and~cb equal the corresponding elements of m~and~b.) members.) The in_fields member is an array of length GD_MAX_LINCOM containing the input field code(s). Only the first n_fields elements of this array are initialised. The remaining elements contain uninitialised data. The scalar member is an array of length twice GD_MAX_LINCOM containing the field codes specifying the slope factors and offset terms for the field, or NULLs if numberical literal parameters were used. The first GD_MAX_LINCOM array elements contain the scale factors. The remaining GD_MAX_LINCOM array elements contain the offset terms. Array elements scalar[i] and scalar[i + GD_MAX_LINCOM], for i~>=~n_fields, contain uninitialised data. The cm and cb members are arrays of the scale factor(s) and offset term(s) for the LINCOM. Only the first n_fields elements of these array contain meaningful data. If any of these values were specified as a CONST field code, this will be the numerical value of that field. The field code corresponding to cm[i] will be stored in scalar[i] and the field code associated with cb[i] will be stored in scalar[i + GD_MAX_LINCOM]. Otherwise the corresponding scalar member will be NULL. See NOTES below on changes to the declaration of cm and cb when using the C89 GetData API. The elements of m and b are the real parts of the corresponding elements of cm and cb.

LINTERP Members

A gd_entry_t describing a LINTERP entry, will also provide:

typedef struct {
  ...

  const char *table             /* linterp table filename */
  const char *in_fields[1];     /* input field code */

  ...
} gd_entry_t;
The table member is the pathname to the look up table on disk. The in_fields member is an array of length one containing the input field code.

MULTIPLY Members

A gd_entry_t describing a MULTIPLY entry, will also provide:

typedef struct {
  ...

  const char *in_fields[2];     /* input field codes */

  ...
} gd_entry_t;
The in_fields member is an array of length two containing the input field codes.

PHASE Members

A gd_entry_t describing a PHASE entry, will also provide:

typedef struct {
  ...

  const char *in_fields[1];     /* input field code */
  const char *scalar[1];        /* parameter field codes */
  gd_shift_t  shift;            /* phase shift */

  ...
} gd_entry_t;
The in_fields member is an array of length one containing the input field code. The scalar member is an array of length one containing the field code specifying shift, or NULL if a numeric literal parameter was used. The shift member indicates the shift in samples. The gd_shift_t type is a 64-bit signed integer type. A positive value indicates a shift forward in time (towards larger frame numbers). If this value was specified as a CONST field code, this will be the numerical value of that field, and scalar[0] will contain the field code itself, otherwise scalar[0] will be NULL.

POLYNOM Members

A gd_entry_t describing a POLYNOM entry, will also provide:

typedef struct {
  ...

  int            poly_ord;                  /* polynomial order */
  int            comp_scal;                 /* complex scalar flag */
  const char    *in_fields[1];              /* input field code(s) */
  const char    *scalar[GD_MAX_POLY_ORD + 1];
                                            /* co-eff. field codes */
  double complex ca[GD_MAX_POLY_ORD + 1];   /* co-efficients(s) */
  double         a[GD_MAX_POLY_ORD + 1];    /* co-efficients(s) */

  ...
} gd_entry_t;
The poly_ord member indicates the order of the polynomial. It will be between one and GD_MAX_POLY_ORD inclusive, which is defined in getdata.h to the maximum order of polynomial permitted by a POLYNOM. The comp_scal member is non-zero if any of the co-efficients have a non-zero imaginary part. (That is, if comp_scal is zero, the elements of ca equal the corresponding elements of a.) The in_fields member is an array of length one containing the input field code. The scalar member is an array of length one more than GD_MAX_POLYORD containing the field codes specifying the co-efficients for the field, or NULLs if numberical literal parameters were used. Only the first poly_ord + 1 elements are initialised. The remaining elements contain uninitialised data. The ca members are arrays of the co-efficient(s) for the POLYNOM. Only the first poly_ord + 1 elements of this array contains meaningful data. If any of these values were specified as a CONST field code, this will be the numerical value of that field. The field code corresponding to ca[i] will be stored in scalar[i]. Otherwise the corresponding scalar member will be NULL. See NOTES below on changes to the declaration of ca when using the C89 GetData API. The elements of a are the real parts of the corresponding elements of ca.

RAW Members

A gd_entry_t describing a RAW entry, will also provide:

typedef struct {
  ...

  const char   *scalar[1];    /* parameter field codes */
  gd_spf_t      spf;          /* samples per frame on disk */
  gd_type_t     data_type;    /* data type on disk */

  ...
} gd_entry_t;
The scalar member is an array of length one containing the field code specifying spf, or NULL if a numeric literal parameter was used. The spf member contains the samples per frame of the binary data on disk. The gd_spf_t type is an unsigned 16-bit integer type. If this value was specified as a CONST field code, this will be the numerical value of that field, and scalar[0] will contain the field code itself, otherwise scalar[0] will be NULL. The data_type member indicates the data type of the binary data on disk. See getdata(3) for a list of valid values that a variable of type gd_type_t may take.

STRING Members

A gd_entry_t describing a STRING entry provides no additional data.

NOTES

When using the C89 GetData API (by defining GETDATA_C89_API before including getdata.h), the complex valued array members of gd_entry_t used in the specification of LINCOM and POLYNOM entries will be replaced by purely real arrays. These will have the prototypes such as:

  double        cm[GD_MAX_LINCOM][2];
  double        cb[GD_MAX_LINCOM][2];
  double        ca[GD_MAX_POLY_ORD + 1][2];
The first element of the two element array is the real part of the complex number, and the second element is the imaginary part.

SEE ALSO

dirfile(5), dirfile_free_entry_strings(3), dirfile_open(3), getdata(3), get_error(3), get_error_string(3), get_field_list(3), get_fragmentname(3), get_raw_filename(3)