1xdr(3) Library Functions Manual xdr(3)
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6 xdr - library routines for external data representation
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9 Standard C library (libc, -lc)
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12 These routines allow C programmers to describe arbitrary data struc‐
13 tures in a machine-independent fashion. Data for remote procedure
14 calls are transmitted using these routines.
15 The prototypes below are declared in <rpc/xdr.h> and make use of the
17 following types:
18 typedef int bool_t;
20 typedef bool_t (*xdrproc_t)(XDR *, void *,...);
22 For the declaration of the XDR type, see <rpc/xdr.h>.
24 bool_t xdr_array(XDR *xdrs, char **arrp, unsigned int *sizep,
26 unsigned int maxsize, unsigned int elsize,
27 xdrproc_t elproc);
28 A filter primitive that translates between variable-length ar‐
30 rays and their corresponding external representations. The ar‐
31 gument arrp is the address of the pointer to the array, while
32 sizep is the address of the element count of the array; this el‐
33 ement count cannot exceed maxsize. The argument elsize is the
34 sizeof each of the array's elements, and elproc is an XDR filter
35 that translates between the array elements' C form, and their
36 external representation. This routine returns one if it suc‐
37 ceeds, zero otherwise.
38 bool_t xdr_bool(XDR *xdrs, bool_t *bp);
40 A filter primitive that translates between booleans (C integers)
42 and their external representations. When encoding data, this
43 filter produces values of either one or zero. This routine re‐
44 turns one if it succeeds, zero otherwise.
45 bool_t xdr_bytes(XDR *xdrs, char **sp, unsigned int *sizep,
47 unsigned int maxsize);
48 A filter primitive that translates between counted byte strings
50 and their external representations. The argument sp is the ad‐
51 dress of the string pointer. The length of the string is lo‐
52 cated at address sizep; strings cannot be longer than maxsize.
53 This routine returns one if it succeeds, zero otherwise.
54 bool_t xdr_char(XDR *xdrs, char *cp);
56 A filter primitive that translates between C characters and
58 their external representations. This routine returns one if it
59 succeeds, zero otherwise. Note: encoded characters are not
60 packed, and occupy 4 bytes each. For arrays of characters, it
61 is worthwhile to consider xdr_bytes(), xdr_opaque(), or
62 xdr_string().
63 void xdr_destroy(XDR *xdrs);
65 A macro that invokes the destroy routine associated with the XDR
67 stream, xdrs. Destruction usually involves freeing private data
68 structures associated with the stream. Using xdrs after invok‐
69 ing xdr_destroy() is undefined.
70 bool_t xdr_double(XDR *xdrs, double *dp);
72 A filter primitive that translates between C double precision
74 numbers and their external representations. This routine re‐
75 turns one if it succeeds, zero otherwise.
76 bool_t xdr_enum(XDR *xdrs, enum_t *ep);
78 A filter primitive that translates between C enums (actually in‐
80 tegers) and their external representations. This routine re‐
81 turns one if it succeeds, zero otherwise.
82 bool_t xdr_float(XDR *xdrs, float *fp);
84 A filter primitive that translates between C floats and their
86 external representations. This routine returns one if it suc‐
87 ceeds, zero otherwise.
88 void xdr_free(xdrproc_t proc, char *objp);
90 Generic freeing routine. The first argument is the XDR routine
92 for the object being freed. The second argument is a pointer to
93 the object itself. Note: the pointer passed to this routine is
94 not freed, but what it points to is freed (recursively).
95 unsigned int xdr_getpos(XDR *xdrs);
97 A macro that invokes the get-position routine associated with
99 the XDR stream, xdrs. The routine returns an unsigned integer,
100 which indicates the position of the XDR byte stream. A desir‐
101 able feature of XDR streams is that simple arithmetic works with
102 this number, although the XDR stream instances need not guaran‐
103 tee this.
104 long *xdr_inline(XDR *xdrs, int len);
106 A macro that invokes the inline routine associated with the XDR
108 stream, xdrs. The routine returns a pointer to a contiguous
109 piece of the stream's buffer; len is the byte length of the de‐
110 sired buffer. Note: pointer is cast to long *.
111 Warning: xdr_inline() may return NULL (0) if it cannot allocate
113 a contiguous piece of a buffer. Therefore the behavior may vary
114 among stream instances; it exists for the sake of efficiency.
115 bool_t xdr_int(XDR *xdrs, int *ip);
117 A filter primitive that translates between C integers and their
119 external representations. This routine returns one if it suc‐
120 ceeds, zero otherwise.
121 bool_t xdr_long(XDR *xdrs, long *lp);
123 A filter primitive that translates between C long integers and
125 their external representations. This routine returns one if it
126 succeeds, zero otherwise.
127 void xdrmem_create(XDR *xdrs, char *addr, unsigned int size,
129 enum xdr_op op);
130 This routine initializes the XDR stream object pointed to by
132 xdrs. The stream's data is written to, or read from, a chunk of
133 memory at location addr whose length is no more than size bytes
134 long. The op determines the direction of the XDR stream (either
135 XDR_ENCODE, XDR_DECODE, or XDR_FREE).
136 bool_t xdr_opaque(XDR *xdrs, char *cp, unsigned int cnt);
138 A filter primitive that translates between fixed size opaque
140 data and its external representation. The argument cp is the
141 address of the opaque object, and cnt is its size in bytes.
142 This routine returns one if it succeeds, zero otherwise.
143 bool_t xdr_pointer(XDR *xdrs, char **objpp,
145 unsigned int objsize, xdrproc_t xdrobj);
146 Like xdr_reference() except that it serializes null pointers,
148 whereas xdr_reference() does not. Thus, xdr_pointer() can rep‐
149 resent recursive data structures, such as binary trees or linked
150 lists.
151 void xdrrec_create(XDR *xdrs, unsigned int sendsize,
153 unsigned int recvsize, char *handle,
154 int (*readit)(char *, char *, int),
155 int (*writeit)(char *, char *, int));
156 This routine initializes the XDR stream object pointed to by
158 xdrs. The stream's data is written to a buffer of size send‐
159 size; a value of zero indicates the system should use a suitable
160 default. The stream's data is read from a buffer of size recv‐
161 size; it too can be set to a suitable default by passing a zero
162 value. When a stream's output buffer is full, writeit is
163 called. Similarly, when a stream's input buffer is empty, rea‐
164 dit is called. The behavior of these two routines is similar to
165 the system calls read(2) and write(2), except that handle is
166 passed to the former routines as the first argument. Note: the
167 XDR stream's op field must be set by the caller.
168 Warning: to read from an XDR stream created by this API, you'll
170 need to call xdrrec_skiprecord() first before calling any other
171 XDR APIs. This inserts additional bytes in the stream to pro‐
172 vide record boundary information. Also, XDR streams created
173 with different xdr*_create APIs are not compatible for the same
174 reason.
175 bool_t xdrrec_endofrecord(XDR *xdrs, int sendnow);
177 This routine can be invoked only on streams created by xdr‐
179 rec_create(). The data in the output buffer is marked as a com‐
180 pleted record, and the output buffer is optionally written out
181 if sendnow is nonzero. This routine returns one if it succeeds,
182 zero otherwise.
183 bool_t xdrrec_eof(XDR *xdrs);
185 This routine can be invoked only on streams created by xdr‐
187 rec_create(). After consuming the rest of the current record in
188 the stream, this routine returns one if the stream has no more
189 input, zero otherwise.
190 bool_t xdrrec_skiprecord(XDR *xdrs);
192 This routine can be invoked only on streams created by xdr‐
194 rec_create(). It tells the XDR implementation that the rest of
195 the current record in the stream's input buffer should be dis‐
196 carded. This routine returns one if it succeeds, zero other‐
197 wise.
198 bool_t xdr_reference(XDR *xdrs, char **pp, unsigned int size,
200 xdrproc_t proc);
201 A primitive that provides pointer chasing within structures.
203 The argument pp is the address of the pointer; size is the
204 sizeof the structure that *pp points to; and proc is an XDR pro‐
205 cedure that filters the structure between its C form and its ex‐
206 ternal representation. This routine returns one if it succeeds,
207 zero otherwise.
208 Warning: this routine does not understand null pointers. Use
210 xdr_pointer() instead.
211 xdr_setpos(XDR *xdrs, unsigned int pos);
213 A macro that invokes the set position routine associated with
215 the XDR stream xdrs. The argument pos is a position value ob‐
216 tained from xdr_getpos(). This routine returns one if the XDR
217 stream could be repositioned, and zero otherwise.
218 Warning: it is difficult to reposition some types of XDR
220 streams, so this routine may fail with one type of stream and
221 succeed with another.
222 bool_t xdr_short(XDR *xdrs, short *sp);
224 A filter primitive that translates between C short integers and
226 their external representations. This routine returns one if it
227 succeeds, zero otherwise.
228 void xdrstdio_create(XDR *xdrs, FILE *file, enum xdr_op op);
230 This routine initializes the XDR stream object pointed to by
232 xdrs. The XDR stream data is written to, or read from, the
233 stdio stream file. The argument op determines the direction of
234 the XDR stream (either XDR_ENCODE, XDR_DECODE, or XDR_FREE).
235 Warning: the destroy routine associated with such XDR streams
237 calls fflush(3) on the file stream, but never fclose(3).
238 bool_t xdr_string(XDR *xdrs, char **sp, unsigned int maxsize);
240 A filter primitive that translates between C strings and their
242 corresponding external representations. Strings cannot be
243 longer than maxsize. Note: sp is the address of the string's
244 pointer. This routine returns one if it succeeds, zero other‐
245 wise.
246 bool_t xdr_u_char(XDR *xdrs, unsigned char *ucp);
248 A filter primitive that translates between unsigned C characters
250 and their external representations. This routine returns one if
251 it succeeds, zero otherwise.
252 bool_t xdr_u_int(XDR *xdrs, unsigned int *up);
254 A filter primitive that translates between C unsigned integers
256 and their external representations. This routine returns one if
257 it succeeds, zero otherwise.
258 bool_t xdr_u_long(XDR *xdrs, unsigned long *ulp);
260 A filter primitive that translates between C unsigned long inte‐
262 gers and their external representations. This routine returns
263 one if it succeeds, zero otherwise.
264 bool_t xdr_u_short(XDR *xdrs, unsigned short *usp);
266 A filter primitive that translates between C unsigned short in‐
268 tegers and their external representations. This routine returns
269 one if it succeeds, zero otherwise.
270 bool_t xdr_union(XDR *xdrs, enum_t *dscmp, char *unp,
272 const struct xdr_discrim *choices,
273 xdrproc_t defaultarm); /* may equal NULL */
274 A filter primitive that translates between a discriminated C
276 union and its corresponding external representation. It first
277 translates the discriminant of the union located at dscmp. This
278 discriminant is always an enum_t. Next the union located at unp
279 is translated. The argument choices is a pointer to an array of
280 xdr_discrim() structures. Each structure contains an ordered
281 pair of [value,proc]. If the union's discriminant is equal to
282 the associated value, then the proc is called to translate the
283 union. The end of the xdr_discrim() structure array is denoted
284 by a routine of value NULL. If the discriminant is not found in
285 the choices array, then the defaultarm procedure is called (if
286 it is not NULL). Returns one if it succeeds, zero otherwise.
287 bool_t xdr_vector(XDR *xdrs, char *arrp, unsigned int size,
289 unsigned int elsize, xdrproc_t elproc);
290 A filter primitive that translates between fixed-length arrays
292 and their corresponding external representations. The argument
293 arrp is the address of the pointer to the array, while size is
294 the element count of the array. The argument elsize is the
295 sizeof each of the array's elements, and elproc is an XDR filter
296 that translates between the array elements' C form, and their
297 external representation. This routine returns one if it suc‐
298 ceeds, zero otherwise.
299 bool_t xdr_void(void);
301 This routine always returns one. It may be passed to RPC rou‐
303 tines that require a function argument, where nothing is to be
304 done.
305 bool_t xdr_wrapstring(XDR *xdrs, char **sp);
307 A primitive that calls xdr_string(xdrs, sp,MAXUN.UNSIGNED );
309 where MAXUN.UNSIGNED is the maximum value of an unsigned inte‐
310 ger. xdr_wrapstring() is handy because the RPC package passes a
311 maximum of two XDR routines as arguments, and xdr_string(), one
312 of the most frequently used primitives, requires three. Returns
313 one if it succeeds, zero otherwise.
314
316 For an explanation of the terms used in this section, see at‐
317 tributes(7).
318 ┌────────────────────────────────────────────┬───────────────┬─────────┐
320 │Interface │ Attribute │ Value │
321 ├────────────────────────────────────────────┼───────────────┼─────────┤
322 │xdr_array(), xdr_bool(), xdr_bytes(), │ Thread safety │ MT-Safe │
323 │xdr_char(), xdr_destroy(), xdr_double(), │ │ │
324 │xdr_enum(), xdr_float(), xdr_free(), │ │ │
325 │xdr_getpos(), xdr_inline(), xdr_int(), │ │ │
326 │xdr_long(), xdrmem_create(), xdr_opaque(), │ │ │
327 │xdr_pointer(), xdrrec_create(), │ │ │
328 │xdrrec_eof(), xdrrec_endofrecord(), │ │ │
329 │xdrrec_skiprecord(), xdr_reference(), │ │ │
330 │xdr_setpos(), xdr_short(), │ │ │
331 │xdrstdio_create(), xdr_string(), │ │ │
332 │xdr_u_char(), xdr_u_int(), xdr_u_long(), │ │ │
333 │xdr_u_short(), xdr_union(), xdr_vector(), │ │ │
334 │xdr_void(), xdr_wrapstring() │ │ │
335 └────────────────────────────────────────────┴───────────────┴─────────┘
336
338 rpc(3)
339 The following manuals:
341 eXternal Data Representation Standard: Protocol Specification
342 eXternal Data Representation: Sun Technical Notes
343 XDR: External Data Representation Standard, RFC 1014, Sun Mi‐
344 crosystems, Inc., USC-ISI.
345Linux man-pages 6.04 2022-12-15 xdr(3)