simple boinary file write tests C++

gistfile1.txt

#include <iostream>
#include <fstream> 
#include <vector>
int main()
{
    std::fstream f;
    std::string filePath = "file.txt";

    f.open(filePath, std::ios_base::binary  | std::ios_base::out | std::ios_base::in | std::ios_base::trunc );
    if (!f.is_open()) {
        std::cout << "ERROR, file not open" << std::endl;
        return 1;
    }
    //Write some data to vector
    std::vector<char> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);
    v.push_back(4);
    v.push_back(5);
    //Go to beggining of the file to write
    f.seekg(0, std::ios::beg);
    f.seekp(0, std::ios::beg);
    //Write the vector to file
    f.write(v.data(), v.size());
    f.flush();
    //Lets read so we see that things were written to the file
    //Don't know why I've put clear, but won't work without it too
    //f.clear();
    f.seekg(0, std::ios::beg);
    f.seekp(0, std::ios::beg);
    auto v2 = std::vector<char>(v.size());
    //Read things back to file
    f.read(v2.data(), v2.size());
    if (f) {
        std::cout << "did read everything" << std::endl;
    } else {
        std::cout << "did read only " << f.gcount() << " bytes" << std::endl;
    }
    f.close();
    
    return 0;
}