1GETPROTOENT_R(3) Linux Programmer's Manual GETPROTOENT_R(3)
2
6 getprotoent_r, getprotobyname_r, getprotobynumber_r - get protocol
7 entry (reentrant)
8
10 #include <netdb.h>
11 int getprotoent_r(struct protoent *result_buf, char *buf,
13 size_t buflen, struct protoent **result);
14 int getprotobyname_r(const char *name,
16 struct protoent *result_buf, char *buf,
17 size_t buflen, struct protoent **result);
18 int getprotobynumber_r(int proto,
20 struct protoent *result_buf, char *buf,
21 size_t buflen, struct protoent **result);
22 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24 getprotoent_r(), getprotobyname_r(), getprotobynumber_r():
26 Since glibc 2.19:
27 _DEFAULT_SOURCE
28 Glibc 2.19 and earlier:
29 _BSD_SOURCE || _SVID_SOURCE
30
32 The getprotoent_r(), getprotobyname_r(), and getprotobynumber_r() func‐
33 tions are the reentrant equivalents of, respectively, getprotoent(3),
34 getprotobyname(3), and getprotobynumber(3). They differ in the way
35 that the protoent structure is returned, and in the function calling
36 signature and return value. This manual page describes just the dif‐
37 ferences from the nonreentrant functions.
38 Instead of returning a pointer to a statically allocated protoent
40 structure as the function result, these functions copy the structure
41 into the location pointed to by result_buf.
42 The buf array is used to store the string fields pointed to by the
44 returned protoent structure. (The nonreentrant functions allocate
45 these strings in static storage.) The size of this array is specified
46 in buflen. If buf is too small, the call fails with the error ERANGE,
47 and the caller must try again with a larger buffer. (A buffer of
48 length 1024 bytes should be sufficient for most applications.)
49 If the function call successfully obtains a protocol record, then
51 *result is set pointing to result_buf; otherwise, *result is set to
52 NULL.
53
55 On success, these functions return 0. On error, they return one of the
56 positive error numbers listed in ERRORS.
57 On error, record not found (getprotobyname_r(), getprotobynumber_r()),
59 or end of input (getprotoent_r()) result is set to NULL.
60
62 ENOENT (getprotoent_r()) No more records in database.
63 ERANGE buf is too small. Try again with a larger buffer (and increased
65 buflen).
66
68 For an explanation of the terms used in this section, see
69 attributes(7).
70 ┌─────────────────────┬───────────────┬────────────────┐
72 │Interface │ Attribute │ Value │
73 ├─────────────────────┼───────────────┼────────────────┤
74 │getprotoent_r(), │ Thread safety │ MT-Safe locale │
75 │getprotobyname_r(), │ │ │
76 │getprotobynumber_r() │ │ │
77 └─────────────────────┴───────────────┴────────────────┘
78
80 These functions are GNU extensions. Functions with similar names exist
81 on some other systems, though typically with different calling signa‐
82 tures.
83
85 The program below uses getprotobyname_r() to retrieve the protocol
86 record for the protocol named in its first command-line argument. If a
87 second (integer) command-line argument is supplied, it is used as the
88 initial value for buflen; if getprotobyname_r() fails with the error
89 ERANGE, the program retries with larger buffer sizes. The following
90 shell session shows a couple of sample runs:
91 $ ./a.out tcp 1
93 ERANGE! Retrying with larger buffer
94 getprotobyname_r() returned: 0 (success) (buflen=78)
95 p_name=tcp; p_proto=6; aliases=TCP
96 $ ./a.out xxx 1
97 ERANGE! Retrying with larger buffer
98 getprotobyname_r() returned: 0 (success) (buflen=100)
99 Call failed/record not found
100 Program source
102 #define _GNU_SOURCE
104 #include <ctype.h>
105 #include <netdb.h>
106 #include <stdlib.h>
107 #include <stdio.h>
108 #include <errno.h>
109 #include <string.h>
110 #define MAX_BUF 10000
112 int
114 main(int argc, char *argv[])
115 {
116 int buflen, erange_cnt, s;
117 struct protoent result_buf;
118 struct protoent *result;
119 char buf[MAX_BUF];
120 char **p;
121 if (argc < 2) {
123 printf("Usage: %s proto-name [buflen]\n", argv[0]);
124 exit(EXIT_FAILURE);
125 }
126 buflen = 1024;
128 if (argc > 2)
129 buflen = atoi(argv[2]);
130 if (buflen > MAX_BUF) {
132 printf("Exceeded buffer limit (%d)\n", MAX_BUF);
133 exit(EXIT_FAILURE);
134 }
135 erange_cnt = 0;
137 do {
138 s = getprotobyname_r(argv[1], &result_buf,
139 buf, buflen, &result);
140 if (s == ERANGE) {
141 if (erange_cnt == 0)
142 printf("ERANGE! Retrying with larger buffer\n");
143 erange_cnt++;
144 /* Increment a byte at a time so we can see exactly
146 what size buffer was required */
147 buflen++;
149 if (buflen > MAX_BUF) {
151 printf("Exceeded buffer limit (%d)\n", MAX_BUF);
152 exit(EXIT_FAILURE);
153 }
154 }
155 } while (s == ERANGE);
156 printf("getprotobyname_r() returned: %s (buflen=%d)\n",
158 (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
159 strerror(s), buflen);
160 if (s != 0 || result == NULL) {
162 printf("Call failed/record not found\n");
163 exit(EXIT_FAILURE);
164 }
165 printf("p_name=%s; p_proto=%d; aliases=",
167 result_buf.p_name, result_buf.p_proto);
168 for (p = result_buf.p_aliases; *p != NULL; p++)
169 printf("%s ", *p);
170 printf("\n");
171 exit(EXIT_SUCCESS);
173 }
174
176 getprotoent(3), protocols(5)
177
179 This page is part of release 5.02 of the Linux man-pages project. A
180 description of the project, information about reporting bugs, and the
181 latest version of this page, can be found at
182 https://www.kernel.org/doc/man-pages/.
183GNU 2019-03-06 GETPROTOENT_R(3)