c++ - 错误 : non-static reference member, 无法使用默认赋值运算符

Question

我正在调整一个现有库(“Webduino”，Arduino 的 Web 服务器)以与另一个现有库(“WiFly”，一个 wifi 模块)一起工作，但遇到了问题。每个库都可以独立运行。 Webduino 库希望通过 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

这里是相关的代码片段。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();，如果我注释掉问题就消失了(但整个事情都依赖于那条线)。实际问题似乎是 _WiFly 成员在分配 WiFiClient 对象时无法初始化(覆盖？)，但我不明白为什么它在没有修改的情况下工作时在这里不起作用。

(是的，我知道头文件里有实现，我不知道他们为什么这么写，不要怪我!)

有什么见解吗？

Answer 1

WiFlyClient 的 WiFly 成员使该类不可分配。原因是赋值不能用于更改引用所指的对象。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

由于您所有的 WiFlyClient 都引用相同的 WiFlyDevice 实例，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，而是在定义它的源文件中进行初始化。

WiFlyDevice & WiFlyClient::_WiFly = WiFly;