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std::filesystem::space

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

#include <cstdint>
#include <filesystem>
#include <iostream>
 
void print_space_info(auto const& dirs, int width = 15)
{
    (std::cout << std::left).imbue(std::locale("en_US.UTF-8"));
    for (const auto s : {"Capacity", "Free", "Available", "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})
            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_space_info(dirs);
}

Possible output:

│ Capacity        │ Free            │ Available       │ Dir
│ 84,417,331,200  │ 24,069,705,728  │ 21,492,748,288  │ /dev/null
│ 84,417,331,200  │ 24,069,705,728  │ 21,492,748,288  │ /tmp
│ 250,321,567,744 │ 37,623,181,312  │ 25,152,159,744  │ /home
│ 0               │ 0               │ 0               │ /proc
│ -1              │ -1              │ -1              │ /null

See also

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

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https://en.cppreference.com/w/cpp/filesystem/space