Question

我从一本书中自学了C ++。我陷入了四步中的第二步。这第二部分，虽然我告诉我必须＆＃34;使这个类通用，以便形状的边可以是整数或浮动。＆＃34;

到目前为止，它是一个非常简单的程序。它有三个脚本。有main.cpp，shape.cpp和shape.h。

程序采用字符串中的对象名称，长度为浮点数，重要的是侧面。我有一个构造函数，它将对象，边和长度放在一起以创建一个通用的形状对象，我将在稍后进行升级。

但现在是让它更通用，所以我认为这与模板命令有关。它可能非常简单，我很抱歉浪费你的时间。似乎我必须改变线形状形状（object，objectSides，objectLength）;但我不确定以哪种方式，因为其他示例似乎表明你在标题和其他类中这样做。

的main.cpp

#include <iostream>
#include "shape.h"

using namespace std;

int main() {
//Setting variables to 0;
    string object;
    int objectSides = 0;
    int objectSidesTemp = 0;
    float objectLength = 0;
    float objectLengthTemp = 0;

//Taking input for user on object being made.
    cout << "Object to make: ";
    cin >> object;

//Input for sides being inputted. If below 3, asks user again for a valid number.
//Assigns in temp number until within bounds, then assigns to objectSides.
    while (objectSidesTemp < 3){
    cout << "How many sides (Must be 3 or greater): ";
    cin >> objectSidesTemp;
    }
    objectSides = objectSidesTemp;

//Input for length being inputted. If 0 or below, asks user again for a valid number.
//Assigns in temp number until within bounds, then assigns to objectLength.
    while (objectLengthTemp <= 0){
    cout << "Length of sides: ";
    cin >> objectLengthTemp;
    }
    objectLength = objectLengthTemp;

//Creates object of Shape called shape. Inputs the object name, sides, and length.
    Shape shape(object, objectSides, objectLength);

//Displays object specifics.
    shape.display();
}

shape.h

#ifndef SHAPE_H
#define SHAPE_H

#include <string>

using namespace std;

template <class T>
class Shape {

public:
    Shape(string, T, float);
    void setObject(string); //Used to ensure constructor works
//    virtual void setObject(string) = 0;
//Used setObject as virtual function since constructor uses it to
//Make the object using the setObject function.
    string getObject();
    T getSides();
    bool setSides(T);
    float getLength();
    void setLength (float);

    float getPerimeter(int, float);
    float getArea (int, float);

    void display();
private:
    string object;
    T sides;
    float length;
};

#endif

shape.cpp

#include <iostream>
#include <string>
#include "shape.h"

using namespace std;

//Constructor of Shape. Inpunts shape, sides, and length.
    Shape::Shape (string shapes, int sides, float length){
        setObject(shapes);
        setSides(sides);
        setLength(length);
    } //End of Shape constructor

//Method to request the amount of sides, returns as an int
//Because there are no lesser than full sides.
    template <class T>
    T Shape::getSides() {
        return sides;
    } //End of function getSides

//Method to set the amount of sides. Return method is a bool.
//If sideNumber is 0 or less in sides, returns a false.
//If sideNumber is greater than 1, returns true.
//Would recommend setting minimum of sides to 3 or greater,
//as anything less is either a shape, a dot, or nothing.
    bool Shape::setSides(int sideNumber) {
        if (sides > 0){
            sides = sideNumber;
            return true;
        }
        else {
            return false;
        }
    } //End of function setSides

//Returns string tied to the shape's object.
//Future in 2D suggests triangle, rectangle, or square.
//Implimented currently as any string.
    string Shape::getObject(){
        return object;
    } //End of function getObject

//Sets input of the string to the variable object.
    void Shape::setObject(string obj){
        object = obj;
    } //End of function setObject

//Retrieves float of length, as length can be numbers with decimals.
    float Shape::getLength(){
        return length;
    } //End of function getLength

//Sets length of the object. Uses void because it doesn't need to return anything.
    void Shape::setLength(float objectLength){
        length = objectLength;
    } //End of function setLength

//Sets area usings 3 sides or 4 sides else returns a 0.
//Returning as float because objectLength is used as a float.
    float Shape::getArea (int objectSides, float objectLength) {
        if (objectSides == 3){
            return (objectSides * objectLength) / 2;
        }
        if (objectSides == 4){
            return (objectLength * objectLength);
        }
//        return objectSides * objectLength;
        return 0;
    } //End of function getArea

//Float return of that parimeter. Multipling sides by length to achieve.
    float Shape::getPerimeter (int objectSides, float objectLength){
        return objectSides * objectLength;
    } //End of function getParimeter.

//Display function shows the Shape's varaibles.
//Uses getParimeter and getArea commands to generate further information of the shape.
    void Shape::display() {
        cout << "Object: " << object << endl;
        cout << "Sides: " << sides << endl;
        cout << "Length: " << length << endl;
        cout << "Perimeter: " << getPerimeter(sides, length) << endl;
        cout << "Area: " << getArea(sides, length) << endl;
    } //End of function display.

Answer 1

您将Shape定义为类模板，只使用一个模板参数 T：

template <class T>
class Shape { /* ... */ };

因此，您需要在实例化T时明确指定Shape：

Shape<int> shape(object, objectSides, objectLength);
//    ^^^

C ++缺少模板参数问题

1 个答案: