当我push_back到向量时，析构函数被调用 [英] Destructor is called when I push_back to the vector

问题描述

我有这个类定义：

  class FlashStream 
 {
 public：
显式的FlashStream（const char * url，vector< uint8> * headers，vector< uint8> * data，void * ndata，void * notifyData = NULL，uint32 lastModified = NULL）; 
〜FlashStream（）; 
 private：
 NPStream _stream; 
 // ... 
} 
  

（ NPStream description ）

及其实现：

/ p>

  FlashStream :: FlashStream（const char * url，vector< uint8> * headers，vector< uint8> * data，void * ndata ，void * notifyData，uint32 lastModified）
 {
 // ... 
 memset（& _stream，0，sizeof（NPStream））; 
 
 _stream.headers = new char [data-> size（）]; 
 
 memcpy（（void *）_stream.headers，&（* data）[0]，data-> size（））; 
 // ... 
} 
 
 FlashStream ::〜FlashStream（）
 {
 // ... 
 if .headers）
 delete [] _stream.headers; 
 _stream.headers = NULL; 
 // ... 
} 
  

现在， ：

  // ... 
 vector< FlashStream> _streams; 
 // ... 
 _streams.push_back（FlashStream（url，headers，data，_npp.ndata，notifyData，lastModified））; 
 // ... 
  

有时我在在 FlashStream （当我 push_back（） c $ c>到向量< FlashStream> _streams 。

我阅读了这个问题在SO 和另外几个，但是所有相同的不知道如何优雅和有效地解决问题。可能是问题是在复制构造函数，但我不知道如何可以使用内存分配 NPStream.headers 和 NPStream.url

解决方案

p $ p> _streams.push_back（FlashStream（url，headers，data，_npp.ndata，notifyData，lastModified））;


等效于：

  {
 FlashStream temp（url，headers，data，_npp.ndata，notifyData，lastModified）; 
 _streams.push_back（temp）; 
 // temp get destroyed here 
} 
  

FlashStream对象被复制到向量中，然后被破坏。您可以使用C ++ 11中的 emplace_back（）避免这种情况：

  _streams.emplace_back（url，headers，data，_npp.ndata，notifyData，lastModified）; 
  

I have this class definition:

class FlashStream
{
public:
    explicit FlashStream(const char * url, vector<uint8> * headers, vector<uint8> * data, void * ndata, void * notifyData = NULL, uint32 lastModified = NULL);
    ~FlashStream();
private:        
    NPStream      _stream;
    // ...
}

(NPStream description)

and its implemetation:

FlashStream::FlashStream(const char * url, vector<uint8> * headers, vector<uint8> * data, void * ndata, void * notifyData, uint32 lastModified)
{
    // ...
    memset(&_stream, 0, sizeof(NPStream));

    _stream.headers = new char[data->size()]; 

    memcpy((void*)_stream.headers, &(*data)[0], data->size());
    // ...
}

FlashStream::~FlashStream()
{
    // ...
    if(_stream.headers)
        delete [] _stream.headers;
    _stream.headers = NULL;
    // ...
}

Now, when I run this code:

// ...
vector<FlashStream> _streams;
// ...
_streams.push_back(FlashStream(url, headers, data, _npp.ndata, notifyData, lastModified));
// ...

Sometimes I have an error at delete [] _stream.headers; in the destructor of FlashStream, which is called when I push_back() to the vector<FlashStream> _streams.

I read this question on SO and a few another, but all the same don't know how to elegantly and efficiently fix the problem. May be the problem is in copy constructor, but I don't know how I can make it with memory allocation for NPStream.headers and NPStream.url?

解决方案

This statement:

_streams.push_back(FlashStream(url, headers, data, _npp.ndata, notifyData, lastModified));

is equivalent to:

{
    FlashStream temp(url, headers, data, _npp.ndata, notifyData, lastModified);
    _streams.push_back(temp);
    // temp gets destroyed here
}

so, you create a temporary FlashStream object that is copied into the vector, then destructed afterwards. You can avoid this by using emplace_back() in C++11:

_streams.emplace_back(url, headers, data, _npp.ndata, notifyData, lastModified);

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