fileio3.cpp

Code

/*
    fileio3.cpp
    David Klick
    CIS 250
    2017-10-06

    demonstration of random access file I/O
*/
#include <fstream>
#include <iostream>
using std::cout;
using std::endl;
using std::ifstream;
using std::ofstream;
using std::ios;

// this struct defines what the record is in the file
struct recType {
    int n;
    float x;
};

int main(void) {
    int i;
    recType rec;
    rec.x = 0.0f;

    // open output file as binary
    ofstream ofile("testfileio3.bin", ios::binary);
    if (!ofile) {
        cout << "Error: couldn't open output file" << endl;
        return 1;
    }

    // whole record is written at once to disk
    for (i=1; i<10; i++) {
        rec.n = i;
        ofile.write(reinterpret_cast<char *>(&rec), sizeof(rec));
        rec.x += 25;
    }
    ofile.close();

    // open file for input as binary
    ifstream ifile("testfileio3.bin", ios::binary);
    if (!ifile) {
        cout << "Error: couldn't open input file" << endl;
        return 2;
    }

    // find out how many records are in the file
    ifile.seekg(0L, ios::end);
    long numrecs = ifile.tellg() / sizeof(rec);

    // don't forget to get back to start of file
    ifile.seekg(0L, ios::beg);

    // read data in record-size chunks
    for (i=0; i<numrecs; i++) {
        ifile.read(reinterpret_cast<char *>(&rec), sizeof(rec));
        cout << rec.n << ", " << rec.x << endl;
    }
    ifile.close();

    return 0;
}