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    std::filesystem::space

    From cppreference.com
     
    C++
     
    Filesystem library
    Classes
    Functions
    File types
     
    Defined in header <filesystem>
    std::filesystem::space_info space( const std::filesystem::path& p );
    		 (1) (since C++17)
    std::filesystem::space_info space( const std::filesystem::path& p, std::error_code& ec ) noexcept;
    		 (2) (since C++17)

    Determines the information about the filesystem on which the pathname p is located, as if by POSIX statvfs.

    Populates and returns an object of type filesystem::space_info, set from the members of the POSIX struct statvfs as follows:

    The non-throwing overload sets all members to static_cast<std::uintmax_t>(-1) on error.

    Parameters

    p - path to examine
    ec - out-parameter for error reporting in the non-throwing overload

    Return value

    The filesystem information (a filesystem::space_info object).

    Exceptions

    Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

    1) Throws std::filesystem::filesystem_error on underlying OS API errors, constructed with p as the first path argument and the OS error code as the error code argument.
    2) Sets a std::error_code& parameter to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur.

    Notes

    space_info.available may be less than space_info.free.

    Example

    Run this code
    #include <cstdint>
#include <filesystem>
#include <iostream>
#include <locale>

std::uintmax_t disk_usage_percent(const std::filesystem::space_info& si,
                                  bool is_privileged = false) noexcept
{
    if (constexpr std::uintmax_t X(-1);
        si.capacity == 0 || si.free == 0 || si.available == 0 ||
        si.capacity == X || si.free == X || si.available == X
    )
        return 100;

    std::uintmax_t unused_space = si.free, capacity = si.capacity;
    if (!is_privileged)
    {
        const std::uintmax_t privileged_only_space = si.free - si.available;
        unused_space -= privileged_only_space;
        capacity -= privileged_only_space;
    }
    const std::uintmax_t used_space{capacity - unused_space};
    return 100 * used_space / capacity;
}

void print_disk_space_info(auto const& dirs, int width = 14)
{
    (std::cout << std::left).imbue(std::locale("en_US.UTF-8"));

    for (const auto s : {"Capacity", "Free", "Available", "Use%", "Dir"})
        std::cout << "│ " << std::setw(width) << s << ' ';

    for (std::cout << '\n'; auto const& dir : dirs)
    {
        std::error_code ec;
        const std::filesystem::space_info si = std::filesystem::space(dir, ec);
        for (auto x : {si.capacity, si.free, si.available, disk_usage_percent(si)})
            std::cout << "│ " << std::setw(width) << static_cast<std::intmax_t>(x) << ' ';
        std::cout << "│ " << dir << '\n';
    }
}

int main()
{
    const auto dirs = {"/dev/null", "/tmp", "/home", "/proc", "/null"};
    print_disk_space_info(dirs);
}

    Possible output: 

    │ Capacity       │ Free           │ Available      │ Use%           │ Dir            
│ 84,417,331,200 │ 42,732,986,368 │ 40,156,028,928 │ 50             │ /dev/null
│ 84,417,331,200 │ 42,732,986,368 │ 40,156,028,928 │ 50             │ /tmp
│ -1             │ -1             │ -1             │ 100            │ /home
│ 0              │ 0              │ 0              │ 100            │ /proc
│ -1             │ -1             │ -1             │ 100            │ /null

    See also

    (C++17)
    		 information about free and available space on the filesystem
    (class) [edit]