warning: taking address of temporary

/*
    Triangle.cpp
*/

// Use a pure virtual function.

#include <iostream>
#include <cstring>
using namespace std;

// A class for two-dimensional objects.
class TwoDShape {
    // these are private
    double width;
    double height;

    // add a name field
    char name[20];
public:

    // Default constructor.
    TwoDShape() {
        width = height = 0.0;
        strcpy(name, "unknown");
    }

    // Constructor for TwoDShape.
    TwoDShape(double w, double h, char *n) {
        width = w;
        height = h;
        strcpy(name, n);
    }

    // Construct object with equal width and height.
    TwoDShape(double x, char *n) {
        width = height = x;
        strcpy(name, n);
    }

    void showDim() {
        cout << "Width and height are " << width << " and " << height <<
"\n";
    }

    // accessor functions
    double getWidth() { return width; }
    double getHeight() { return height; }
    void setWidth(double w) { width = w; }
    void setHeight(double h) { height = h; }
    char *getName() { return name; }

    // area() is now a pure virtual function
    virtual double area() = 0;

};

// Triangle is derived from TwoDShape.
class Triangle : public TwoDShape {
    char style[20]; //now private
public:

    /* A default constructor. This automatically invokes
        the default constructor of TwoDShape. */
    Triangle() {
        strcpy(style, "unknown");
    }

    // Constructor with three parameters.
    Triangle(char *str, double w, double h)
                : TwoDShape(w, h, "triangle") {
        strcpy(style, str);
    }

    // Construct an isosceles triangle.
    Triangle(double x) : TwoDShape(x, x, "triangle") {
        strcpy(style, "isosceles");
    }

    // This now overrides area() declared in TwoDShape.
    double area() {
        return getWidth() * getHeight() / 2;
    }

    void showStyle() {
        cout << "Triangle is " << style << "\n";
    }
};

int main() {
    // declare an array of pointers to TwoDShape objects.
    TwoDShape *shapes[4];

    shapes[0] = &Triangle("right", 8.0, 12.0);
    shapes[1] = &Triangle(3.0);
    shapes[2] = &Triangle(4.0);
    shapes[3] = &Triangle(7.0);

    for(int i=0; i < 2; i++) {
        cout << "object is " <<
                shapes[i]->getName() << "\n";

        cout << "Area is " <<
                shapes[i]->area() << "\n";

        cout << "\n";
    }

    return 0;
}

Hi, I'm a beginning programmer. Above is the code that is giving me
the error. I have talked with a professor about this issue. The
error happens on the lines beginning "shapes[0] = ... "

The professor says, because Triangle was created without a variable
they are temporary objects. Which means they will be destroyed and
the pointer becomes a dangling pointer.

I edited the code and just created the objects and gave them a
variable to be stored in. i.e. "Triangle t1("right", 4, 5);" Then I
just do "shapes[0] = &t1;" When I recompile, I get no warnings and it
runs as expected.

My question: Is there a way so that the temporary objects are not
destroyed? Seems like a waste of memory to create a variable outside
of the array that will always be referenced through the array.