IF_NAMETOINDEX(3) | Library Functions Manual | IF_NAMETOINDEX(3)

# NAME

`if_nametoindex`, `if_indextoname`, `if_nameindex`, `if_freenameindex` —
provide mappings between interface names and indexes

# SYNOPSIS

`#include <net/if.h>`

unsigned int
`if_nametoindex`(const char *ifname);

char *
`if_indextoname`(unsigned int ifindex, char *ifname);

struct if_nameindex *
`if_nameindex`(void);

void
`if_freenameindex`(struct if_nameindex *ptr);

# DESCRIPTION

The `if_nametoindex`() function maps the interface name specified in ifname to its corresponding index. If the specified interface does not exist, it returns 0.

The `if_indextoname`() function maps the interface index specified in ifindex to it corresponding name, which is copied into the buffer pointed to by ifname, which must be of at least IFNAMSIZ bytes. This pointer is also the return value of the function. If there is no interface corresponding to the specified index, NULL is returned.

The `if_nameindex`() function returns an array of `if_nameindex` structures, one structure per interface, as defined in the include file `<net/if.h>`. The `if_nameindex` structure contains at least the following entries:

        unsigned int   if_index;  /* 1, 2, ... */
        char          *if_name;   /* null terminated name: "le0", ... */

The end of the array of structures is indicated by a structure with an `if_index` of 0 and an `if_name` of NULL. A NULL pointer is returned upon an error.

The `if_freenameindex`() function frees the dynamic memory that was allocated by `if_nameindex`().

# RETURN VALUES

Upon successful completion, `if_nametoindex`() returns the index number of the interface. If the interface is not found, a value of 0 is returned and errno is set to `ENXIO`. A value of 0 is also returned if an error occurs while retrieving the list of interfaces via getifaddrs(3).

Upon successful completion, `if_indextoname`() returns ifname. If the interface is not found, a NULL pointer is returned and errno is set to `ENXIO`. A NULL pointer is also returned if an error occurs while retrieving the list of interfaces via getifaddrs(3).

The `if_nameindex`() returns a NULL pointer if an error occurs while retrieving the list of interfaces via getifaddrs(3), or if sufficient memory cannot be allocated.

# SEE ALSO

getifaddrs(3), networking(4)

# STANDARDS

The `if_nametoindex`(), `if_indextoname`(), `if_nameindex`(), and `if_freenameindex`() functions conform to IEEE Std 1003.1-2001 (“POSIX.1”), X/Open Networking Services Issue 5.2 (“XNS5.2”), and RFC 3493.

# HISTORY

The implementation first appeared in BSD/OS.

March 11, 2005 | NetBSD 9.0