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GETSERVENT_R(3) | Linux Programmer's Manual | GETSERVENT_R(3) |
NAME¶
getservent_r, getservbyname_r, getservbyport_r - get service entry (reentrant)SYNOPSIS¶
#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)):
_BSD_SOURCE || _SVID_SOURCE
DESCRIPTION¶
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.RETURN VALUE¶
On success, these functions return 0. On error, they return one of the positive error numbers listed in errors.ERRORS¶
- ENOENT
- (getservent_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 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 int 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]); exit(EXIT_FAILURE); } 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); exit(EXIT_FAILURE); } 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"); 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("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"); exit(EXIT_FAILURE); } printf("s_name=%s; s_proto=%s; s_port=%d; aliases=", result_buf.s_name, result_buf.s_proto, ntohs(result_buf.s_port)); for (p = result_buf.s_aliases; *p != NULL; p++) printf("%s ", *p); printf("\n"); exit(EXIT_SUCCESS); }
SEE ALSO¶
getservent(3), services(5)COLOPHON¶
This page is part of release 3.44 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/.2010-09-10 | GNU |