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       getprotoent_r,  getprotobyname_r,  getprotobynumber_r  -  get  protocol
       entry (reentrant)


       #include <netdb.h>

       int getprotoent_r(struct protoent *result_buf, char *buf,
                       size_t buflen, struct protoent **result);

       int getprotobyname_r(const char *name,
                       struct protoent *result_buf, char *buf,
                       size_t buflen, struct protoent **result);

       int getprotobynumber_r(int proto,
                       struct protoent *result_buf, char *buf,
                       size_t buflen, struct protoent **result);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getprotoent_r(), getprotobyname_r(), getprotobynumber_r(): _BSD_SOURCE
       || _SVID_SOURCE


       The   getprotoent_r(),   getprotobyname_r(),  and  getprotobynumber_r()
       functions   are   the   reentrant   equivalents    of,    respectively,
       getprotoent(3),   getprotobyname(3),   and  getprotobynumber(3).   They
       differ in the way that the protoent structure is returned, and  in  the
       function   calling  signature  and  return  value.   This  manual  page
       describes just the differences from the nonreentrant functions.

       Instead of returning a  pointer  to  a  statically  allocated  protoent
       structure  as  the  function result, these functions copy the structure
       into the location pointed to by result_buf.

       The buf array is used to store the string  fields  pointed  to  by  the
       returned  protoent  structure.   (The  nonreentrant  functions allocate
       these strings in static storage.)  The size of this array is  specified
       in  buflen.  If buf is too small, the call fails with the error ERANGE,
       and the caller must try again with  a  larger  buffer.   (A  buffer  of
       length 1024 bytes should be sufficient for most applications.)

       If  the  function  call  successfully  obtains  a protocol record, then
       *result is set pointing to result_buf; otherwise,  *result  is  set  to


       On  success,  these  functions  return  0.   On error, a positive error
       number is returned.

       On error, record not found (getprotobyname_r(),  getprotobynumber_r()),
       or end of input (getprotoent_r()) result is set to NULL.


       ENOENT (getprotoent_r()) No more records in database.

       ERANGE buf is too small.  Try again with a larger buffer (and increased


       These functions are GNU extensions.  Functions with similar names exist
       on   some  other  systems,  though  typically  with  different  calling


       The program below uses  getprotobyname_r()  to  retrieve  the  protocol
       record for the protocol named in its first command-line argument.  If a
       second (integer) command-line argument is supplied, it is used  as  the
       initial  value  for  buflen; if getprotobyname_r() fails with the error
       ERANGE, the program retries with larger buffer  sizes.   The  following
       shell session shows a couple of sample runs:

           $ ./a.out tcp 1
           ERANGE! Retrying with larger buffer
           getprotobyname_r() returned: 0 (success)  (buflen=78)
           p_name=tcp; p_proto=6; aliases=TCP
           $ ./a.out xxx 1
           ERANGE! Retrying with larger buffer
           getprotobyname_r() returned: 0 (success)  (buflen=100)
           Call failed/record not found

   Program source

       #define _GNU_SOURCE
       #include <ctype.h>
       #include <netdb.h>
       #include <stdlib.h>
       #include <stdio.h>
       #include <errno.h>
       #include <string.h>

       #define MAX_BUF 10000

       main(int argc, char *argv[])
           int buflen, erange_cnt, s;
           struct protoent result_buf;
           struct protoent *result;
           char buf[MAX_BUF];
           char **p;

           if (argc < 2) {
               printf("Usage: %s proto-name [buflen]\n", argv[0]);

           buflen = 1024;
           if (argc > 2)
               buflen = atoi(argv[2]);

           if (buflen > MAX_BUF) {
               printf("Exceeded buffer limit (%d)\n", MAX_BUF);

           erange_cnt = 0;
           do {
               s = getprotobyname_r(argv[1], &result_buf,
                            buf, buflen, &result);
               if (s == ERANGE) {
                   if (erange_cnt == 0)
                       printf("ERANGE! Retrying with larger buffer\n");

                   /* Increment a byte at a time so we can see exactly
                      what size buffer was required */


                   if (buflen > MAX_BUF) {
                       printf("Exceeded buffer limit (%d)\n", MAX_BUF);
           } while (s == ERANGE);

           printf("getprotobyname_r() returned: %s  (buflen=%d)\n",
                   (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
                   strerror(s), buflen);

           if (s != 0 || result == NULL) {
               printf("Call failed/record not found\n");

           printf("p_name=%s; p_proto=%d; aliases=",
                       result_buf.p_name, result_buf.p_proto);
           for (p = result_buf.p_aliases; *p != NULL; p++)
               printf("%s ", *p);



       getprotoent(3), protocols(5)


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