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std::filesystem::directory_entry::file_size

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.

Parameters

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

Return value

The size of the referred-to filesystem object.

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.

Example

Prints the list of files in a given directory alongside with their sizes in human readable form.

#include <filesystem>
#include <iostream>
#include <cstdint>
#include <cmath>
 
struct HumanReadable {
    std::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[])
{
    const auto dir = argc == 2 ? std::filesystem::path{ argv[1] }
                               : std::filesystem::current_path();
 
    for (std::filesystem::directory_entry const& entry : 
         std::filesystem::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)

See also

(C++17)
 returns the size of a file
(function)

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https://en.cppreference.com/w/cpp/filesystem/directory_entry/file_size