C++ File Streams, Binary I/O & Random Access File Pointers

Explanation

C++ stream architecture treats files as sequences of continuous bytes. Binary file I/O bypasses character conversion overhead, persisting in-memory objects directly to storage. Random access operations move the file read/write cursor via seekg/seekp with offsets ios::beg, ios::cur, or ios::end, enabling direct record indexing.

Key points

• File Open Modes: ios::in (read), ios::out (write/overwrite), ios::app (append), ios::binary (binary I/O), ios::ate (seek to end on open).
• Binary File I/O: read((char*)&obj, sizeof(obj)) and write((char*)&obj, sizeof(obj)) read/write raw memory byte buffers.
• File Pointers: get pointer (seekg to seek, tellg to get position); put pointer (seekp to seek, tellp to get position).
• Stream Status Flags: eof() (end of file), fail() (format error), bad() (hardware error), good() (healthy).

Example

Code examples

// Writing and Reading Class Objects to Binary Files in C++
#include <iostream>
#include <fstream>
using namespace std;

class StudentRecord {
public:
    int id;
    char name[30];
    float gpa;

    void input(int i, const char* n, float g) {
        id = i;
        strncpy(name, n, 29);
        name[29] = '\0';
        gpa = g;
    }
};

void saveRecord(const StudentRecord& s) {
    ofstream outFile("students.dat", ios::binary | ios::app);
    outFile.write(reinterpret_cast<const char*>(&s), sizeof(s));
    outFile.close();
}

void readAllRecords() {
    ifstream inFile("students.dat", ios::binary);
    StudentRecord s;
    while (inFile.read(reinterpret_cast<char*>(&s), sizeof(s))) {
        cout << "ID: " << s.id << ", Name: " << s.name << ", GPA: " << s.gpa << endl;
    }
    inFile.close();
}

Exam questions

• [8 Marks] Write a complete C++ program to store student records (roll, name, marks) in a binary file and search for a record by roll number using read() and seekg().
• [7 Marks] Explain file opening modes and the functions of seekg(), seekp(), tellg(), and tellp().