Reading and writing a std::vector into a file correctly with iterators

Question

I\'m trying to understand the answer provided here, but I can\'t seem to make it work.

Here is what I\'ve tried:

#include 
#include          


        

Answer 1

The file is not ready to be read by the time the second copy is called. (Thanks to Piotr Skotnicki for his answer in the comments)

A call to flush allows the program to work:

#include 
#include 
#include 
#include 
#include 

int main()
{
    std::string path("numbersfile");

    std::vector myVector{1,16,32,64};
    std::vector newVector{};

    std::ofstream FILE(path,std::ios::out | std::ofstream::binary);
    std::copy(myVector.begin(),myVector.end(),std::ostreambuf_iterator(FILE));
    FILE.flush(); // required here

    std::ifstream INFILE(path,std::ios::in | std::ifstream::binary);
    std::istreambuf_iterator iter(INFILE);
    //std::copy(iter.begin(),iter.end(),std::back_inserter(newVector)); //this doesn't compile
    std::copy(iter,std::istreambuf_iterator{},std::back_inserter(newVector)); // this leaves newVector empty
    return 0;
}

The ofstream is still in scope when the ifstream is created. Had the ofstream's destructor been called then the file would also have been ready for the ifstream. In the following program the ifstream is automatically destructed:

#include 
#include 
#include 
#include 

std::string filename("numbersfile");

std::vector myVector{1.342, 16.33, 32.1, 12364};

void write_vector_to_file(const std::vector& myVector, std::string filename);
std::vector read_vector_from_file(std::string filename);

int main()
{
    write_vector_to_file(myVector, filename);
    auto newVector{read_vector_from_file(filename)};
    return 0;
}

void write_vector_to_file(const std::vector& myVector, std::string filename)
{
    std::ofstream ofs(filename, std::ios::out | std::ofstream::binary);
    std::ostream_iterator osi{ofs," "};
    std::copy(myVector.begin(), myVector.end(), osi);
}

std::vector read_vector_from_file(std::string filename)
{
    std::vector newVector{};
    std::ifstream ifs(filename, std::ios::in | std::ifstream::binary);
    std::istream_iterator iter{ifs};
    std::istream_iterator end{};
    std::copy(iter, end, std::back_inserter(newVector));
    return newVector;
}