我是 C++ 的新手,正在尝试理解这种语言中的继承。我已经创建了一个 Ship
类,定义了一些构造函数、修改器和一个 print
函数,该函数应该 cout
关于这艘船的一些信息。我有两个派生类,一个是 Cruise
类,另一个是 Cargo
类。我第一次编译 Cruise
类的测试时一切正常。实现 Cargo
类后,我无法再编译我的代码。这两个类非常相似并且实现几乎相同。这是我的代码,我收到的错误在下面。
ship.cpp(定义船级)
#include <iostream>
#include <string>
using namespace std;
class Ship {
private:
string _strName, _strYear;
public:
//Constructors
Ship();
Ship(string, string);
//Mutators
void setName(string);
void setYear(string);
string getName();
string getYear();
//Methods
virtual void print();
};
//*************************************
// Cunstructors *
//*************************************
Ship::Ship() {
_strName = "NONE";
_strYear = "NONE";
}
Ship::Ship(string strname, string strYear) {
setName(strname);
setYear(strYear);
}
//*************************************
// MUTATORS *
//*************************************
void Ship::setName(string strName) {
_strName = strName;
}
void Ship::setYear(string strYear) {
_strYear = strYear;
}
string Ship::getName() {
return _strName;
}
string Ship::getYear() {
return _strYear;
}
//*************************************
// METHODS *
//*************************************
virtual void Ship::print() {
cout << _strName << endl
<< _strYear << endl;
}
CuiseShip.cpp(继承Ship的游轮类)
#include <iostream>
#include <string>
#include "ship.cpp"
using namespace std;
class CruiseShip:public Ship {
private:
int _intMaxPassengers;
public:
//Constructors
CruiseShip();
CruiseShip(string, string, int);
//Mutators
void setMaxPassengers(int);
int getMaxPassengers();
//Methods
void print();
};
//*************************************
// Cunstructors *
//*************************************
CruiseShip::CruiseShip() {
setName("NONE");
setYear("NONE");
setMaxPassengers(0);
}
CruiseShip::CruiseShip(string strname, string strYear, int intMaxPassengers) {
setName(strname);
setYear(strYear);
setMaxPassengers(intMaxPassengers);
}
//*************************************
// MUTATORS *
//*************************************
void CruiseShip::setMaxPassengers(int intMaxPassengers) {
_intMaxPassengers = intMaxPassengers;
}
int CruiseShip::getMaxPassengers() {
return _intMaxPassengers;
}
//*************************************
// METHODS *
//*************************************
void CruiseShip::print() {
string name = getName();
string year = getYear();
string maxPassengers = to_string(getMaxPassengers());
cout << name << endl
<< year << endl
<< maxPassengers << endl;;
}
CargoShip.cpp(继承自ship)
#include <iostream>
#include <string>
#include "ship.cpp"
using namespace std;
class CargoShip: public Ship {
private:
int _intCapacity;
public:
//Constructors
CargoShip();
CargoShip(string, string, int);
//Mutators
void setCapacity(int);
int getCapacity();
//Methods
void print();
};
//*************************************
// Cunstructors *
//*************************************
CargoShip::CargoShip() {
setName("NONE");
setYear("NONE");
setCapacity(0);
}
CargoShip::CargoShip(string strname, string strYear, int intCapacity) {
setName(strname);
setYear(strYear);
setCapacity(intCapacity);
}
//*************************************
// MUTATORS *
//*************************************
void CargoShip::setCapacity(int intCapacity) {
_intCapacity = intCapacity;
}
int CargoShip::getCapacity() {
return _intCapacity;
}
//*************************************
// METHODS *
//*************************************
void CargoShip::print() {
string name = getName();
string year = getYear();
string capacity = to_string(getCapacity());
cout << name << endl
<< year << endl
<< capacity << endl;;
}
TEST.cpp(main() 用于实现和测试代码)
#include <iostream>
#include <string>
#include "CruiseShip.cpp"
#include "CargoShip.cpp"
int main() {
CruiseShip cruise("cruise", "1862", 25);
CargoShip cargo("Mellinium Falcon", "a long time ago", 100);
cruise.print();
cargo.print();
return 0;
}
编译错误
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:5:7: error: redefinition of ‘class Ship’
class Ship {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:5:7: error: previous definition of ‘class Ship’
class Ship {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:27:1: error: redefinition of ‘Ship::Ship()’
Ship::Ship() {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:27:1: note: ‘Ship::Ship()’ previously defined here
Ship::Ship() {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:31:1: error: redefinition of ‘Ship::Ship(std::__cxx11::string, std::__cxx11::string)’
Ship::Ship(string strname, string strYear) {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:31:1: note: ‘Ship::Ship(std::__cxx11::string, std::__cxx11::string)’ previously defined here
Ship::Ship(string strname, string strYear) {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:39:6: error: redefinition of ‘void Ship::setName(std::__cxx11::string)’
void Ship::setName(string strName) {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:39:6: note: ‘void Ship::setName(std::__cxx11::string)’ previously defined here
void Ship::setName(string strName) {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:43:6: error: redefinition of ‘void Ship::setYear(std::__cxx11::string)’
void Ship::setYear(string strYear) {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:43:6: note: ‘void Ship::setYear(std::__cxx11::string)’ previously defined here
void Ship::setYear(string strYear) {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:47:8: error: redefinition of ‘std::__cxx11::string Ship::getName()’
string Ship::getName() {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:47:8: note: ‘std::__cxx11::string Ship::getName()’ previously defined here
string Ship::getName() {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:51:8: error: redefinition of ‘std::__cxx11::string Ship::getYear()’
string Ship::getYear() {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:51:8: note: ‘std::__cxx11::string Ship::getYear()’ previously defined here
string Ship::getYear() {
^
In file included from CargoShip.cpp:3:0,
from Test.cpp:4:
ship.cpp:58:6: error: redefinition of ‘void Ship::print()’
void Ship::print() {
^
In file included from CruiseShip.cpp:3:0,
from Test.cpp:3:
ship.cpp:58:6: note: ‘void Ship::print()’ previously defined here
void Ship::print() {
^
这个错误对我影响不大,而且我似乎找不到解决方案。编译器似乎在告诉我,我正在尝试重新定义 Ship 类。谁能解释一下这是怎么回事?
最佳答案
您不应该从主文件中包含 .cpp 文件。想象#including .cpp 文件是复制和粘贴,并且您将 .cpp 文件包含在主文件和运送文件中 - 这会导致这些拷贝的多个拷贝,因此编译器会定义它不止一次。
您必须将类定义放在 .h 文件中 - WITH HEADER GUARDS 以防止重复,然后将实现细节放在 .cpp 文件中。示例:
船.hpp
// Protects from multiple copies
#ifndef _SHIP_H_
#define _SHIP_H_
#include <iostream>
#include <string>
using namespace std;
class Ship {
private:
string _strName, _strYear;
public:
//Constructors
Ship();
Ship(string, string);
//Mutators
void setName(string);
void setYear(string);
string getName();
string getYear();
//Methods
virtual void print();
};
#endif // _SHIP_H_
船.cpp
#include "ship.hpp" // this .cpp file INCLUDES the .hpp so it can match the functions
//*************************************
// Constructors *
//*************************************
Ship::Ship() {
_strName = "NONE";
_strYear = "NONE";
}
Ship::Ship(string strname, string strYear) {
setName(strname);
setYear(strYear);
}
//*************************************
// MUTATORS *
//*************************************
void Ship::setName(string strName) {
_strName = strName;
}
void Ship::setYear(string strYear) {
_strYear = strYear;
}
string Ship::getName() {
return _strName;
}
string Ship::getYear() {
return _strYear;
}
//*************************************
// METHODS *
//*************************************
virtual void Ship::print() {
cout << _strName << endl
<< _strYear << endl;
}
对其他文件重复相同的操作。
主要.cpp
#include <iostream>
#include <string>
#include "CruiseShip.hpp" // include .hpp files. Linker will link the .hpp functions with the .cpp implementations.
#include "CargoShip.hpp" // same here
int main() {
CruiseShip cruise("cruise", "1862", 25);
CargoShip cargo("Mellinium Falcon", "a long time ago", 100);
cruise.print();
cargo.print();
return 0;
}
要构建,您必须单独编译所有 .cpp 文件以确保它们没有名称冲突。它们将自动与 main.cpp 链接:
g++ --std=c++0x ship.cpp cargo.cpp main.cpp ...等等等等
关于c++ - 用子类覆盖基类中定义的函数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52940337/