How to create a collection of stream objects

Question

As most know it's not possible to have a standard collection of references. It's also not possible to copy a stream object.

But what if I want to make a collection (say a std::vector) of stream objects or stream object references?

I know I can wrap the stream object reference in e.g. a structure, but then you either need to implement the complete interface (if you want to use the wrapper directly as a stream, which I would prefer), or use a public getter function and use that everywhere to get the actual stream.

Is there a simpler way? C++11 solutions are okay.

Or a collection of smart pointers if its necessary to destroy them automatically? — nob, Apr 10 '13 at 11:18
@riv It would of course work, but I would rather not unless there is no other way. — Some programmer dude, Apr 10 '13 at 11:18
@juanchopanza I think you hit the nail right on target with that one. — Some programmer dude, Apr 10 '13 at 11:20

score 7 · Accepted Answer · answered Apr 10 '13 at 11:18

7

You can't have a container of references, but you can have a container of std::reference_wrapper. Perhaps you want something like:

std::vector<std::reference_wrapper<stream_type>> v;

You can treat a std::reference_wrapper very much like a reference (in fact, it is implicitly convertible to a reference type), but it has the extra advantage of being an object type.

answered Apr 10 '13 at 11:18

Joseph Mansfield

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Just tested and it works fine. Still have to use the `get` function to get the referenced stream if used directly in e.g. output or input operations, but not when passing to other functions. I can live with that. – Some programmer dude Apr 10 '13 at 11:27

score 0 · Answer 2 · answered Apr 10 '13 at 16:55

You can use non-copyable objects in collections:

// this uses move constructors
std::vector<std::fstream> v {std::fstream{"file1.txt"}, std::fstream{"file2.txt"}};

// this doesn't require the type to even be movable
v.emplace_back("file3.txt");

Although avoiding pointer and reference-like types this way will only work if you don't need to use streams as polymorphic objects.

How to create a collection of stream objects

2 Answers2