getprotobynumber_r

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

NAME
       getprotoent_r,  getprotobyname_r, getprotobynumber_r - get protocol en-
       try (reentrant)

SYNOPSIS
       #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():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       The getprotoent_r(), getprotobyname_r(), and getprotobynumber_r() func-
       tions  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  dif-
       ferences 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 re-
       turned protoent structure.  (The nonreentrant functions allocate  these
       strings in static storage.)  The size of this array is specified in bu-
       flen.  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  *re-
       sult is set pointing to result_buf; otherwise, *result is set to NULL.

RETURN VALUE
       On success, these functions return 0.  On error, they return one of the
       positive error numbers listed in ERRORS.

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

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

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

ATTRIBUTES
       For an  explanation  of  the  terms  used  in  this  section,  see  at-
       tributes(7).

       +---------------------+---------------+----------------+
       |Interface            | Attribute     | Value          |
       +---------------------+---------------+----------------+
       |getprotoent_r(),     | Thread safety | MT-Safe locale |
       |getprotobyname_r(),  |               |                |
       |getprotobynumber_r() |               |                |
       +---------------------+---------------+----------------+

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

EXAMPLE
       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

       int
       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]);
               exit(EXIT_FAILURE);
           }

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

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

           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");
                   erange_cnt++;

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

                   buflen++;

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

           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);
           printf("\n");

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       getprotoent(3), protocols(5)

COLOPHON
       This page is part of release 5.05 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

GNU                               2019-03-06                  GETPROTOENT_R(3)