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():
           _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

       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 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).

CONFORMING TO

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

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 3.54 of the Linux man-pages project.  A description of the project, and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.