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GETPROTOENT_R(3)           Linux Programmer's Manual          GETPROTOENT_R(3)

       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 pro-
       toent  structure  is  returned,  and  in  the  function  calling  signature and return value.  This manual page
       describes just the differences from the non-reentrant functions.

       Instead of returning a pointer to a statically allocated protoent structure as the function result, these func-
       tions 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 non-reen-
       trant 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; other-
       wise, *result is set to NULL.

       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 buflen).

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

       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)

       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

GNU                               2008-08-19                  GETPROTOENT_R(3)