xdr — library routines for external data representation
These routines allow C programmers to describe arbitrary data structures in a machine-independent fashion. Data for remote procedure calls are transmitted using these routines.
The prototypes below are declared in <
rpc/xdr.h
>
and make use of the following types:
typedef int bool_t;typedef bool_t
(*xdrproc_t) (XDR *
,void *
,...
);
For the declaration of the XDR
type, see <
rpc/xdr.h
>
bool_t
xdr_array( |
XDR *xdrs, |
char **arrp, | |
unsigned int *sizep, | |
unsigned int maxsize, | |
unsigned int elsize, | |
xdrproc_t elproc) ; |
A filter primitive that translates between
variable-length arrays and their corresponding
external representations. The argument arrp
is the address of
the pointer to the array, while sizep
is the address of
the element count of the array; this element count
cannot exceed maxsize
. The argument
elsize
is the
sizeof
each of the
array's elements, and elproc
is an XDR filter
that translates between the array elements' C form,
and their external representation. This routine
returns one if it succeeds, zero otherwise.
bool_t
xdr_bool( |
XDR *xdrs, |
bool_t *bp) ; |
A filter primitive that translates between booleans (C integers) and their external representations. When encoding data, this filter produces values of either one or zero. This routine returns one if it succeeds, zero otherwise.
bool_t
xdr_bytes( |
XDR *xdrs, |
char **sp, | |
unsigned int *sizep, | |
unsigned int maxsize) ; |
A filter primitive that translates between counted
byte strings and their external representations. The
argument sp
is the address of the string pointer. The length of
the string is located at address sizep
; strings cannot
be longer than maxsize
. This routine
returns one if it succeeds, zero otherwise.
bool_t
xdr_char( |
XDR *xdrs, |
char *cp) ; |
A filter primitive that translates between C characters and their external representations. This routine returns one if it succeeds, zero otherwise.
Note | |
---|---|
Encoded characters are not packed, and
occupy 4 bytes each. For arrays of
characters, it is worthwhile to consider
|
void
xdr_destroy( |
XDR *xdrs) ; |
A macro that invokes the destroy routine
associated with the XDR stream, xdrs
. Destruction
usually involves freeing private data structures
associated with the stream. Using xdrs
after invoking
xdr_destroy
() is
undefined.
bool_t
xdr_double( |
XDR *xdrs, |
double *dp) ; |
A filter primitive that translates between C double precision numbers and their external representations. This routine returns one if it succeeds, zero otherwise.
bool_t
xdr_enum( |
XDR *xdrs, |
enum_t *ep) ; |
A filter primitive that translates between C enums (actually integers) and their external representations. This routine returns one if it succeeds, zero otherwise.
bool_t
xdr_float( |
XDR *xdrs, |
float *fp) ; |
A filter primitive that translates between C floats and their external representations. This routine returns one if it succeeds, zero otherwise.
void
xdr_free( |
xdrproc_t proc, |
char *objp) ; |
Generic freeing routine. The first argument is the XDR routine for the object being freed. The second argument is a pointer to the object itself.
Note | |
---|---|
The pointer passed to this routine is not freed, but what it points to is freed (recursively). |
unsigned int
xdr_getpos( |
XDR *xdrs) ; |
A macro that invokes the get-position routine
associated with the XDR stream, xdrs
. The routine
returns an unsigned integer, which indicates the
position of the XDR byte stream. A desirable feature
of XDR streams is that simple arithmetic works with
this number, although the XDR stream instances need
not guarantee this.
long
*xdr_inline( |
XDR *xdrs, |
int len) ; |
A macro that invokes the inline routine associated
with the XDR stream, xdrs
. The routine
returns a pointer to a contiguous piece of the
stream's buffer; len
is the byte length
of the desired buffer.
Note | |
---|---|
Pointer is cast to long *. |
Warning | |
---|---|
|
bool_t
xdr_int( |
XDR *xdrs, |
int *ip) ; |
A filter primitive that translates between C integers and their external representations. This routine returns one if it succeeds, zero otherwise.
bool_t
xdr_long( |
XDR *xdrs, |
long *lp) ; |
A filter primitive that translates between C long integers and their external representations. This routine returns one if it succeeds, zero otherwise.
void
xdrmem_create( |
XDR *xdrs, |
char *addr, | |
unsigned int size, | |
enum xdr_op op) ; |
This routine initializes the XDR stream object
pointed to by xdrs
. The stream's data
is written to, or read from, a chunk of memory at
location addr
whose length is no more than size
bytes long. The
op
determines
the direction of the XDR stream (either XDR_ENCODE
, XDR_DECODE
, or XDR_FREE
).
bool_t
xdr_opaque( |
XDR *xdrs, |
char *cp, | |
unsigned int cnt) ; |
A filter primitive that translates between fixed
size opaque data and its external representation. The
argument cp
is the address of the opaque object, and cnt
is its size in
bytes. This routine returns one if it succeeds, zero
otherwise.
bool_t
xdr_pointer( |
XDR *xdrs, |
char **objpp, | |
unsigned int objsize, | |
xdrproc_t xdrobj) ; |
Like xdr_reference
()
except that it serializes null pointers, whereas
xdr_reference
() does
not. Thus, xdr_pointer
() can represent
recursive data structures, such as binary trees or
linked lists.
void
xdrrec_create( |
XDR *xdrs, |
unsigned int sendsize, | |
unsigned int recvsize, | |
char *handle, | |
int (*readit)( char *,
char *, int) , |
|
int (*writeit)( char *,
char *, int) ) ; |
This routine initializes the XDR stream object
pointed to by xdrs
. The stream's data
is written to a buffer of size sendsize
; a value of
zero indicates the system should use a suitable
default. The stream's data is read from a buffer of
size recvsize
; it too can be
set to a suitable default by passing a zero value.
When a stream's output buffer is full, writeit
is called.
Similarly, when a stream's input buffer is empty,
readit
is
called. The behavior of these two routines is similar
to the system calls read(2) and
write(2), except
that handle
is passed to the former routines as the first
argument.
Note | |
---|---|
The XDR stream's |
Warning | |
---|---|
To read from an XDR stream created by this
API, you'll need to call xdrrec_skiprecord(3)
first before calling any other XDR APIs. This
inserts additional bytes in the stream to
provide record boundary information. Also,
XDR streams created with different
|
bool_t
xdrrec_endofrecord( |
XDR *xdrs, |
int sendnow) ; |
This routine can be invoked only on streams
created by xdrrec_create
(). The data in the
output buffer is marked as a completed record, and
the output buffer is optionally written out if
sendnow
is
nonzero. This routine returns one if it succeeds,
zero otherwise.
bool_t
xdrrec_eof( |
XDR *xdrs) ; |
This routine can be invoked only on streams
created by xdrrec_create
(). After consuming
the rest of the current record in the stream, this
routine returns one if the stream has no more input,
zero otherwise.
bool_t
xdrrec_skiprecord( |
XDR *xdrs) ; |
This routine can be invoked only on streams
created by xdrrec_create
(). It tells the XDR
implementation that the rest of the current record in
the stream's input buffer should be discarded. This
routine returns one if it succeeds, zero
otherwise.
bool_t
xdr_reference( |
XDR *xdrs, |
char **pp, | |
unsigned int size, | |
xdrproc_t proc) ; |
A primitive that provides pointer chasing within
structures. The argument pp
is the address of
the pointer; size
is the
sizeof
the structure
that *pp
points to; and proc
is an XDR
procedure that filters the structure between its C
form and its external representation. This routine
returns one if it succeeds, zero otherwise.
Warning | |
---|---|
This routine does not understand null
pointers. Use |
bool_t
xdr_setpos( |
XDR *xdrs, |
unsigned int pos) ; |
A macro that invokes the set position routine
associated with the XDR stream xdrs
. The argument
pos
is a
position value obtained from xdr_getpos
(). This routine returns
one if the XDR stream could be repositioned, and zero
otherwise.
Warning | |
---|---|
It is difficult to reposition some types of XDR streams, so this routine may fail with one type of stream and succeed with another. |
bool_t
xdr_short( |
XDR *xdrs, |
short *sp) ; |
A filter primitive that translates between C short integers and their external representations. This routine returns one if it succeeds, zero otherwise.
void
xdrstdio_create( |
XDR *xdrs, |
FILE *file, | |
enum xdr_op op) ; |
This routine initializes the XDR stream object
pointed to by xdrs
. The XDR stream
data is written to, or read from, the stdio
stream file
. The argument
op
determines
the direction of the XDR stream (either XDR_ENCODE
, XDR_DECODE
, or XDR_FREE
).
bool_t
xdr_string( |
XDR *xdrs, |
char **sp, | |
unsigned int maxsize) ; |
A filter primitive that translates between C
strings and their corresponding external
representations. Strings cannot be longer than
maxsize
.
Note | |
---|---|
|
bool_t
xdr_u_char( |
XDR *xdrs, |
unsigned char *ucp) ; |
A filter primitive that translates between unsigned C characters and their external representations. This routine returns one if it succeeds, zero otherwise.
bool_t
xdr_u_int( |
XDR *xdrs, |
unsigned *up) ; |
A filter primitive that translates between C unsigned integers and their external representations. This routine returns one if it succeeds, zero otherwise.
bool_t
xdr_u_long( |
XDR *xdrs, |
unsigned long *ulp) ; |
A filter primitive that translates between C unsigned long integers and their external representations. This routine returns one if it succeeds, zero otherwise.
bool_t
xdr_u_short( |
XDR *xdrs, |
unsigned short *usp) ; |
A filter primitive that translates between C unsigned short integers and their external representations. This routine returns one if it succeeds, zero otherwise.
bool_t
xdr_union( |
XDR *xdrs, |
int *dscmp, | |
char *unp, | |
struct xdr_discrim *choices, | |
xdrproc_t defaultarm) ; |
/* may equal NULL */
A filter primitive that translates between a
discriminated C union and its
corresponding external representation. It first
translates the discriminant of the union located at
dscmp
. This
discriminant is always an enum_t. Next the union located at
unp
is
translated. The argument choices
is a pointer to
an array of xdr_discrim
() structures. Each
structure contains an ordered pair of [value
,proc
]. If the union's
discriminant is equal to the associated value
, then the
proc
is
called to translate the union. The end of the
xdr_discrim
() structure
array is denoted by a routine of value NULL. If the
discriminant is not found in the choices
array, then the
defaultarm
procedure is called (if it is not NULL). Returns one
if it succeeds, zero otherwise.
bool_t
xdr_vector( |
XDR *xdrs, |
char *arrp, | |
unsigned int size, | |
unsigned int elsize, | |
xdrproc_t elproc) ; |
A filter primitive that translates between
fixed-length arrays and their corresponding external
representations. The argument arrp
is the address of
the pointer to the array, while size
is the element
count of the array. The argument elsize
is the
sizeof
each of the
array's elements, and elproc
is an XDR filter
that translates between the array elements' C form,
and their external representation. This routine
returns one if it succeeds, zero otherwise.
bool_t
xdr_void( |
void) ; |
This routine always returns one. It may be passed to RPC routines that require a function argument, where nothing is to be done.
bool_t
xdr_wrapstring( |
XDR *xdrs, |
char **sp) ; |
A primitive that calls xdr_string(xdrs, sp,MAXUN.UNSIGNED
); where MAXUN.UNSIGNED
is the
maximum value of an unsigned integer. xdr_wrapstring
() is handy because
the RPC package passes a maximum of two XDR routines
as arguments, and xdr_string
(), one of the most
frequently used primitives, requires three. Returns
one if it succeeds, zero otherwise.
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value |
xdrrec_eof (),xdrrec_endofrecord (),xdrrec_skiprecord (),
|
Thread safety | MT-Safe |
The following manuals:
eXternal Data Representation Standard: Protocol Specification
eXternal Data Representation: Sun Technical Notes
XDR: External Data Representation Standard, RFC 1014, Sun Microsystems, Inc., USC-ISI.
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