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NAME |LIBRARY |SYNOPSIS AND DESCRIPTION |ATTRIBUTES |SEE ALSO |COLOPHON | |
xdr(3) Library Functions Manualxdr(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 intbool_t;typedef typeof(bool_t (XDR *, void *, ...)) *xdrproc_t; For the declaration of theXDR type, see<rpc/xdr.h>.bool_t xdr_array(XDR *xdrs, char **arrp, unsigned int *sizep,unsigned intmaxsize, unsigned intelsize,xdrproc_telproc); A filter primitive that translates between variable-length arrays and their corresponding external representations. The argumentarrp is the address of the pointer to the array, whilesizep is the address of the element count of the array; this element count cannot exceedmaxsize. The argumentelsize is thesizeof each of the array's elements, andelproc 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 intmaxsize); A filter primitive that translates between counted byte strings and their external representations. The argumentsp is the address of the string pointer. The length of the string is located at addresssizep; strings cannot be longer thanmaxsize. 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 considerxdr_bytes(),xdr_opaque(), orxdr_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. Usingxdrs after invokingxdr_destroy() is undefined.bool_t xdr_double(XDR *xdrs, double *dp); A filter primitive that translates between Cdouble 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 Cenums (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 Cfloats and their external representations. This routine returns one if it succeeds, zero otherwise.void xdr_free(xdrproc_tproc, 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 isnot freed, but what it points tois 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, intlen); 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 tolong *. 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 Clong integers and their external representations. This routine returns one if it succeeds, zero otherwise.void xdrmem_create(XDR *xdrs, char *addr, unsigned intsize,enum xdr_opop); This routine initializes the XDR stream object pointed to byxdrs. The stream's data is written to, or read from, a chunk of memory at locationaddr whose length is no more thansize bytes long. Theop determines the direction of the XDR stream (eitherXDR_ENCODE,XDR_DECODE, orXDR_FREE).bool_t xdr_opaque(XDR *xdrs, char *cp, unsigned intcnt); A filter primitive that translates between fixed size opaque data and its external representation. The argumentcp is the address of the opaque object, andcnt is its size in bytes. This routine returns one if it succeeds, zero otherwise.bool_t xdr_pointer(XDR *xdrs, char **objpp,unsigned intobjsize, xdrproc_txdrobj); Likexdr_reference() except that it serializes null pointers, whereasxdr_reference() does not. Thus,xdr_pointer() can represent recursive data structures, such as binary trees or linked lists.void xdrrec_create(XDR *xdrs, unsigned intsendsize,unsigned intrecvsize, char *handle,typeof(int (char *, char *, int)) *readit,typeof(int (char *, char *, int)) *writeit); This routine initializes the XDR stream object pointed to byxdrs. The stream's data is written to a buffer of sizesendsize; a value of zero indicates the system should use a suitable default. The stream's data is read from a buffer of sizerecvsize; 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 callsread(2) andwrite(2), except thathandle is passed to the former routines as the first argument. Note: the XDR stream'sop field must be set by the caller. Warning: to read from an XDR stream created by this API, you'll need to callxdrrec_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 differentxdr*_createAPIs are not compatible for the same reason.bool_t xdrrec_endofrecord(XDR *xdrs, intsendnow); This routine can be invoked only on streams created byxdrrec_create(). The data in the output buffer is marked as a completed record, and the output buffer is optionally written out ifsendnow 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 byxdrrec_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 byxdrrec_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 intsize,xdrproc_tproc); A primitive that provides pointer chasing within structures. The argumentpp is the address of the pointer;size is thesizeof the structure that*pp points to; andproc 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. Usexdr_pointer() instead.xdr_setpos(XDR *xdrs, unsigned intpos); A macro that invokes the set position routine associated with the XDR streamxdrs. The argumentpos is a position value obtained fromxdr_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 Cshort integers and their external representations. This routine returns one if it succeeds, zero otherwise.void xdrstdio_create(XDR *xdrs, FILE *file, enum xdr_opop); This routine initializes the XDR stream object pointed to byxdrs. The XDR stream data is written to, or read from, thestdio streamfile. The argumentop determines the direction of the XDR stream (eitherXDR_ENCODE,XDR_DECODE, orXDR_FREE). Warning: the destroy routine associated with such XDR streams callsfflush(3) on thefile stream, but neverfclose(3).bool_t xdr_string(XDR *xdrs, char **sp, unsigned intmaxsize); A filter primitive that translates between C strings and their corresponding external representations. Strings cannot be longer thanmaxsize. 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 betweenunsigned 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 Cunsigned 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 Cunsigned 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 Cunsigned 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_tdefaultarm); /* may equal NULL */ A filter primitive that translates between a discriminated Cunion and its corresponding external representation. It first translates the discriminant of the union located atdscmp. This discriminant is always anenum_t. Next the union located atunp is translated. The argumentchoices is a pointer to an array ofxdr_discrim() structures. Each structure contains an ordered pair of [value,proc]. If the union's discriminant is equal to the associatedvalue, then theproc is called to translate the union. The end of thexdr_discrim() structure array is denoted by a routine of value NULL. If the discriminant is not found in thechoices array, then thedefaultarm procedure is called (if it is not NULL). Returns one if it succeeds, zero otherwise.bool_t xdr_vector(XDR *xdrs, char *arrp, unsigned intsize,unsigned intelsize, xdrproc_telproc); A filter primitive that translates between fixed-length arrays and their corresponding external representations. The argumentarrp is the address of the pointer to the array, whilesize is the element count of the array. The argumentelsize is thesizeof each of the array's elements, andelproc 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 callsxdr_string(xdrs, sp,MAXUN.UNSIGNED);whereMAXUN.UNSIGNEDis the maximum value of an unsigned integer.xdr_wrapstring() is handy because the RPC package passes a maximum of two XDR routines as arguments, andxdr_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, seeattributes(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 NotesXDR: External Data Representation Standard, RFC 1014, Sun Microsystems, Inc., USC-ISI.
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HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |