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26 .TH IF_NAMEINDEX 3 2021-03-22 "GNU" "Linux Programmer's Manual"
28 if_nameindex, if_freenameindex \- get network interface names and indexes
31 .B #include <net/if.h>
33 .BI "struct if_nameindex *if_nameindex(" void );
34 .BI "void if_freenameindex(struct if_nameindex *" "ptr" );
39 function returns an array of
41 structures, each containing information
42 about one of the network interfaces on the local system.
45 structure contains at least the following entries:
49 unsigned int if_index; /* Index of interface (1, 2, ...) */
50 char *if_name; /* Null\-terminated name ("eth0", etc.) */
56 field contains the interface index.
59 field points to the null-terminated interface name.
60 The end of the array is indicated by entry with
66 The data structure returned by
68 is dynamically allocated and should be freed using
69 .BR if_freenameindex ()
70 when no longer needed.
74 returns pointer to the array;
75 on error, NULL is returned, and
77 is set to indicate the error.
85 Insufficient resources available.
88 may also fail for any of the errors specified for
100 function first appeared in glibc 2.1, but before glibc 2.3.4,
101 the implementation supported only interfaces with IPv4 addresses.
102 Support of interfaces that don't have IPv4 addresses is available only
103 on kernels that support netlink.
105 For an explanation of the terms used in this section, see
113 Interface Attribute Value
116 .BR if_freenameindex ()
117 T} Thread safety MT-Safe
123 POSIX.1-2001, POSIX.1-2008, RFC\ 3493.
125 This function first appeared in BSDi.
127 The program below demonstrates the use of the functions described
129 An example of the output this program might produce is the following:
147 main(int argc, char *argv[])
149 struct if_nameindex *if_ni, *i;
151 if_ni = if_nameindex();
153 perror("if_nameindex");
157 for (i = if_ni; ! (i\->if_index == 0 && i\->if_name == NULL); i++)
158 printf("%u: %s\en", i\->if_index, i\->if_name);
160 if_freenameindex(if_ni);
169 .BR if_indextoname (3),
170 .BR if_nametoindex (3),