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       getservent_r, getservbyname_r, getservbyport_r - get service entry (reentrant)


       #include <netdb.h>

       int getservent_r(struct servent *result_buf, char *buf,
                       size_t buflen, struct servent **result);

       int getservbyname_r(const char *name, const char *proto,
                       struct servent *result_buf, char *buf,
                       size_t buflen, struct servent **result);

       int getservbyport_r(int port, const char *proto,
                       struct servent *result_buf, char *buf,
                       size_t buflen, struct servent **result);

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

       getservent_r(), getservbyname_r(), getservbyport_r():
           _BSD_SOURCE || _SVID_SOURCE


       The  getservent_r(),  getservbyname_r(), and getservbyport_r() functions are the reentrant
       equivalents of, respectively, getservent(3), getservbyname(3), and getservbyport(3).  They
       differ  in  the  way  that  the servent 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 servent 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  servent
       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 service 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  (getservbyname_r(),  getservbyport_r()),  or  end  of  input
       (getservent_r()) result is set to NULL.


       ENOENT (getservent_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          │
       │getservent_r(),    │ Thread safety │ MT-Safe locale │
       │getservbyname_r(), │               │                │
       │getservbyport_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 getservbyport_r() to retrieve the service record for the  port  and
       protocol  named  in  its  first  command-line argument.  If a third (integer) command-line
       argument is supplied, it is used as the initial value  for  buflen;  if  getservbyport_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 7 tcp 1
           ERANGE! Retrying with larger buffer
           getservbyport_r() returned: 0 (success)  (buflen=87)
           s_name=echo; s_proto=tcp; s_port=7; aliases=
           $ ./a.out 77777 tcp
           getservbyport_r() returned: 0 (success)  (buflen=1024)
           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, port, s;
           struct servent result_buf;
           struct servent *result;
           char buf[MAX_BUF];
           char *protop;
           char **p;

           if (argc < 3) {
               printf("Usage: %s port-num proto-name [buflen]\n", argv[0]);

           port = htons(atoi(argv[1]));
           protop = (strcmp(argv[2], "null") == 0 ||
                     strcmp(argv[2], "NULL") == 0) ?  NULL : argv[2];

           buflen = 1024;
           if (argc > 3)
               buflen = atoi(argv[3]);

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

           erange_cnt = 0;
           do {
               s = getservbyport_r(port, protop, &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("getservbyport_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("s_name=%s; s_proto=%s; s_port=%d; aliases=",
                       result_buf.s_name, result_buf.s_proto,
           for (p = result_buf.s_aliases; *p != NULL; p++)
               printf("%s ", *p);



       getservent(3), services(5)


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