std::uintmax_t file_size() const;
std::uintmax_t file_size( std::error_code& ec ) const noexcept;
(since C++17)

If the file size is cached in this directory_entry, returns the cached value. Otherwise, returns std::filesystem::file_size(path()) or std::filesystem::file_size(path(), ec), respectively


[edit] Parameters

ec - out-parameter for error reporting in the non-throwing overload

[edit] Return value

The size of the referred-to filesystem object

[edit] Exceptions

The overload that does not take a std::error_code& parameter throws 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. The overload taking a std::error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur. Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

[edit] Example

The program below prints out the files in given directory alongside with their sizes in human readable form.

#include <filesystem>
#include <iostream>
#include <cstdint>
#include <cmath>
struct HumanReadable {
    uintmax_t size {};
    template <typename Os> friend Os& operator<< (Os& os, HumanReadable hr)
        int i{};
        double mantissa = hr.size;
        for (; mantissa >= 1024.; ++i) {
            mantissa /= 1024.;
        mantissa = std::ceil(mantissa * 10.) / 10.;
        os << mantissa << "BKMGTPE"[i];
        return i == 0 ? os : os << "B (" << hr.size << ')';
int main(int argc, const char* argv[])
    namespace fs = std::filesystem;
    const auto dir = argc == 2 ? fs::path { argv[1] } : fs::current_path();
    for (fs::directory_entry const& entry : fs::directory_iterator(dir)) {
        if (entry.is_regular_file()) {
            std::cout << entry.path().filename()
                      << " size: " << HumanReadable{entry.file_size()} << "\n";

Possible output:

"boost_1_73_0.tar.bz2" size: 104.2MB (109247910)
"CppCon 2018 - Jon Kalb “Copy Elision”.mp4" size: 15.7MB (16411990)
"cppreference-doc-20190607.tar.xz" size: 6.3MB (6531336)
"hana.hpp" size: 6.7KB (6807)

[edit] See also

returns the size of a file
(function) [edit]