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