Got error C2280 when using std::vector.push_back()

Question

I got error "C2280: attempting to reference a deleted function" compiling error when doing following code:

std::ofstream ofs(m_headerFileName, std::ios::binary, std::ios_base::app);
            m_ofsHeader.push_back(ofs);

where

std::vector<std::ofstream>      m_ofsHeader;

I don't understand why I cannot push a ofstream instance into an ofstream vector . Someone gives some hint? Thanks. I am on Windows 7 and Visual Studio 2015. Also, what is the walkaround here if there is any?

I am trying to keep a bunch of ifstream/ofstream with each one having their own file to read/write.

Answer 1

Streams have no copy constructor. You might implement your own or possibly move semantics.

Answer 2

First of all, the following is wrong, because there is no std::ofstream constructor taking three arguments:

 std::ofstream ofs(m_headerFileName, std::ios::binary, std::ios_base::app); 

You probably meant:

std::ofstream ofs(m_headerFileName, std::ios::binary | std::ios::app)

And then, there's the storage problem. Streams cannot be copied, that's why your push_back fails.

You could just move the streams instead:

#include <fstream>
#include <vector>
#include <ios>

int main()
{
    std::vector<std::ofstream> streams;

    std::ofstream os("foo.txt", std::ios::binary | std::ios::app);
    streams.push_back(std::move(os));
}

Note the std::move , which casts os so that the && overload of push_back is used.

Or you store std::unique_ptr s to the streams in the vector:

#include <fstream>
#include <memory>
#include <vector>
#include <ios>

int main()
{
    std::vector<std::unique_ptr<std::ofstream>> streams;

    auto os = std::make_unique<std::ofstream>("foo.txt", std::ios::binary | std::ios::app);
    streams.push_back(std::move(os));
}

Answer 3

Streams cannot be copied. Their copy constructor and copy assigner are mark as delete . Consider using move semantics as well as std::vector::emplace_back() :

m_ofsHeader.emplace_back(std::move(ofs));
            ^~~~~~~      ^~~~