错误：非静态引用成员，不能使用默认赋值运算符

Question

我正在调整现有的库（“Webduino”，Arduino的Web服务器）与另一个现有的库（“WiFly”，一个wifi模块）一起工作并遇到问题。 每个图书馆都可以自行运作。 Webduino库期望通过SPI使用以太网硬件模块，而WiFi模块使用串行端口（UART）。 我得到的错误是：

WiFlyClient.h: In member function 'WiFlyClient& WiFlyClient::operator=(const WiFlyClient&)':
WiFlyClient.h:14:
error: non-static reference member 'WiFlyDevice& WiFlyClient::_WiFly', can't use default assignment operator
WiFlyWebServer.h: In member function 'void WebServer::processConnection(char*, int*)':
WiFlyWebServer.h:492: note: synthesized method 'WiFlyClient& WiFlyClient::operator=(const WiFlyClient&)' first required here

以下是相关的代码段。 请注意，到目前为止，我只修改了WiFlyWebServer.h（Webduino）：

// WiFlyWebServer.h (Webduino)
...
WiFlyServer m_server; // formerly EthernetServer and
WiFlyClient m_client; // EthernetClient
...
void WebServer::processConnection(char *buff, int *bufflen){
  ...
  // line 492
  m_client = m_server.available();
  ...
}



// WiFlyClient.h
class WiFlyClient : public Client {
 public:
  WiFlyClient();
  ...
private:
  WiFlyDevice& _WiFly;
  ...
}



// WiFlyClient.cpp
#include "WiFly.h"
#include "WiFlyClient.h"

WiFlyClient::WiFlyClient() :
  _WiFly (WiFly) {    // sets _wiFly to WiFly, which is an extern for WiFlyDevice (WiFly.h)
  ...
}


// WiFly.h
#include "WiFlyDevice.h"
...
extern WiFlyDevice WiFly;
...



// WiFlyDevice.h
class WiFlyDevice {
  public:
    WiFlyDevice(SpiUartDevice& theUart);
...



// WiFlyDevice.cpp
WiFlyDevice::WiFlyDevice(SpiUartDevice& theUart) : SPIuart (theUart) {
  /*

    Note: Supplied UART should/need not have been initialised first.

   */
  ...
}

问题源于m_client = m_server.available(); 如果我评论说问题消失了（但整个事情依赖于那条线）。 实际问题似乎是在分配WiFiClient对象时，_WiFly成员无法初始化（覆盖？），但我无法理解为什么它在没有修改的情况下工作时不起作用。

（是的，我知道头文件中有实现，我不知道为什么他们这样写，不要怪我！）

任何见解？

Answer 1

该WiFly的成员WiFlyClient正在使类不可转让。 原因是赋值不能用于更改引用引用的对象。 例如：

int a = 1;
int b = 2;
int &ar = a;
int &br = b;
ar = br; // changes a's value to 2, does not change ar to reference b

由于所有WiFlyClient都引用相同的WiFlyDevice实例，因此您可以更改WiFlyClient因为编译器建议使用静态成员：

// WiFlyClient.h
class WiFlyClient : public Client {
 public:
  WiFlyClient();
  ...
private:
  static WiFlyDevice& _WiFly;
  ...
};

然后，您不在构造函数中初始化它，而是在您定义它的源文件中。

WiFlyDevice & WiFlyClient::_WiFly = WiFly;

Answer 2

显然问题是WiFlyClient不可分配。 考虑在std::unique_ptr （在C ++ 03， std::auto_ptr ）中包含它，以便至少可以分配该类型的项目。

std::unique_ptr<WiFlyClient> m_client;

...

m_client = m_server.available();

...

// convert m_client.<...> to m_client-><...>

// change m_server.available() to return std::unique_ptr<WiFlyClient>

Answer 3

尝试重写operator= ：

WiFlyClient& operator= (const WiFlyClient & wi)
{
  /* make a copy here */ 
  return *this;
}