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Showing content from https://github.com/gulrak/filesystem/tree/v1.4.0 below:

GitHub - gulrak/filesystem at v1.4.0

This is a header-only single-file std::filesystem compatible helper library, based on the C++17 and C++20 specs, but implemented for C++11, C++14, C++17 or C++20 (tightly following the C++17 standard with very few documented exceptions). It is currently tested on macOS 10.12/10.14/10.15, Windows 10, Ubuntu 18.04, CentOS 7, CentOS 8, FreeBSD 12 and Alpine ARM/ARM64 Linux but should work on other systems too, as long as you have at least a C++11 compatible compiler. It should work with Android NDK, Emscripten and I even had reports of it being used on iOS (within sandboxing constraints). It is of course in its own namespace ghc::filesystem to not interfere with a regular std::filesystem should you use it in a mixed C++17 environment (which is possible).

Test coverage is well above 90%, and starting with v1.3.6 more time was invested in benchmarking and optimizing parts of the library. I'll try to continue to optimize some parts and refactor others, striving to improve it as long as it doesn't introduce additional C++17/C++20 compatibility issues. Feedback is always welcome. Simply open an issue if you see something missing or wrong or not behaving as expected and I'll comment.

I'm often in need of filesystem functionality, mostly fs::path, but directory access too, and when beginning to use C++11, I used that language update to try to reduce my third-party dependencies. I could drop most of what I used, but still missed some stuff that I started implementing for the fun of it. Originally I based these helpers on my own coding- and naming conventions. When C++17 was finalized, I wanted to use that interface, but it took a while, to push myself to convert my classes.

The implementation is closely based on chapter 30.10 from the C++17 standard and a draft close to that version is Working Draft N4687. It is from after the standardization of C++17 but it contains the latest filesystem interface changes compared to the Working Draft N4659. Staring with v1.4.0, when compiled using C++20, it adapts to the changes according to path sorting order and std::u8string handling from Working Draft N4680.

I want to thank the people working on improving C++, I really liked how the language evolved with C++11 and the following standards. Keep on the good work!

If you ask yourself, what ghc is standing for, it is simply gulraks helper classes, yeah, I know, not very imaginative, but I wanted a short namespace and I use it in some of my private classes (so it has nothing to do with Haskell, sorry for the name clash).

ghc::filesystem is developed on macOS but CI tested on macOS, Windows, various Linux Distributions and FreeBSD. It should work on any of these with a C++11-capable compiler. Also there are some checks to hopefully better work on Android, but as I currently don't test with the Android NDK, I wouldn't call it a supported platform yet, same is valid for using it with Emscripten. It is now part of the detected platforms, I fixed the obvious issues and ran some tests with it, so it should be fine. All in all, I don't see it replacing std::filesystem where full C++17 or C++20 is available, it doesn't try to be a "better" std::filesystem, just an almost drop-in if you can't use it (with the exception of the UTF-8 preference).

This implementation is following the "UTF-8 Everywhere" philosophy in that all std::string instances will be interpreted the same as std::u8string encoding wise and as being in UTF-8. The std::u16string will be seen as UTF-16. See Differences in API for more information.

Unit tests are currently run with:

The header comes with a set of unit-tests and uses CMake as a build tool and Catch2 as test framework.

All tests agains this implementation should succeed, depending on your environment it might be that there are some warnings, e.g. if you have no rights to create Symlinks on Windows or at least the test thinks so, but these are just informative.

To build the tests from inside the project directory under macOS or Linux just:

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Debug ..
make

This generates filesystem_test, the binary that runs all tests.

If the default compiler is a GCC 8 or newer, or Clang 7 or newer, it additionally tries to build a version of the test binary compiled against GCCs/Clangs std::filesystem implementation, named std_filesystem_test as an additional test of conformance. Ideally all tests should compile and succeed with all filesystem implementations, but in reality, there are some differences in behavior, sometimes due to room for interpretation in in the standard, and there might be issues in these implementations too.

The latest release version is v1.4.0 and source archives can be found here.

The latest pre-C++20 release version is v1.3.10 and source archives can be found here.

Using it as Single-File-Header

As ghc::filesystem is at first a header-only library, it should be enough to copy the header or the include/ghc directory into your project folder oder point your include path to this place and simply include the filesystem.hpp header (or ghc/filesystem.hpp if you use the subdirectory).

Everything is in the namespace ghc::filesystem, so one way to use it only as a fallback could be:

#if ((defined(_MSVC_LANG) && _MSVC_LANG >= 201703L) || (defined(__cplusplus) && __cplusplus >= 201703L)) && defined(__has_include)
#if __has_include(<filesystem>) && (!defined(__MAC_OS_X_VERSION_MIN_REQUIRED) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 101500)
#define GHC_USE_STD_FS
#include <filesystem>
namespace fs = std::filesystem;
#endif
#endif
#ifndef GHC_USE_STD_FS
#include <ghc/filesystem.hpp>
namespace fs = ghc::filesystem;
#endif

Note that this code uses a two-stage preprocessor condition because Visual Studio 2015 doesn't like the (<...>) syntax, even if it could cut evaluation early before. This code also used the minimum deployment target to detect if std::filesystem really is available on macOS compilation.

Note also, this detection now works on MSVC versions prior to 15.7 on, or without setting the /Zc:__cplusplus compile switch that would fix __cplusplus on MSVC. (Without the switch the compiler allways reports 199711L (see), but _MSVC_LANG works without it.

If you want to also use the fstream wrapper with path support as fallback, you might use:

#if ((defined(_MSVC_LANG) && _MSVC_LANG >= 201703L) || (defined(__cplusplus) && __cplusplus >= 201703L)) && defined(__has_include)
#if __has_include(<filesystem>) && (!defined(__MAC_OS_X_VERSION_MIN_REQUIRED) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 101500)
#define GHC_USE_STD_FS
#include <filesystem>
namespace fs {
using namespace std::filesystem;
using ifstream = std::ifstream;
using ofstream = std::ofstream;
using fstream = std::fstream;
}
#endif
#endif
#ifndef GHC_USE_STD_FS
#include <ghc/filesystem.hpp>
namespace fs {
using namespace ghc::filesystem;
using ifstream = ghc::filesystem::ifstream;
using ofstream = ghc::filesystem::ofstream;
using fstream = ghc::filesystem::fstream;
} 
#endif

Now you have e.g. fs::ofstream out(somePath); and it is either the wrapper or the C++17 std::ofstream.

Be aware, as a header-only library, it is not hiding the fact, that it uses system includes, so they "pollute" your global namespace.

ℹ️ Hint: There is an additional header named ghc/fs_std.hpp that implements this dynamic selection of a filesystem implementation, that you can include instead of ghc/filesystem.hpp when you want std::filesystem where available and ghc::filesystem where not. It also enables the wchar_t support on ghc::filesystem on Windows, so the resulting implementation in the fs namespace will be compatible.

Using it as Forwarding-/Implementation-Header

Alternatively, starting from v1.1.0 ghc::filesystem can also be used by including one of two additional wrapper headers. These allow to include a forwarded version in most places (ghc/fs_fwd.hpp) while hiding the implementation details in a single cpp that includes ghc/fs_impl.hpp to implement the needed code. That way system includes are only visible from inside the cpp, all other places are clean.

Be aware, that it is currently not supported to hide the implementation into a Windows-DLL, as a DLL interface with C++ standard templates in interfaces is a different beast. If someone is willing to give it a try, I might integrate a PR but currently working on that myself is not a priority.

If you use the forwarding/implementation approach, you can still use the dynamic switching like this:

#if ((defined(_MSVC_LANG) && _MSVC_LANG >= 201703L) || (defined(__cplusplus) && __cplusplus >= 201703L)) && defined(__has_include)
#if __has_include(<filesystem>) && (!defined(__MAC_OS_X_VERSION_MIN_REQUIRED) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 101500)
#define GHC_USE_STD_FS
#include <filesystem>
namespace fs {
using namespace std::filesystem;
using ifstream = std::ifstream;
using ofstream = std::ofstream;
using fstream = std::fstream;
}
#endif
#endif
#ifndef GHC_USE_STD_FS
#include <ghc/fs-fwd.hpp>
namespace fs {
using namespace ghc::filesystem;
using ifstream = ghc::filesystem::ifstream;
using ofstream = ghc::filesystem::ofstream;
using fstream = ghc::filesystem::fstream;
} 
#endif

and in the implementation hiding cpp, you might use (before any include that includes ghc/fs_fwd.hpp to take precedence:

#if ((defined(_MSVC_LANG) && _MSVC_LANG >= 201703L) || (defined(__cplusplus) && __cplusplus >= 201703L)) && defined(__has_include)
#if __has_include(<filesystem>) && (!defined(__MAC_OS_X_VERSION_MIN_REQUIRED) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 101500)
#define GHC_USE_STD_FS
#endif
#endif
#ifndef GHC_USE_STD_FS
#define GHC_FILESYSTEM_IMPLEMENTATION
#include <ghc/filesystem.hpp>
#endif

ℹ️ Hint: There are additional helper headers, named ghc/fs_std_fwd.hpp and ghc/fs_std_impl.hpp that use this technique, so you can simply include them if you want to dynamically select the filesystem implementation. they also enable the wchar_t support on ghc::filesystem on Windows, so the resulting implementation in the fs namespace will be compatible.

Starting from v1.1.0, it is possible to add ghc::filesystem as a git submodule, add the directory to your CMakeLists.txt with add_subdirectory() and then simply use target_link_libraries(your-target ghc_filesystem) to ensure correct include path that allow #include <ghc/filesystem.hpp> to work.

The CMakeLists.txt offers a few options to customize its behaviour:

There is a version macro GHC_FILESYSTEM_VERSION defined in case future changes might make it needed to react on the version, but I don't plan to break anything. It's the version as decimal number (major * 10000 + minor * 100 + patch).

Note: Starting from v1.0.2 only even patch versions will be used for releases and odd patch version will only be used for in between commits while working on the next version.

There is almost no documentation in this release, as any std::filesystem documentation would work, besides the few differences explained in the next section. So you might head over to https://en.cppreference.com/w/cpp/filesystem for a description of the components of this library.

When compiling with C++11, C++14 or C++17, the API is following the C++17 standard, where possible, with the exception that std::string_view parameters are only supported on C++17. When Compiling with C++20, ghc::filesysytem defaults to the C++20 API, with the char8_t and std::u8string interfaces and the deprecated fs::u8path factory method.

Note: If the C++17 API should be enforced even in C++20 mode, use the define GHC_FILESYSTEM_ENFORCE_CPP17_API. Even then it is possible to create fws::path from std::u8string but fs::path::u8string() and fs::path::generic_u8string() return normal UTF-8 encoded std::string instances, so code written for C++17 could still work with ghc::filesystem when compiled with C++20.

The only additions to the standard are documented here:

ghc::filesystem::ifstream, ghc::filesystem::ofstream, ghc::filesystem::fstream

These are simple wrappers around std::ifstream, std::ofstream and std::fstream. They simply add an open() method and a constuctor with an ghc::filesystem::path argument as the fstream variants in C++17 have them.

ghc::filesystem::u8arguments

This is a helper class that currently checks for UTF-8 encoding on non-Windows platforms but on Windows it fetches the command line arguments als Unicode strings from the OS with

::CommandLineToArgvW(::GetCommandLineW(), &argc)

and then converts them to UTF-8, and replaces argc and argv. It is a guard-like class that reverts its changes when going out of scope.

So basic usage is:

namespace fs = ghc::filesystem;

int main(int argc, char* argv[])
{
    fs::u8arguments u8guard(argc, argv);
    if(!u8guard.valid()) {
        std::cerr << "Bad encoding, needs UTF-8." << std::endl;
        exit(EXIT_FAILURE);
    }

    // now use argc/argv as usual, they have utf-8 enconding on windows
    // ...

    return 0;
}

That way argv is UTF-8 encoded as long as the scope from main is valid.

Note: On macOS, while debugging under Xcode the code currently will return false as Xcode starts the application with US-ASCII as encoding, no matter what encoding is actually used and even setting LC_ALL in the product scheme doesn't change anything. I still need to investigate this.

As this implementation is based on existing code from my private helper classes, it derived some constraints of it, leading to some differences between this and the standard C++17/C++20 API.

This implementation has switchable behavior for the LWG defects #2682, #2935, #2936 and #2937. The currently selected behavior (starting from v1.4.0) is following #2682, #2936, #2937 but not following #2935, as I feel it is a bug to report no error on a create_directory() or create_directories() where a regular file of the same name prohibits the creation of a directory and forces the user of those functions to double-check via fs::is_directory if it really worked. The more intuitive approach to directory creation of treating a file with that name as an error is also advocated by the newer paper WG21 P1164R0, the revison P1161R1 was agreed upon on Kona 2019 meeting see merge and GCC by now switched to following its proposal (GCC #86910).

Not Implemented on C++ before C++17 
// methods in ghc::filesystem::path:
path& operator+=(basic_string_view<value_type> x);
int compare(basic_string_view<value_type> s) const;

These are not implemented under C++11 and C++14, as there is no std::basic_string_view available and I did want to keep this implementation self-contained and not write a full C++17-upgrade for C++11/14. Starting with v1.1.0 these are supported when compiling ghc::filesystem under C++17.

To not depend on any external third party libraries and still stay portable and compact, this implementation is following the "UTF-8 Everywhere" philosophy in that all std::string instances will be interpreted the same as std::u8string encoding wise and as being in UTF-8. The std::u16string will be seen as UTF-16 and std::u32string will be seen as unicode codepoints. Depending on the size of std::wstring characters, it will handle std::wstring as being UTF-16 (e.g. Windows) or char32_t unicode codepoints (currently all other platforms).

Differences of Specific Interfaces 
filesystem::path::string_type
filesystem::path::value_type

In Windows, an implementation should use std::wstring and wchar_t as types used for the native representation, but as I'm a big fan of the "UTF-8 Everywhere" philosophy, I decided agains it for now. If you need to call some Windows API, use the W-variant with the path::wstring() member (e.g. GetFileAttributesW(p.wstring().c_str())). This gives you the Unicode variant independant of the UNICODE macro and makes sharing code between Windows, Linux and macOS easier.

Starting with v1.2.0 ghc::filesystem has the option to select the more standard conforming APi with wchar_t and std::wstring on Windows by defining GHC_WIN_WSTRING_STRING_TYPE. This define has no effect on other platforms and will be set by the helping headers ghc/fs_std.hpp and the pair ghc/fs_std_fwd.hpp/ghc/fs_std_impl.hpp to enhance compatibility.

const path::string_type& path::native() const /*noexcept*/;
const path::value_type *path::c_str() const /*noexcept*/;

These two can not be noexcept with the current implementation. This due to the fact, that internally path is working on the generic path version only, and the getters need to do a conversion to native path format.

const path::string_type& path::generic_string() const;

This returns a const reference, instead of a value, because it can. This implementation uses the generic representation for internal workings, so it's "free" to return that.

std::string path::u8string() const;
std::string path::generic_u8string() const;
vs.
std::u8string path::u8string() const;
std::u8string path::generic_u8string() const;

The return type of these two methods is depending on the used C++ standard and if GHC_FILESYSTEM_ENFORCE_CPP17_API is defined. On C++11, C++14 and C++17 or when GHC_FILESYSTEM_ENFORCE_CPP17_API is defined, the return type is std::string, and on C++20 without the define it is std::u8string.

I created a wiki entry about quite a lot of behavioral differences between different std::filesystem implementations that could result in a mention here, but this readme only tries to address the design choice differences between ghc::filesystem and those. I try to update the wiki page from time to time.

Any additional observations are welcome!

As the complete inner mechanics of this implementation fs::path are working on the generic format, it is the internal representation. So creating any mixed slash fs::path object under Windows (e.g. with "C:\foo/bar") will lead to a unified path with "C:\foo\bar" via native() and "C:/foo/bar" via generic_string() API.

Additionally this implementation follows the standards suggestion to handle posix paths of the form "//host/path" and USC path on windows also as having a root-name (e.g. "//host"). The GCC implementation didn't choose to do that while testing on Ubuntu 18.04 and macOS with GCC 8.1.0 or Clang 7.0.0. This difference will show as warnings under std::filesystem. This leads to a change in the algorithm described in the standard for operator/=(path& p) where any path p with p.is_absolute() will degrade to an assignment, while this implementation has the exception where *this == *this.root_name() and p == preferred_seperator a normal append will be done, to allow:

fs::path p1 = "//host/foo/bar/file.txt";
fs::path p2;
for (auto p : p1) p2 /= p;
ASSERT(p1 == p2);

For all non-host-leading paths the behaviour will match the one described by the standard.

Then there is fs::copy. The tests in the suite fail partially with C++17 std::filesystem on GCC/Clang. They complain about a copy call with fs::copy_options::recursive combined with fs::copy_options::create_symlinks or fs::copy_options::create_hard_links if the source is a directory. There is nothing in the standard that forbids this combination and it is the only way to deep-copy a tree while only create links for the files. There is LWG #2682 that supports this interpretation, but the issue ignores the usefulness of the combination with recursive and part of the justification for the proposed solution is "we did it so for almost two years". But this makes fs::copy with fs::copy_options::create_symlinks or fs::copy_options::create_hard_links just a more complicated syntax for the fs::create_symlink or fs::create_hardlink operation and I don't want to believe, that this was the intention of the original writing. As there is another issue related to copy, with a different take on the description.

Note: With v1.1.2 I decided to integrate a behavior switch for this and make the LWG #2682 the default.

There are still some methods that break the noexcept clause, some are related to LWG defects, some are due to my implementation. I work on fixing the later ones, and might in cases where there is no way of implementing the feature without risk of an exception, break conformance and remove the noexcept.

Symbolic Links on Windows

As symbolic links on Windows, while being supported more or less since Windows Vista (with some strict security constraints) and fully since some earlier build of Windows 10, when "Developer Mode" is activated, are at time of writing (2018) rarely used, still they are supported with this implementation.

The Windows ACL permission feature translates badly to the POSIX permission bit mask used in the interface of C++17 filesystem. The permissions returned in the file_status are therefore currently synthesized for the user-level and copied to the group- and other-level. There is still some potential for more interaction with the Windows permission system, but currently setting or reading permissions with this implementation will most certainly not lead to the expected behavior.

This was the first public release version. It implements the full range of C++17 std::filesystem, as far as possible without other C++17 dependencies.

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