(2011.07.26)以二进制方式读写文件（C++ Primer Plus)

// binary.cpp -- binary file I/O#include <iostream>// not required by most systems#include <fstream>#include <iomanip>#include <cstdlib>// (or stdlib.h)for exit()inline void eatline() { while(std::cin.get()!= '\n') continue; }struct planet{char name[20];// name of planetdouble population;// its populationdouble g;// its acceleration of gravity};const char * file = "planets.dat";int main(){using namespace std;planet pl;cout << fixed << right;// show initial contentsifstream fin;fin.open (file, ios_base::in | ios_base::binary);// binary file// NOTE: some systems don't accept the ios_base::binary modeif (fin.is_open()){cout << "Here are the current contents of the "<< file << " file: \n";while(fin.read((char *) &pl, sizeof pl)){cout << setw(20) << pl.name << ": "<< setprecision (0) << setw(12) << pl.population << setprecision (2) << setw(6) << pl.g << endl;}fin.close();}// add new data ofstream fout (file, ios_base::out | ios_base::app | ios_base::binary);//NOTE: some systems don't accept the ios::binary modeif(!fout.is_open()){cerr << "Can't open " << file << " file for output: \n";exit(EXIT_FAILURE);}cout << "Enter planet name(enter a blank line to quit): \n";cin.get(pl.name, 20);while(pl.name[0]!= '\0'){eatline();cout << "Enter planetary population: ";cin >> pl.population;cout << "enter planet's acceleration of gravity: ";cin >> pl.g;eatline();fout.write((char *)&pl, sizeof pl);cout << "Enter planet name (enter a blank line to quit):\n";}fout.close();// show revised filefin.clear();// not required for some implementations, but won't hurtfin.open (file, ios_base::in | ios_base::binary);if(fin.is_open()){cout << "Here are the new contents of the "<< file << " file: \n";while(fin.read((char*)&pl, sizeof pl)){cout << setw(20) << pl.name << ": "<< setprecision(0) << setw(12) << pl.population << setprecision(2) << setw (6) << pl.g << endl;}fin.close();}cout << "Done.\n";return 0;}