在这个过程中，存储char*会在某个地方遭到破坏

Storing char* gets clobbered somewhere along the way

本文关键字：方遭 过程中 存储 char      更新时间：2023-10-16

我有以下事件序列:

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++;
}

我不知道我在哪里复制/破坏了我的payload内存。有人发现我漏掉了什么吗?

这一行似乎是罪魁祸首，

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

打印本行前bytes的值

c++ 11使用自动内存管理的例子:

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

memcpy(pld, &payload, sz);

我猜你想要这个…

payload = pld

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