编译Stroustrup的图形库时出错

Question

我正在尝试使用C ++运行Stroustrup的原理和实践中的示例程序，该程序使用Bjarne的library，例如Simple_window.h，Graph.h，Point.h。它引发了一系列错误。 This SO question帮助修复了函数Window的歧义，但仍然存在很多错误。

#include "Simple_window.h"
#include "Graph.h"
int main()
{
    using namespace Graph_lib;   // our graphics facilities are in Graph_lib

Point tl(100,100);           // to become top left  corner of window

Simple_window win(tl,600,400,"Canvas");    // make a simple window

Polygon poly;                // make a shape (a polygon)

poly.add(Point(300,200));    // add a point
poly.add(Point(350,100));    // add another point
poly.add(Point(400,200));    // add a third point 

poly.set_color(Color::red);  // adjust properties of poly

win.attach (poly);           // connect poly to the window

win.wait_for_button();       // give control to the display engine
}

然后抛出以下错误

    In file included from GUI.h:11:0,
                 from Simple_window.h:2,
                 from first.cpp:7:
Graph.h:159:25: warning: narrowing conversion of ‘fl_color()’ from ‘Fl_Color {aka unsigned int}’ to ‘int’ inside { } [-Wnarrowing]
  Color lcolor {fl_color()};

我用g ++编译它，操作系统是Linux Mint。