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Ch8函数探幽/引用变量/对象继承和引用/filefunc.cpp

+//filefunc.cpp -- function with ostream & parameter
+#include <iostream>
+#include <fstream>
+#include <cstdlib>
+using namespace std;
+
+void file_it(ostream& os, double fo, const double fe[], int n);
+const int LIMIT = 5;
+
+int main(void)
+{
+	ofstream fout;
+	const char* fn = "ep-data.txt";
+	fout.open(fn);
+	if (!fout.is_open())
+	{
+		cout << "Can't open " << fn << ". Bye.\n";
+		exit(EXIT_FAILURE);
+	}
+	double objective;
+	cout << "Enter the focal length of your "
+		"telescope objective in mm: ";
+
+	cin >> objective;
+	double eps[LIMIT];
+	cout << "Enter the focal length, in mm, of " << LIMIT
+		<< " eyepieces:\n";
+	for (int i = 0; i < LIMIT; i++)
+	{
+		cout << "Eyepiece # " << i + 1 << " : ";
+		cin >> eps[i];
+	}
+
+	file_it(fout, objective, eps, LIMIT);
+	file_it(cout, objective, eps, LIMIT);
+	cout << "Done\n";
+	return 0;
+}
+
+void file_it(ostream& os, double fo, const double fe[], int n)
+{
+	ios_base::fmtflags initial;
+	initial = os.setf(ios_base::fixed);		//save initial formatting state
+	os.precision(0);
+	os << "Focal length of objective: " << fo << " mm\n";
+	os.setf(ios::showpoint);
+	os.precision(1);
+	os.width(12);
+	os << "f.1. eyepiece";
+	os.width(15);
+
+	os << "magnification" << endl;
+	for (int i = 0; i < n; i++)
+	{
+		os.width(12);
+		os << fe[i];
+		os.width(15);
+		os << int(fo / fe[i] + 0.5) << endl;
+	}
+	os.setf(initial);		//restore initial formatting state
+}