在LINUX下获取网卡信息&&getifaddrs的时候遇到了内存方面的问题&&struct socketaddr和struct socketaddr_in的区
在LINUX下获取网卡信息需要用到IOCTL或者getifaddrs
而我在用getifaddrs的时候遇到了内存方面的问题

先看相关定义:
==========

函数定义:
/* Create a linked list of `struct ifaddrs' structures, one for each
   network interface on the host machine.  If successful, store the
   list in *IFAP and return 0.  On errors, return -1 and set `errno'.

   The storage returned in *IFAP is allocated dynamically and can
   only be properly freed by passing it to `freeifaddrs'.  */
extern int getifaddrs (struct ifaddrs **__ifap) __THROW;

/* Reclaim the storage allocated by a previous `getifaddrs' call.  */
extern void freeifaddrs (struct ifaddrs *__ifa)  __THROW;
==============
此函数需要的结构体定义:

struct ifaddrs
{
  struct ifaddrs *ifa_next;     /* Pointer to the next structure.  */

  char *ifa_name;               /* Name of this network interface.  */
  unsigned int ifa_flags;       /* Flags as from SIOCGIFFLAGS ioctl.  */

  struct sockaddr *ifa_addr;    /* Network address of this interface.  */
  struct sockaddr *ifa_netmask; /* Netmask of this interface.  */
  union
  {
    /* At most one of the following two is valid.  If the IFF_BROADCAST
       bit is set in `ifa_flags', then `ifa_broadaddr' is valid.  If the
       IFF_POINTOPOINT bit is set, then `ifa_dstaddr' is valid.
       It is never the case that both these bits are set at once.  */
    struct sockaddr *ifu_broadaddr; /* Broadcast address of this interface. */
    struct sockaddr *ifu_dstaddr; /* Point-to-point destination address.  */
  } ifa_ifu;
  /* These very same macros are defined by <net/if.h> for `struct ifaddr'.
     So if they are defined already, the existing definitions will be fine.  */
# ifndef ifa_broadaddr
#  define ifa_broadaddr ifa_ifu.ifu_broadaddr
# endif
# ifndef ifa_dstaddr
#  define ifa_dstaddr   ifa_ifu.ifu_dstaddr
# endif

  void *ifa_data;               /* Address-specific data (may be unused).  */
};
=============
我在调用了getifaddrs()之后,正常地完成了需要的工作
但是最后如果用freeifaddrs,则出现运行时错误
*** glibc detected *** d: free(): invalid pointer: 0x0804a4d4 ***
======= Backtrace: =========
/lib/libc.so.6[0xb7eda911]
/lib/libc.so.6(__libc_free+0x84)[0xb7edbf84]
/lib/libc.so.6(freeifaddrs+0x1d)[0xb7f512dd]
d[0x8048989]
d[0x80486a5]
/lib/libc.so.6(__libc_start_main+0xdc)[0xb7e8c87c]
d[0x8048491]
======= Memory map: ========
08048000-08049000 r-xp 00000000 03:07 48637 /home/souldump/bin/d
08049000-0804a000 rw-p 00000000 03:07 48637 /home/souldump/bin/d
0804a000-0806b000 rw-p 0804a000 00:00 0 [heap]
b7d00000-b7d21000 rw-p b7d00000 00:00 0
b7d21000-b7e00000 ---p b7d21000 00:00 0
b7e76000-b7e77000 rw-p b7e76000 00:00 0
b7e77000-b7f90000 r-xp 00000000 03:05 16184 /lib/libc-2.4.so
b7f90000-b7f92000 r--p 00118000 03:05 16184 /lib/libc-2.4.so
b7f92000-b7f94000 rw-p 0011a000 03:05 16184 /lib/libc-2.4.so
b7f94000-b7f98000 rw-p b7f94000 00:00 0
b7fab000-b7fb5000 r-xp 00000000 03:05 20108 /lib/libgcc_s.so.1
b7fb5000-b7fb6000 rw-p 00009000 03:05 20108 /lib/libgcc_s.so.1
b7fb6000-b7fb7000 rw-p b7fb6000 00:00 0
b7fb7000-b7