Writing Files in C++

Here’s the translation of the Go code to C++, with explanations in Markdown format suitable for Hugo:

Writing files in C++ follows similar patterns to the ones we saw earlier for reading.

#include <iostream>
#include <fstream>
#include <vector>
#include <stdexcept>

void check(bool condition) {
    if (!condition) {
        throw std::runtime_error("An error occurred");
    }
}

int main() {
    // To start, here's how to dump a string (or just bytes) into a file.
    std::string content = "hello\ncpp\n";
    std::ofstream file1("/tmp/dat1");
    check(file1.is_open());
    file1 << content;
    file1.close();

    // For more granular writes, open a file for writing.
    std::ofstream file2("/tmp/dat2");
    check(file2.is_open());

    // You can write byte vectors as you'd expect.
    std::vector<char> d2 = {115, 111, 109, 101, 10};
    file2.write(d2.data(), d2.size());
    std::cout << "wrote " << d2.size() << " bytes\n";

    // Writing strings is straightforward.
    std::string s = "writes\n";
    file2.write(s.c_str(), s.size());
    std::cout << "wrote " << s.size() << " bytes\n";

    // Flush writes to ensure they're written to stable storage.
    file2.flush();

    // C++ provides buffered writers through std::ofstream.
    // The buffer is automatically managed.
    file2 << "buffered\n";
    std::cout << "wrote 9 bytes\n";

    // The file is automatically closed when file2 goes out of scope.
    // You can also explicitly close it:
    file2.close();

    return 0;
}

Try running the file-writing code.

$ g++ writing-files.cpp -o writing-files
$ ./writing-files
wrote 5 bytes
wrote 7 bytes
wrote 9 bytes

Then check the contents of the written files.

$ cat /tmp/dat1
hello
cpp
$ cat /tmp/dat2
some
writes
buffered

Next, we’ll look at applying some of the file I/O ideas we’ve just seen to the stdin and stdout streams.

Random Numbers in C++

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Writing Files in C++