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


       #include <netdb.h>

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

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

       getprotoent_r(), getprotobyname_r(), getprotobynumber_r():
           Since glibc 2.19:
           Glibc 2.19 and earlier:
               _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

       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.


       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.


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

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


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue          │
       │getprotoent_r(), getprotobyname_r(),                    │ Thread safety │ MT-Safe locale │
       │getprotobynumber_r()                                    │               │                │


       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];

           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 (char **p = result_buf.p_aliases; *p != NULL; p++)
               printf("%s ", *p);



       getprotoent(3), protocols(5)


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