C++ vector of pairs initialization - compilation error - c++

Question

I would like to initalize a vector of pairs with some hard-coded values, I tried using different solutions but I keep getting compilation error. My code looks like this:
std::vector<std::pair<cv::HOGDescriptor, std::ifstream> > hogs_files = {
std::make_pair(hog, file),
std::make_pair(hog2, file2),
std::make_pair(hog3, file3),
std::make_pair(hog4, file4),
std::make_pair(hog5, file5),
std::make_pair(hog6, file6),
std::make_pair(hog7, file7),
std::make_pair(hog8, file8)
};
and the error I've got is:
Error C2440 '<function-style-cast>': cannot convert from 'initializer list' to '_Mypair'
Thank you for answers.

Answer 1

The error is because fstreams are not copy-constructible.
I would suggest you move your ifstreams to the vector of pairs; more clarity and control.
std::vector<std::pair<cv::HOGDescriptor, std::ifstream> > hogs_files = {
std::make_pair(hog, std::move(file)),
std::make_pair(hog2, std::move(file2)),
std::make_pair(hog3, std::move(file3)),
std::make_pair(hog4, std::move(file4)),
std::make_pair(hog5, std::move(file5)),
std::make_pair(hog6, std::move(file6)),
std::make_pair(hog7, std::move(file7)),
std::make_pair(hog8, std::move(file8))
};

Answer 2

The general approach to initialize the vector of pairs is OK but the problem is that std::ifstream is not copy-constructible. Hence, you won't be able to use
std::vector<std::pair<cv::HOGDescriptor, std::ifstream> > hogs_files = {
std::make_pair(hog, file),
...
};
However, you should be able to use std::ifstream* in the pair:
std::vector<std::pair<cv::HOGDescriptor, std::ifstream*> > hogs_files = {
std::make_pair(hog, &file),
...
};