C ++中的编译器错误

Question

Here is the error I am getting.

CruiseShip.h:10: error: expected ';' before '::' token

CruiseShip.cpp:8: error: expected ')' before 'name' make: ***

[CruiseShip.o] Error 1

CruiseShip.h

CruiseShip(std::string name,std::string year, int maxPassengers)::Ship(std::string name,std::string year);

CruiseShip.cpp

CruiseShip(string name, string year, int maxPassengers)::Ship(string name, string year){
    maxPassengers=0;
}

These are the line's where the error occurs.

Here is the rest of the code: CruiseShip.cpp

#include <iostream>
#include "Ship.h"
#include "CruiseShip.h"
using namespace std;



CruiseShip(string name, string year, int maxPassengers)::Ship(string name, string year){
    maxPassengers=0;
}

void CruiseShip::setPass(int maxPassengers){
    this->maxPassengers=maxPassengers;
}
int CruiseShip::getPass(){
    return maxPassengers;
}

void CruiseShip::print(){
    cout<<"The name of the ship is "<<getName()<<endl;
    cout<<"The capacity of the ship is "<<maxPassengers<<endl;

}

CruiseShip.h

#ifndef CRUISESHIP_H_
#define CRUISESHIP_H_
#include <string>
class CruiseShip: public Ship{
protected:
    int maxPassengers;


public:
    CruiseShip(std::string name,std::string year, int maxPassengers)::Ship(std::string name,std::string year);
    void setPass(int);
    int getPass();
    virtual void print();

};
#endif

Answer 1

Apparently, CruiseShip inherits from Ship .

The declaration should say only what the constructor's prototype is,

CruiseShip(std::string name, std::string year, int maxPassengers);

and the definition does the initialisation:

CruiseShip::CruiseShip(string name, string year, int maxPassengers) 
   : Ship(name, year),
     maxPassengers(maxPassengers) 
{

}

Note that there's only a single colon and that the base class initialization doesn't mention the types, just like a function call.
Also, the constructor definition needs the scope specification CruiseShip:: .

Answer 2

This line doesn't seem to make any sense.
What do you think it is supposed to do?

CruiseShip(std::string name,std::string year, int maxPassengers)::Ship(std::string name,std::string year);

It looks like the start of a constructor for class CruiseShip , but then has a scoping ( :: ) before starting to look like the constructor for class Ship .

Here is what I think you mean:

In Header(.h) file:

#pragma once
#include <string>
using std::string;
class CruiseShip :
    public Ship   // Class inherits from base-class Ship
{
    // Constructor takes 3 parameters:
    CruiseShip(const string& name, const string& year, int maxPassengers);
};

In Implementation(.cpp) File:

// Implementation of the Constructor, which begins by passing
// name and year to the Base-Class constructor.
// Then completes the constructor by handling the maxPassengers parameter.
CruiseShip::CruiseShip(const string& name, const string& year, int maxPassengers): 
    Ship(name, year)  // Call the base-class constructor
{
    this->maxPassengers = maxPassengers; // Also assign member variable.
}

---

A few other notes:

• You should generally pass variables by const-reference if you don't have a good reason for passing by value. This will avoid needless copy-constructors.

• Avoid the whole #ifdef - #endif protection by using #pragma once , which is supported by most major compilers now.

• Don't do using namespace std; . It brings in the entire namespace, which is really big. Just import what you need: using std::string; (see This Topic )

Answer 3

Your Ship class has to have something like this :

Ship(std::string,std::string);

in public declarations. Because this is what you are calling when you give parameters in CruiseShip

The way you make a correct constructor with inherence is this way :

CruiseShip::CruiseShip(string name, string year, int maxPassengers):Ship(name,year){
    maxPassengers=0;
}

You are calling the constructor with parameters Ship(std::string,std::string) that takes parameters given by CruiseShip . And you simply tell the program which variables you are giving

Your CruiseShip class because it's wrong. You don't tell the program to call Ship first

#ifndef CRUISESHIP_H_
#define CRUISESHIP_H_
#include <string>
class CruiseShip: public Ship{
protected:
    int maxPassengers;


public:
    CruiseShip(std::string name,std::string year, int maxPassengers);
    void setPass(int);
    int getPass();
    virtual void print();

};
#endif