Linxu的struct ifaddrs 与getifaddrs（）函数

来自man函数手册中的介绍：

1，关于struct ifaddrs的说明：

2，关于getifaddrs()

The getifaddrs() function creates a linked list of structures describing the network interfaces of the local system, and stores the address of the first
item of the list in *ifap.  
The list consists of ifaddrs structures, defined as follows:

       The ifa_next field contains a pointer to the next structure on the list, or
       NULL if this is the last item of the list.

       The ifa_name points to the null-terminated interface name.

       The ifa_flags field contains the interface flags

       The ifa_addr field points to a structure containing the interface address.

       The ifa_netmask field points to a structure containing the netmask associated with ifa_addr, if applicable for the address family.

       Depending on whether the bit IFF_BROADCAST or IFF_POINTOPOINT is set in ifa_flags (only one can be set at a time), either ifa_broadaddr will contain the broadcast address associated with ifa_addr (if applicable for the address family) or ifa_dstaddr will contain the destination address of the point-to-point interface.

       The ifa_data field points to a buffer containing address-family-specific data;this field may be NULL if there is no such data for this interface.

返回值：
On success, getifaddrs() returns zero; on error, -1 is returned, and errno is set appropriately.

3，注意：
       The data returned by getifaddrs() is dynamically allocated and should be freed using freeifaddrs() when no longer needed.

4,  man中的实例代码：