BYR Achieve · 镜像论坛

[求助]帮忙看下这是为什么

2008/7/6镜像同步7 回复

#include <iostream> #include <fstream> #include <iomanip> #include <cstdlib> inline void eatline(){while (std::cin.get() != '\n') continue;} const int LIM = 20; struct planet { char name[LIM]; double population; double g; }; const char * file = "planet.dat"; int main() { using namespace std; planet pl; cout << fixed << right; /* ifstream fin; fin.open(file, ios_base::in | ios_base::binary); if (fin.is_open()) { cout << "Here are the current contents of the " << file << " file: \n"; while (fin.read((char*)&pl, sizeof pl)) { cout << setw(LIM) << pl.name << ":" << setprecision(0) << setw(12) << pl.population << setprecision(2) << setw(6) << pl.g << endl; } fin.close(); } ofstream fout(file, ios_base::out | ios_base::binary | ios_base::app); if (!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, LIM); while (pl.name[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"; cin.get(pl.name, LIM); } fout.close(); fin.clear(); fin.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(LIM) << pl.name << ":" << setprecision(0) << setw(12) << pl.population << setprecision(2) << setw(6) << pl.g << endl; } fin.close(); } else { cerr << "Error on opening\n"; exit(EXIT_FAILURE); } */ /**********************************************************************************/ fstream finout; finout.open(file, ios_base::in | ios_base::out | ios_base::binary); int ct = 0; if (finout.is_open()) { finout.seekg(0); // go to beginning cout << "Here are the current contents of the" << file << " file: \n"; while (finout.read( (char*)&pl, sizeof pl) ) { cout << ct++ << ": " << setw(LIM) << pl.name << ": " << setprecision(0) << setw(12) << pl.population << setprecision(2) << setw(6) << pl.g << endl; } if (finout.eof()) finout.clear(); else { cerr << "Error in reading " << file << ".\n"; exit(EXIT_FAILURE); } } else { cerr << file << " could not be opened -- bye.\n"; exit(EXIT_FAILURE); } cout << "Enter the record number you wish to change:"; int num; cin >> num; //加上前面被注释掉的代码这里为什么就输入不了了? eatline(); if (num < 0 || num >= ct) { cerr << "Invalid record number -- bye.\n"; exit(EXIT_FAILURE); } streampos place = num * sizeof pl; finout.seekg(place); if (finout.fail()) { cerr << "Error on attempted seek.\n"; exit(EXIT_FAILURE); } finout.read( (char*)&pl, sizeof pl ); cout << "Your selection:\n"; cout << num << ": " << setw(LIM) << pl.name << ": " << setprecision(0) << setw(12) << pl.population << setprecision(2) << setw(6) << pl.g << endl; if (finout.eof()) finout.clear(); cout << "Enter planet name:"; cin.get(pl.name, LIM); eatline(); cout << "Enter planetary population:"; cin >> pl.population; cout << "enter planet's acceleration of gravity:"; cin >> pl.g; finout.seekp(place); finout.write( (char*)&pl, sizeof pl ) << flush; if (finout.fail()) { cerr << "Error on attempted write\n"; exit(EXIT_FAILURE); } ct = 0; finout.seekg(0); cout << "Here are the current contents of the" << file << " file: \n"; while (finout.read( (char*)&pl, sizeof pl) ) { cout << ct++ << ": " << setw(LIM) << pl.name << ": " << setprecision(0) << setw(12) << pl.population << setprecision(2) << setw(6) << pl.g << endl; } if (finout.eof()) finout.clear(); else { cerr << "Error in reading " << file << ".\n"; exit(EXIT_FAILURE); } finout.close(); cout << "Bye.\n"; return 0; }

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