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

       For an explanation of the terms used in this section, see attributes(7).
       ┌──────────────────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │ Interface                                                            │ Attribute     │ Value          │
       ├──────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │ getprotoent_r(), getprotobyname_r(), getprotobynumber_r()            │ Thread safety │ MT-Safe locale │
       └──────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┘

       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.

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

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

       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.outtcp1
           ERANGE! Retrying with larger buffer
           getprotobyname_r() returned: 0 (success)  (buflen=78)
           p_name=tcp; p_proto=6; aliases=TCP
           $ ./a.outxxx1
           ERANGE! Retrying with larger buffer
           getprotobyname_r() returned: 0 (success)  (buflen=100)
           Call failed/record not found

   Programsource

       #define _GNU_SOURCE
       #include <ctype.h>
       #include <errno.h>
       #include <netdb.h>
       #include <stdio.h>
       #include <stdlib.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];

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

           exit(EXIT_SUCCESS);
       }

       Standard C library (libc, -lc)

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

       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.

getprotoent(3), protocols(5)

Linux man-pages 6.9.1                              2024-06-15                                   getprotoent_r(3)

       GNU.

#include<netdb.h>intgetprotoent_r(structprotoent*restrictresult_buf,charbuf[restrict.buflen],size_tbuflen,structprotoent**restrictresult);intgetprotobyname_r(constchar*restrictname,structprotoent*restrictresult_buf,charbuf[restrict.buflen],size_tbuflen,structprotoent**restrictresult);intgetprotobynumber_r(intproto,structprotoent*restrictresult_buf,charbuf[restrict.buflen],size_tbuflen,structprotoent**restrictresult);

   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

       Functions with similar names exist on  some  other  systems,  though  typically  with  different  calling
       signatures.