Last Update:
std::filesystem in C++17 In Detail
Table of Contents
On Friday 18th January I’ve pushed another update for the book. This
time I rewrote the whole chapter about std::filesystem
. Please have a
look at what changed and what are the plans.
The book got more than 25 new pages!
std::filesystem
- Chapter Rewrite
The book had a filesystem chapter from the start, but it was concise and didn’t contain much information. From the beginning, the plan was to rewrite it, similarly as with the parallel algorithms chapter.
I hoped to do the work in just a few weeks… maybe even before December. But as in other software development related projects, it’s better to multiply the first estimate by 2…3 :)
That’s why I released a new chapter - CSV reader - before this one. By working on a real project, I could learn more and experiment. I needed that to be able to deliver better content.
The refreshed chapter is now 5x larger than the first version! The whole book contains now 306 pages (56 more than I initially planned :))
To sum up, with this refreshed chapter you’ll see:
- How
std::filesystem
got into the Standard - What the basic types and operations are
- How you can work with the paths
- How to handle errors in
std::filesystem
- How to iterate over a directory
- How to create new directories and files
Here’s the link to the book:
Example - Filtering Files
Here’s an example, where you can pass a path and then use regex
filter
and match the file names.
std::vector<FileEntry> CollectFiles(const fs::path& inPath)
{
std::vector<fs::path> paths;
if (fs::exists(inPath) && fs::is_directory(inPath))
{
std::filesystem::recursive_directory_iterator dirpos{ inPath };
std::copy_if(begin(dirpos), end(dirpos), std::back_inserter(paths),
[](const fs::directory_entry& entry) {
return entry.is_regular_file();
}
);
}
std::vector<FileEntry> files(paths.size());
std::transform(paths.cbegin(), paths.cend(), files.begin(), FileEntry::Create);
return files;
}
int main(int argc, char* argv[])
{
try
{
const fs::path pathToShow{ argc >= 2 ? argv[1] : fs::current_path() };
const std::regex reg(argc >= 3 ? argv[2] : "");
auto files = CollectFiles(pathToShow);
std::sort(files.begin(), files.end());
for (auto& entry : files)
{
const auto strFileName = entry.mPath.filename().string();
if (std::regex_match(strFileName, reg))
std::cout << strFileName << "\tsize: " << entry.mSize << '\n';
}
}
catch (const fs::filesystem_error& err)
{
// ...
}
catch (const std::exception& ex)
{
// ...
}
}
And to hold the info about the files the code uses the following helper structure:
struct FileEntry
{
fs::path mPath;
uintmax_t mSize{ 0 };
static FileEntry Create(const fs::path& filePath) {
return FileEntry{ filePath, fs::file_size(filePath) };
}
friend bool operator < (const FileEntry& a, const FileEntry& b) noexcept {
return a.mSize < b.mSize;
}
};
The code iterates over a directory with recursive_directory_iterator
and then filters out only regular files. Later, the function transforms
that vector of paths into a vector of FileEntry
objects.
When all files are collected the main()
function uses std::regex
to
do the matching.
As a possible optimisation, we can also create a vector of
directory_entries rather than paths. This would allow us to fetch the
files size faster, as direcotry_entry::file_size
is usually cached and
filesystem::file_size
needs another file access.
Interactive Course
I’m happy to announce that thanks to the collaboration with the team
@Educative we published C++17 in Detail as an interactive course!
You can see it… and even preview it for free here:
>> C++17 in Detail: A Deep
Dive
It consists of 200 lessons, many quizzes, code snippets… and what’s best
is that it has more than 120 playgrounds! That means you can compile
and edit code sample directly in the browser… so there’s no need for you
to switch back and forth to some compiler/IDE.
I think that such approach increases your learning experience.
And for those of you who are interesting in that form of learning, you can use this coupon:
CPP-DETAIL-20
Use this coupon to buy the course at a much lower price!
Acknowledgements
Special thanks to JFT, Jacek Galowicz, Michał Czaja, and other reviewers who contributed to the chapter!
Book Mentions
So far the book was mentioned in several places.
-
The book is listed in one of the articles from the Visual C++ Team:
Books on C++17 | Visual C++ Team Blog -
There’s a review at CppDepend blog:
C++ 17 In Detail Book Review – CppDepend Blog (including a little discount) -
And there’s also a GoodReads page:
C++17 in Detail @GoodReads
The Plans
The book is 99% ready!
The remaining parts are related mostly to book polishing and smaller fixes!
For example this week I plan to release a small update for the
std::filesystem
chapter (adding notes about handling file
permissions).
Your Feedback
I appreciate your initial feedback and support! The book has now more than 860 readers (and only six refunds)! That’s not too bad I think :)
Let me know what’s your experience with the book. What would you like to change? What would you like to see more?
Add your feedback/review here:
https://www.goodreads.com/book/show/41447221-c-17-in-detail
You can use this comment site:
https://leanpub.com/cpp17indetail/feedback
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