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

NAME

     getprotoent_r,  getprotobyname_r,  getprotobynumber_r  -  get  protocol
     entry (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
     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
     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
     attributes(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  getprotoby-
         name_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); }