Random-Access Write a binary file - C++ File Stream

C++ examples for File Stream:Binary File

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Description

Random-Access Write a binary file

Demo Code

#include <iostream>
#include <fstream>
using namespace std;
int get_int(int default_value);
int main() {/*  w  w w. j ava  2s .  com*/
   char filename[FILENAME_MAX];
   int n = 0;
   char name[20];
   int age = 0;
   int recsize = sizeof(name) + sizeof(int);
   cout << "Enter file name: ";
   cin.getline(filename, FILENAME_MAX);
   // Open file for binary write.
   fstream  fbin(filename, ios::binary | ios::out);
   if (!fbin) {
      cout << "Could not open " << filename << endl;
      return -1;
   }
   //  Get record number to write to.
   cout << "Enter file record number: ";
   n = get_int(0);
   // Get data from end user.
   cout << "Enter name: ";
   cin.getline(name, sizeof(name) - 1);
   cout << "Enter age: ";
   age = get_int(0);
   // Write data to the file.
   fbin.seekp(n * recsize);
   fbin.write(name, sizeof(name) - 1);
   fbin.write((char*)(&age), sizeof(int));
   fbin.close();
   return 0;
}
#define COL_WIDTH 80  // 80 is typical column width
int get_int(int default_value) {
   char s[COL_WIDTH+1];
   cin.getline(s, COL_WIDTH);
   if (strlen(s) == 0) {
      return default_value;
   }
   return atoi(s);
}

Result


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