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NAME | LIBRARY | SYNOPSIS AND DESCRIPTION | ATTRIBUTES | SEE ALSO | COLOPHON |
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xdr(3) Library Functions Manual xdr(3)
xdr - library routines for external data representation
Standard C library (libc, -lc)
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 typeof(bool_t (XDR *, void *, ...)) *xdrproc_t;
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 xdr_bytes(),
xdr_opaque(), or xdr_string().
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: xdr_inline() may return NULL (0) if it cannot
allocate a contiguous piece of a buffer. Therefore the
behavior may vary among stream instances; it exists for the
sake of efficiency.
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,
typeof(int (char *, char *, int)) *readit,
typeof(int (char *, char *, int)) *writeit);
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 op
field must be set by the caller.
Warning: to read from an XDR stream created by this API,
you'll need to call xdrrec_skiprecord() 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 xdr*_create APIs
are not compatible for the same reason.
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 xdr_pointer() instead.
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).
Warning: the destroy routine associated with such XDR
streams calls fflush(3) on the file stream, but never
fclose(3).
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: sp is the address of
the string's pointer. This routine returns one if it
succeeds, zero otherwise.
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 int *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, enum_t *dscmp, char *unp,
const 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 │
├──────────────────────────────────────┼───────────────┼─────────┤
│ xdr_array(), xdr_bool(), │ Thread safety │ MT-Safe │
│ xdr_bytes(), xdr_char(), │ │ │
│ xdr_destroy(), xdr_double(), │ │ │
│ xdr_enum(), xdr_float(), xdr_free(), │ │ │
│ xdr_getpos(), xdr_inline(), │ │ │
│ xdr_int(), xdr_long(), │ │ │
│ xdrmem_create(), xdr_opaque(), │ │ │
│ xdr_pointer(), xdrrec_create(), │ │ │
│ xdrrec_eof(), xdrrec_endofrecord(), │ │ │
│ xdrrec_skiprecord(), │ │ │
│ xdr_reference(), xdr_setpos(), │ │ │
│ xdr_short(), xdrstdio_create(), │ │ │
│ xdr_string(), xdr_u_char(), │ │ │
│ xdr_u_int(), xdr_u_long(), │ │ │
│ xdr_u_short(), xdr_union(), │ │ │
│ xdr_vector(), xdr_void(), │ │ │
│ xdr_wrapstring() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘
rpc(3)
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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Linux man-pages 6.10 2025-01-05 xdr(3)
Pages that refer to this page: rpc(3)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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