Question

我有以下一系列事件：

for(int i = 0; i < 4; i++)
{
    int seqNum;
    int ackNum;
    int pldSize;
    char* payload = (char*)malloc(DEFINED_SIZE);

    //buffer updated each loop, assume:  140hello!
    Packet::decap(buffer, seqNum, ackNum, pldSize, payload);
    Packet p = Packet(seqNum, ackNum, pldSize, payload);
    dataMap.insert(pair<int,struct Packet>(seqNum, p)); 
}

...
struct Packet
{
   Packet(int,int,int,char*);
   int seqNum;
   int ackNum;  
   int payloadSize;
   char* payload;

   char* encap();
   static void decap(char* datagram, int & seqn, int & ackn, int & bytes, char* pyld);
};

void
Packet::decap(char* datagram, int & seqn, int & ackn, int & bytes, char* pyld)
{
    memcpy(&seqn, datagram, sizeof(int));
    memcpy(&ackn, &datagram[4], sizeof(int));
    memcpy(&bytes, &datagram[8], sizeof(int));
    memcpy(pyld, &datagram[12], bytes);
}

Packet::Packet(int seq, int ack, int sz, char* pld)
{
    seqNum = seq;
    ackNum = ack;
    payloadSize = sz;
    memcpy(pld, &payload, sz);
}

...

map<int, struct Packet>::iterator dataIter = dataMap.begin();


while(dataIter != dataMap.end())
{
    outfile.write(dataIter->second.payload, dataIter->second.payloadSize); //<<< Crash
    dataIter++;
}

我无法弄清楚我在哪一点上复制/破坏了我的payload记忆..有没有人看到我遗失的任何东西？

Answer 1

这一行似乎是罪魁祸首，

memcpy(pyld, &datagram[12], bytes);

在此行之前打印bytes的值。

Answer 2

使用自动内存管理的C ++ 11示例：

typedef std::array<char, DEFINED_SIZE> packet_t;
typedef std::shared_ptr<packet_t> shared_packet_t;

for(int i = 0; i < 4; i++)
{
    int seqNum;
    int ackNum;
    int pldSize;
    // memory allocated here as new packet_t() but owned by shared_packet_t
    shared_packet_t payload(new packet_t());

    //buffer updated each loop, assume:  140hello!
    Packet::decap(buffer, seqNum, ackNum, pldSize, payload);

    // a second reference to packet_t exists in p
    Packet p(seqNum, ackNum, pldSize, payload);

    // a third reference to packet_t exists in a new copy of p that was created
    // when pair<> was constructed
    dataMap.insert(pair<int,struct Packet>(seqNum, p)); 

    // payload and p are auto released here, but a reference to packet_t
    // still exists via the reference to Packet in pair<> in the dataMap
}

struct Packet
{
   Packet(int,int,int,shared_packet_t);
   int seqNum;
   int ackNum;  
   int payloadSize;
   shared_packet_t payload;

   char* encap();
   static void decap(char* datagram, int & seqn, int & ackn, int & bytes, shared_packet_t pyld);
};

void
Packet::decap(char* datagram, int & seqn, int & ackn, int & bytes, shared_packet_t pyld)
{
    memcpy(&seqn, datagram, sizeof(int));
    memcpy(&ackn, &datagram[4], sizeof(int));
    memcpy(&bytes, &datagram[8], sizeof(int));
    memcpy(pyld->data(), &datagram[12], bytes);
}

Packet::Packet(int seq, int ack, int sz, shared_packet_t pld)
:seqNum(seq), ackNum(ack), payloadSize(sz), payload(pld)
{
}

...

map<int, struct Packet>::iterator dataIter = dataMap.begin();


while(dataIter != dataMap.end())
{
    outfile.write(dataIter->second.payload->data(), dataIter->second.payloadSize);
    dataIter++;
}

应该用c ++ -std = c ++ 11

编译

Answer 3

memcpy(pld, &payload, sz);

我怀疑你想要这个...

payload = pld

存储char *会在整个过程中被破坏

3 个答案: