Writing Files

C++ uses std::ofstream (output file stream) to write data to files. Managing open modes (like append or binary) and controlling stream buffering are crucial for writing high-performance C++ code.

std::endl vs. '\n'

In loop-heavy file operations, developers often use std::endl to write newlines. However, std::endl does two things:

• Writes a newline character (' ') to the stream.
• Forcibly flushes the stream's internal buffer to the disk.

Explicitly flushing the buffer on every line bypasses the OS buffering layer, resulting in expensive system calls. Using ' ' writes the newline and lets the stream buffer handle flushes automatically, improving performance by up to 10x.

Code Walkthrough

Demonstrates writing a text log in append mode and writing raw binary data.

#include <iostream>
#include <fstream>
void writeLog(const std::string& logMessage) {
    // Open in append mode (std::ios::app)
    std::ofstream logFile("app.log", std::ios::out | std::ios::app);
if (logFile.is_open()) {
        logFile << "[INFO] " << logMessage << '\n'; // Fast: no force-flush
    }
}
void writeBinaryData() {
    int data[5] = {10, 20, 30, 40, 50};
// Open in binary mode (std::ios::binary)
    std::ofstream outFile("data.bin", std::ios::out | std::ios::binary);
if (outFile.is_open()) {
        // Cast array to char* and specify size in bytes
        outFile.write(reinterpret_cast<const char*>(data), sizeof(data));
    }
}
int main() {
    writeLog("Application started.");
    writeBinaryData();
    return 0;
}

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