尝试将元素推入向量 [英] Trying to push an element in to a vector

问题描述

在一个头文件（我没有写），一个结构已经定义如下

  struct MemoryMessage： public boost :: counted_base {/ *，public FastAlloc * / 
显式MemoryMessage（MemoryMessageType aType）
：theType（aType）{} 
显式MemoryMessage（MemoryMessageType aType，MemoryAddress anAddress）
：aType（aType）{} 
显式MemoryMessage（MemoryMessageType aType，MemoryAddress anAddress，int anIdentifier）
：theType（aType）{} 
 explicit MemoryMessage（MemoryMessageType aType，MemoryAddress anAddress，VirtualMemoryAddress aPC ）
：aType（aType）{} 
显式MemoryMessage（MemoryMessageType aType，MemoryAddress anAddress，VirtualMemoryAddress aPC，DataWord aData）
： & aMsg）
：theType（aMsg.theType）{} 
} 
  

稍后在我的代码中，我写了

  MemoryMessage testMsg; 
 class foo（）{
 foo（）
：testMsg（MemoryMessage :: test）
 {} 
 std :: vector< MemoryMessage>候选人; 
 
 void bar（）{
 candidates.push_back（testMsg）; 
} 
} 
  

但我收到此错误

 错误：没有匹配的函数调用'MemoryMessage :: MemoryMessage（const MemoryMessage&）'
注意：候选者是：MemoryMessage :: MemoryMessage （MemoryMessage&）
  

这有什么问题？我创建了一个非常小的代码段。

解决方案

此行背后的行调用一个复制构造函数：

  candidates.push_back（testMsg）; 
  

testMsg > std :: vector 中的复制构造函数将 const 引用放入向量中c $ c>的代码。但是，你的构造函数声明为 explicit ，所以 std :: vector 的代码不能访问它。



从复制构造函数中删除显式指示符将解决此问题。

In a header file (which I haven't written), a struct has been defined like this

struct MemoryMessage : public boost::counted_base { /*, public FastAlloc*/
  explicit MemoryMessage(MemoryMessageType aType)
   : theType(aType) {}
  explicit MemoryMessage(MemoryMessageType aType, MemoryAddress anAddress)
   : theType(aType) {}
  explicit MemoryMessage(MemoryMessageType aType, MemoryAddress anAddress, int anIdentifier)
   : theType(aType) {}
  explicit MemoryMessage(MemoryMessageType aType, MemoryAddress anAddress, VirtualMemoryAddress aPC)
   : theType(aType) {}
  explicit MemoryMessage(MemoryMessageType aType, MemoryAddress anAddress, VirtualMemoryAddress aPC, DataWord aData)
   : theType(aType) {}
  explicit MemoryMessage(MemoryMessage & aMsg)
   : theType(aMsg.theType) {} 
}

Later in my code, I have written

MemoryMessage testMsg;
class foo() {
  foo()
   : testMsg(MemoryMessage::test)
  {}
  std::vector< MemoryMessage > candidates;

  void bar() {
     candidates.push_back(testMsg);   
  }
}

But I get this error

error: no matching function for call to 'MemoryMessage::MemoryMessage(const MemoryMessage&)’
note: candidates are:MemoryMessage::MemoryMessage(MemoryMessage&)

What is wrong with that? I created a very small snippet. Please let me know if I missed something in my explanation.

解决方案

This line behind the scene invokes a copy constructor:

candidates.push_back(testMsg);   

The testMsg that push_back takes by const reference is placed into the vector by invoking a copy constructor inside std::vector's code. However, your constructor is declared explicit, so std::vector's code cannot access it.

Removing explicit designator from the copy constructor will fix this problem.

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