使用 gdb 检查对象时获取不同的值
我正在使用 gdb 来调试因分段错误而终止的 C++ 程序。查看堆栈，前几帧是：
#0 0x0041c496 in cDefaultList::doInsert (this=0x9c69708, obj=0x9c69348) at cdefaultlist.cc:119
#1 0x0041c86c in cDefaultList::take (this=0x9c69708, obj=0x9c69348) at cdefaultlist.cc:189
#2 0x0043bd9c in cPacket::encapsulate (this=0x9c69708, msg=0x9c69348) at cmessage.cc:589
#3 0x08448861 in MobIPv6mn::handleMessage (this=0x96d3350, msg=0x9c69348) at src/networklayer/numbatIPv6/mip6.cc:170
#4 0x0046069c in cSimulation::doOneEvent (this=0x87f3318, mod=0x96d3350) at csimulation.cc:627
#5 0x0015ecdf in Tkenv::doRunSimulation (this=0x87f3110) at tkenv.cc:529
#6 0x0015e899 in Tkenv::runSimulation (this=0x87f3110, mode=2, until_time=..., until_eventnum=0, until_msg=0x0, until_module=0x0) at tkenv.cc:402
#7 0x00168f10 in run_cmd (interp=0x8842e48, argc=2, argv=0xbfffcb00) at tkcmd.cc:430
所以我这样做：
frame 3
然后想用 print * (IPv6 *) msg 检查“msg”，因为这就是 msg 的类型。好吧，当我查看 msg 的 Ipv6 特定字段时，我总是得到完全不同的值，例如：
srcIP_var = {addr = "\000\000\000\000\000\000i\000\000\000 \001\000\000\000\001"}, dstIP_var = { addr = "\000\000H\223\306\t\000\000\000\000\000\000\000\000\000"}, BindingUpdate_var = false, BindingAck_var = false, Dhcpv6Relay_var = false}
或
srcIP_var = {addr = "\000\000\000\000\000\000)\000\000\000\020\264K\000\020\264"}, dstIP_var = {addr = "\346 \t:SCALEXP_UNIN"}，BindingUpdate_var = 73， BindingAck_var = 84，Dhcpv6Relay_var = 73}
甚至：
srcIP_var = {addr = "\000\000\000\000\000\000\061\000\000\000\030\264K\000 \030\264"}, dstIP_var = { addr = "K\000\a\350N\v\304\350N\v\001\000\000\000\001"}，BindingUpdate_var = false，BindingAck_var = false，Dhcpv6Relay_var = false} 这是为什么
呢？这是否意味着数据包实际上不是我尝试将其转换为的类型？
多谢！
I'm using gdb to debug a c++ program which terminated with a segmentation fault. Looking at the stack, the first few frames are:
#0 0x0041c496 in cDefaultList::doInsert (this=0x9c69708, obj=0x9c69348) at cdefaultlist.cc:119
#1 0x0041c86c in cDefaultList::take (this=0x9c69708, obj=0x9c69348) at cdefaultlist.cc:189
#2 0x0043bd9c in cPacket::encapsulate (this=0x9c69708, msg=0x9c69348) at cmessage.cc:589
#3 0x08448861 in MobIPv6mn::handleMessage (this=0x96d3350, msg=0x9c69348) at src/networklayer/numbatIPv6/mip6.cc:170
#4 0x0046069c in cSimulation::doOneEvent (this=0x87f3318, mod=0x96d3350) at csimulation.cc:627
#5 0x0015ecdf in Tkenv::doRunSimulation (this=0x87f3110) at tkenv.cc:529
#6 0x0015e899 in Tkenv::runSimulation (this=0x87f3110, mode=2, until_time=..., until_eventnum=0, until_msg=0x0, until_module=0x0) at tkenv.cc:402
#7 0x00168f10 in run_cmd (interp=0x8842e48, argc=2, argv=0xbfffcb00) at tkcmd.cc:430
So I do:
frame 3
and later want to inspect "msg" with print * (IPv6 *) msg, because that's what the type of msg should be. Well, when I look at the Ipv6-specific fields of msg, I always get completely different values, like:
srcIP_var = {addr = "\000\000\000\000\000\000i\000\000\000\001\000\000\000\001"}, dstIP_var = {
addr = "\000\000H\223\306\t\000\000\000\000\000\000\000\000\000"}, BindingUpdate_var = false, BindingAck_var = false, Dhcpv6Relay_var = false}
or
srcIP_var = {addr = "\000\000\000\000\000\000)\000\000\000\020\264K\000\020\264"}, dstIP_var = {addr = "\346\t:SCALEEXP_UNIN"}, BindingUpdate_var = 73,
BindingAck_var = 84, Dhcpv6Relay_var = 73}
or even:
srcIP_var = {addr = "\000\000\000\000\000\000\061\000\000\000\030\264K\000\030\264"}, dstIP_var = {
addr = "K\000\a\350N\v\304\350N\v\001\000\000\000\001"}, BindingUpdate_var = false, BindingAck_var = false, Dhcpv6Relay_var = false}
Why is that? Does that mean the packet is not really of the type I tried to cast it to?
Thanks a lot!
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您确定您不只是查看未初始化（或释放然后重新使用）的内存吗？这也可以解释为什么你的代码崩溃了。
Are you sure you're not just looking at uninitialized (or freed and then re-used) memory? That could explain why your code is crashing as well.