错误：非静态引用成员，无法使用默认赋值运算符

Error: non-static reference member, can't use default assignment operator

本文关键字：默认 赋值运算符 静态 引用 成员 错误      更新时间：2023-10-16

我正在调整一个现有的库（"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。每个图书馆单独运作都很好。Webduino库希望使用SPI上的以太网硬件模块，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

以下是相关的代码片段。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();，如果我指出问题消失了（但整个事情都依赖于这一行）。实际的问题似乎是，当WiFiClient对象被分配时，_WiFly成员无法初始化（覆盖？），但我不明白为什么它在没有修改的情况下工作时不能在这里工作。

（是的，我知道头文件中有实现，我不知道他们为什么这么写，别怪我！）

有什么见解吗？

WiFlyClient的WiFly成员使类不可赋值。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

由于所有的WiFlyClient都引用相同的WiFlyDevice实例，因此可以按照编译器建议使用静态成员的方式更改WiFlyClient：

// 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初始化它

WiFlyDevice & WiFlyClient::_WiFly = WiFly;

显然问题在于WiFlyClient是不可赋值的。考虑将它包含在std::unique_ptr中（在C++03中，std::auto_ptr），这样您至少可以分配该类型的项。

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>

尝试覆盖operator=:

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