"Declaration of xxx outside of class is not definition"错误

"Declaration of xxx outside of class is not definition" error

本文关键字：of not 错误 definition is outside Declaration xxx class      更新时间：2023-10-16

这是错误：

错误：类外"DataStream：：DataStream(("的声明不是定义[fPermission]|
||===生成完成：1个错误，0个警告(0分0秒(===|

这是主.cpp文件：

#include <iostream>
#include <iomanip>
#include "DataStream.h"
#include "MsgPacket.h"
using namespace std;
DataStream * Packet = new DataStream();
DataStream::DataStream();
int main()
{
    int source;
    int destination;
    int type;
    int port;
    int input;
    std::string data;
    cout << "My Assignment" << endl;;
    MsgPacket * Packet = new MsgPacket(source, destination, type, port, data);
}

这是MsgPacket.h

#ifndef MSGPACKET_H
#define MSGPACKET_H
#include <string>
#include "PacketAddress.h"
using namespace std;
class MsgPacket : public PacketAddress
{
public:
    MsgPacket();
    MsgPacket (const MsgPacket & rhs);
    MsgPacket(string dataIn);
    MsgPacket(int source, int destination, int port, int type, std::string data);
    MsgPacket(int, char data);
    string toString();
    string getData() const {return _data;};
    void setData(string inData) {_data = inData;};
    string dataOutput();
    virtual ~MsgPacket();
    virtual MsgPacket * Clone() { return new MsgPacket(*this); }
protected:
    string _data;
};
#endif // MSGPACKET_H

最后是MsgPacket.cpp

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <sstream>
#include <string>
#include <iomanip>
#include "msgpacket.h"
using namespace std;
MsgPacket::MsgPacket():
PacketAddress(0, 0)
{
}
MsgPacket::MsgPacket (const MsgPacket & rhs):
PacketAddress(rhs),
_data(rhs.getData())
{
}
MsgPacket::MsgPacket(string dataIn):
PacketAddress(0,0)
{
    string temp;
    temp = dataIn.substr (0, 4);
    _source = atoi(temp.c_str());
    temp = dataIn.substr (5, 4);
    _dest = atoi(temp.c_str());
    temp = dataIn.substr (10, 4);
    _type = atoi(temp.c_str());
    temp = dataIn.substr (15, 4);
    _port = atoi(temp.c_str());
    _data = dataIn.substr (20, dataIn.length());
    #ifdef DEBUG
    cout << "CREATE PACKET: " << this->toString() << endl;
    #endif
}
MsgPacket::MsgPacket(int source, int destination):
PacketAddress(source, destination)
{
}
MsgPacket::MsgPacket(int source, int destination, int port):
PacketAddress(source, destination)
{
    _port = port;
}
MsgPacket::MsgPacket(int source, int destination, int type, int port, std::string       data):
PacketAddress(source, destination)
{
    _source = source;
    _dest = destination;
    _type = type;
    _data = data;
    _port = port;
}
string MsgPacket::dataOutput()
{
    stringstream output; // Create a stringstream
    output << setw(4) << setfill('0') << _source << ":"
           << setw(4) << setfill('0') <<  _dest  << ":"
           << setw(4) << setfill('0') << _type   << ":"
           << setw(4) << setfill('0') << _port   << ":"
           << _data;
    return output.str();
}
string MsgPacket::toString()
{
    stringstream output; // Create a stringstream
    output << "[" << showbase << hex
           << this << "] S:["
           << _source << "] D:["
           << _dest << "] P:["
           << _type << "] T:["
           << _port << "]"
           << " DATA[" << _data << "]";
    return output.str();
}

另一种可能导致此错误的方法是下面的代码。

class A 
{
  void a_function();
};
A::a_function();   // Note the semicolon here
{
  // function contents...
}

如果你还没有摄入足够的咖啡因，那么额外的分号可能很难识别。。。

如果有人因为语法错误而来到这里，请注意，在初始化参数时，您可能会报告与语法错误相同的错误：

class A
{
  A ();
  char b;
};
A::A ()
, b(0)  // Wrong. It should be ':' instead of ','
{
}

DataStream::DataStream();

是类DataStream的构造函数的声明。它必须在类内声明，而不是在类外声明。

class DataStream
{
    public:
        DataStream();
};

此外，您可以在类内部或外部内联定义此构造函数，如

DataStream::DataStream()
{}

我设法得到这个错误的另一种方法是，通过定义对象的static std::vector，其类型是在类内部定义的：

template<typename Ty>
class MyTemplatedClass
{
public:
   struct AStructThatBelongsToMyTemplatedClass
   {
      uint32_t aU32ThatsPartOfTheStructThatBelongsToMyTemplatedClass;
   };
   static uint32_t u32;
   static AStructThatBelongsToMyTemplatedClass aStructInstance;
   static std::vector<uint32_t> vectOfu32;
   static std::vector<AStructThatBelongsToMyTemplatedClass> vectOfStructInstances;
};
template<typename Ty> uint32_t MyTemplatedClass<Ty>::u32;
template<typename Ty> std::vector<uint32_t> MyTemplatedClass<Ty>::vectOfu32;
// This produces error: need 'typename' before 'MyTemplatedClass<Ty>::AStructThatBelongsToMyTemplatedClass' because 'MyTemplatedClass<Ty>' is a dependent scope
//template<typename Ty> MyTemplatedClass<Ty>::AStructThatBelongsToMyTemplatedClass MyTemplatedClass<Ty>::aStructInstance;
// ...but this works ok:
template<typename Ty> typename MyTemplatedClass<Ty>::AStructThatBelongsToMyTemplatedClass MyTemplatedClass<Ty>::aStructInstance;
// This produces error: declaration of 'std::vector<MyTemplatedClass<Ty>::AStructThatBelongsToMyTemplatedClass> MyTemplatedClass<Ty>::vectOfStructInstances' outside of class is not definition
//template<typename Ty> std::vector<MyTemplatedClass<Ty>::AStructThatBelongsToMyTemplatedClass> MyTemplatedClass<Ty>::vectOfStructInstances;
// ...but this works ok (the only thing I added was 'typename'):
template<typename Ty> std::vector<typename MyTemplatedClass<Ty>::AStructThatBelongsToMyTemplatedClass> MyTemplatedClass<Ty>::vectOfStructInstances;

正如其他人已经提到的，这个错误很可能是因为语法错误。我有一个Declaration of SomeClass outside of class is not definition错误。问题是for循环后缺少}：

void A::a_function() {
  for (int i = 0; i < 20; ++i) {
    // loop code
  // note the missing } here
  // function code
}
SomeClass* A::getSomeClassInstance() {
  // function code
}
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