std::filesystem::space_info(3)

NAME
std::filesystem::space_info - std::filesystem::space_info

Synopsis
   Defined in header <filesystem>
   struct space_info {
   std::uintmax_t capacity;
   std::uintmax_t free; (since C++17)
   std::uintmax_t available;
   };
   Represents the filesystem information as determined by filesystem::space.

Member objects
   capacity total size of the filesystem, in bytes
             (public member object)
   free free space on the filesystem, in bytes
             (public member object)
             free space available to a non-privileged process (may be equal or less
   available than free)
             (public member object)

Non-member functions
   operator== compares two space_infos
   (C++20) (function) operator==(std::filesystem::space_info)
   friend bool operator==( const space_info&, const space_info& ) = (since C++20)
   default;
   Checks if capacity, free and available of both arguments are equal respectively.
   This function is not visible to ordinary unqualified or qualified lookup, and can
   only be found by argument-dependent lookup when std::filesystem::space_info is an
   associated class of the arguments.
   The != operator is synthesized from operator==.

Example
// Run this code
 #include <iostream>
 #include <filesystem>
 #include <cstdint>
 void print_space_info(auto const& dirs, int width = 14)
 {
     std::cout << std::left;
     for (const auto s : {"Capacity", "Free", "Available", "Dir"})
         std::cout << "│ " << std::setw(width) << s << ' ';
     std::cout << '\n';
     std::error_code ec;
     for (auto const& dir : dirs) {
         const std::filesystem::space_info si = std::filesystem::space(dir, ec);
         std::cout
             << "│ " << std::setw(width) << static_cast<std::intmax_t>(si.capacity) << ' '
             << "│ " << std::setw(width) << static_cast<std::intmax_t>(si.free) << ' '
             << "│ " << std::setw(width) << static_cast<std::intmax_t>(si.available) << ' '
             << "│ " << dir << '\n';
     }
 }
 int main()
 {
     const auto dirs = { "/dev/null", "/tmp", "/home", "/null" };
     print_space_info(dirs);
 }

Possible output:
 │ Capacity │ Free │ Available │ Dir
 │ 8342851584 │ 8342851584 │ 8342851584 │ /dev/null
 │ 12884901888 │ 3045265408 │ 3045265408 │ /tmp
 │ 250321567744 │ 37623181312 │ 25152159744 │ /home
 │ -1 │ -1 │ -1 │ /null

See also
   space determines available free space on the file system
   (C++17) (function)