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How can I get a file's size in C++ in 2019 with C++ 17?

How can I get a file's size in C++?tellg() function give wrong size of file?Fstream's tellg / seekg returning higher value than expectedHow can I determine the current size of the file opened by std::ofstream?how to get the filesize for large files in c++What are some resources for getting started in operating system development?How can I safely create a nested directory?How can I profile C++ code running on Linux?What is an application binary interface (ABI)?What are the basic rules and idioms for operator overloading?How can I get a file's size in C++?C++11 introduced a standardized memory model. What does it mean? And how is it going to affect C++ programming?Image Processing: Algorithm Improvement for 'Coca-Cola Can' RecognitionWhen should I really use noexcept?Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations

13

3

How can I get a file's size in C++ with modern technologies as they are available in 2019 with C++ 17?

Are there pitfalls for specific operating systems, I should know of?

There are many duplicates (1, 2, 3, 4, 5) of this question but they were answered decades ago. The very high voted answers in many of these questions are wrong today.

c++ operating-system c++17 filesize

share|improve this question

edited 9 hours ago

Jonas Stein

asked 10 hours ago

Jonas SteinJonas Stein

2,47655 gold badges2727 silver badges5757 bronze badges

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Starter for 10: en.cppreference.com/w/cpp/header/filesystem
  
  – Richard Critten
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Possible duplicate of How can I determine the current size of the file opened by std::ofstream?
  
  – Ted Lyngmo
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How, exactly, do those answers go wrong?
  
  – L. F.
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @L.F.: Well, the first question has been closed as a duplicate of the second, which explains why the accepted answer in the first is wrong. The third one is asking about similar tellg problems. The only one worth bothering with is the fourth one, and that one's not great, since it talks too much about ofstream, in both the question and its answers. This one is far better at expressing the intent than the others (except for the first, which is oddly closed).
  
  – Nicol Bolas
  1 hour ago
  
  
  

  
  
  
  

add a comment | 

13

3

How can I get a file's size in C++ with modern technologies as they are available in 2019 with C++ 17?

Are there pitfalls for specific operating systems, I should know of?

There are many duplicates (1, 2, 3, 4, 5) of this question but they were answered decades ago. The very high voted answers in many of these questions are wrong today.

c++ operating-system c++17 filesize

share|improve this question

edited 9 hours ago

Jonas Stein

asked 10 hours ago

Jonas SteinJonas Stein

2,47655 gold badges2727 silver badges5757 bronze badges

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Starter for 10: en.cppreference.com/w/cpp/header/filesystem
  
  – Richard Critten
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Possible duplicate of How can I determine the current size of the file opened by std::ofstream?
  
  – Ted Lyngmo
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How, exactly, do those answers go wrong?
  
  – L. F.
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @L.F.: Well, the first question has been closed as a duplicate of the second, which explains why the accepted answer in the first is wrong. The third one is asking about similar tellg problems. The only one worth bothering with is the fourth one, and that one's not great, since it talks too much about ofstream, in both the question and its answers. This one is far better at expressing the intent than the others (except for the first, which is oddly closed).
  
  – Nicol Bolas
  1 hour ago
  
  
  

  
  
  
  

add a comment | 

How can I get a file's size in C++ with modern technologies as they are available in 2019 with C++ 17?

Are there pitfalls for specific operating systems, I should know of?

There are many duplicates (1, 2, 3, 4, 5) of this question but they were answered decades ago. The very high voted answers in many of these questions are wrong today.

c++ operating-system c++17 filesize

share|improve this question

edited 9 hours ago

Jonas Stein

asked 10 hours ago

Jonas SteinJonas Stein

2,47655 gold badges2727 silver badges5757 bronze badges

share|improve this question

edited 9 hours ago

Jonas Stein

asked 10 hours ago

Jonas SteinJonas Stein

2,47655 gold badges2727 silver badges5757 bronze badges

share|improve this question

edited 9 hours ago

Jonas Stein

asked 10 hours ago

Jonas SteinJonas Stein

2,47655 gold badges2727 silver badges5757 bronze badges

asked 10 hours ago

Jonas SteinJonas Stein

2,47655 gold badges2727 silver badges5757 bronze badges

asked 10 hours ago

Jonas SteinJonas Stein

2,47655 gold badges2727 silver badges5757 bronze badges

2 Answers
2

active

oldest

votes

18

<filesystem> (added in C++17) makes this very straightforward.

#include <cstdint>

#include <filesystem>



// ...



std::uintmax_t size = std::filesystem::file_size("c:foobar.txt");

share|improve this answer

answered 10 hours ago

HolyBlackCatHolyBlackCat

18.6k33 gold badges3737 silver badges7171 bronze badges

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  Little offtopic: is there a world where std::uintmax_t will be able to hold greater values than std::size_t? If not, why not use std::size_t, which arguably is more recognisable? +1 on the answer, btw
  
  – Fureeish
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  @Fureeish I used just because that's the type file_size returns. Looks slightly weird to me too.
  
  – HolyBlackCat
  10 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  8
  

  
  
  
  
  
  

  
  
  @Fureeish std::size_t is only required to hold the max size of in memory objects. Files can be considerably larger,
  
  – Richard Critten
  10 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @RichardCritten so the answer to the first question of my comment is "yes"?
  
  – Fureeish
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  @Fureeish Well, on 32-bit Windows (and I assume on most modern 32-bit platforms) size_t is 32 bits, and uintmax_t is 64 bits.
  
  – HolyBlackCat
  10 hours ago
  
  
  

  
  
  
  

 | 
show 4 more comments

7

This might help.

#include <chrono>

#include <filesystem>  

#include <iostream>



namespace fs = std::filesystem;



int main(int argc, char* argv[])

{

    try

    {

        const auto fsize = fs::file_size("a.out");

        std::cout << fsize << 'n';

    }

    catch (const fs::filesystem_error& err)

    {

        std::cerr << "filesystem error! " << err.what() << 'n';

        if (!err.path1().empty())

            std::cerr << "path1: " << err.path1().string() << 'n';

        if (!err.path2().empty())

            std::cerr << "path2: " << err.path2().string() << 'n';

    }

    catch (const std::exception& ex)

    {

        std::cerr << "general exception: " << ex.what() << 'n';

    }



    // using error_code

    std::error_code ec{};

    auto size = std::filesystem::file_size("a.out", ec);

    if (ec == std::error_code{})

        std::cout << "size: " << size << 'n';

    else

        std::cout << "error when accessing test file, size is: " 

              << size << " message: " << ec.message() << 'n';

}

share|improve this answer

answered 10 hours ago

GOVIND DIXITGOVIND DIXIT

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18

<filesystem> (added in C++17) makes this very straightforward.

#include <cstdint>

#include <filesystem>



// ...



std::uintmax_t size = std::filesystem::file_size("c:foobar.txt");

share|improve this answer

answered 10 hours ago

HolyBlackCatHolyBlackCat

18.6k33 gold badges3737 silver badges7171 bronze badges

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  Little offtopic: is there a world where std::uintmax_t will be able to hold greater values than std::size_t? If not, why not use std::size_t, which arguably is more recognisable? +1 on the answer, btw
  
  – Fureeish
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  @Fureeish I used just because that's the type file_size returns. Looks slightly weird to me too.
  
  – HolyBlackCat
  10 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  8
  

  
  
  
  
  
  

  
  
  @Fureeish std::size_t is only required to hold the max size of in memory objects. Files can be considerably larger,
  
  – Richard Critten
  10 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @RichardCritten so the answer to the first question of my comment is "yes"?
  
  – Fureeish
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  @Fureeish Well, on 32-bit Windows (and I assume on most modern 32-bit platforms) size_t is 32 bits, and uintmax_t is 64 bits.
  
  – HolyBlackCat
  10 hours ago
  
  
  

  
  
  
  

 | 
show 4 more comments

18

<filesystem> (added in C++17) makes this very straightforward.

#include <cstdint>

#include <filesystem>



// ...



std::uintmax_t size = std::filesystem::file_size("c:foobar.txt");

share|improve this answer

answered 10 hours ago

HolyBlackCatHolyBlackCat

18.6k33 gold badges3737 silver badges7171 bronze badges

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  Little offtopic: is there a world where std::uintmax_t will be able to hold greater values than std::size_t? If not, why not use std::size_t, which arguably is more recognisable? +1 on the answer, btw
  
  – Fureeish
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  @Fureeish I used just because that's the type file_size returns. Looks slightly weird to me too.
  
  – HolyBlackCat
  10 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  8
  

  
  
  
  
  
  

  
  
  @Fureeish std::size_t is only required to hold the max size of in memory objects. Files can be considerably larger,
  
  – Richard Critten
  10 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @RichardCritten so the answer to the first question of my comment is "yes"?
  
  – Fureeish
  10 hours ago
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  @Fureeish Well, on 32-bit Windows (and I assume on most modern 32-bit platforms) size_t is 32 bits, and uintmax_t is 64 bits.
  
  – HolyBlackCat
  10 hours ago
  
  
  

  
  
  
  

 | 
show 4 more comments

<filesystem> (added in C++17) makes this very straightforward.

#include <cstdint>

#include <filesystem>



// ...



std::uintmax_t size = std::filesystem::file_size("c:foobar.txt");

share|improve this answer

answered 10 hours ago

HolyBlackCatHolyBlackCat

18.6k33 gold badges3737 silver badges7171 bronze badges

#include <cstdint>

#include <filesystem>



// ...



std::uintmax_t size = std::filesystem::file_size("c:foobar.txt");

share|improve this answer

answered 10 hours ago

HolyBlackCatHolyBlackCat

18.6k33 gold badges3737 silver badges7171 bronze badges

answered 10 hours ago

HolyBlackCatHolyBlackCat

18.6k33 gold badges3737 silver badges7171 bronze badges

answered 10 hours ago

HolyBlackCatHolyBlackCat

18.6k33 gold badges3737 silver badges7171 bronze badges

7

This might help.

#include <chrono>

#include <filesystem>  

#include <iostream>



namespace fs = std::filesystem;



int main(int argc, char* argv[])

{

    try

    {

        const auto fsize = fs::file_size("a.out");

        std::cout << fsize << 'n';

    }

    catch (const fs::filesystem_error& err)

    {

        std::cerr << "filesystem error! " << err.what() << 'n';

        if (!err.path1().empty())

            std::cerr << "path1: " << err.path1().string() << 'n';

        if (!err.path2().empty())

            std::cerr << "path2: " << err.path2().string() << 'n';

    }

    catch (const std::exception& ex)

    {

        std::cerr << "general exception: " << ex.what() << 'n';

    }



    // using error_code

    std::error_code ec{};

    auto size = std::filesystem::file_size("a.out", ec);

    if (ec == std::error_code{})

        std::cout << "size: " << size << 'n';

    else

        std::cout << "error when accessing test file, size is: " 

              << size << " message: " << ec.message() << 'n';

}

share|improve this answer

answered 10 hours ago

GOVIND DIXITGOVIND DIXIT

16511 silver badge1313 bronze badges

add a comment | 

7

This might help.

#include <chrono>

#include <filesystem>  

#include <iostream>



namespace fs = std::filesystem;



int main(int argc, char* argv[])

{

    try

    {

        const auto fsize = fs::file_size("a.out");

        std::cout << fsize << 'n';

    }

    catch (const fs::filesystem_error& err)

    {

        std::cerr << "filesystem error! " << err.what() << 'n';

        if (!err.path1().empty())

            std::cerr << "path1: " << err.path1().string() << 'n';

        if (!err.path2().empty())

            std::cerr << "path2: " << err.path2().string() << 'n';

    }

    catch (const std::exception& ex)

    {

        std::cerr << "general exception: " << ex.what() << 'n';

    }



    // using error_code

    std::error_code ec{};

    auto size = std::filesystem::file_size("a.out", ec);

    if (ec == std::error_code{})

        std::cout << "size: " << size << 'n';

    else

        std::cout << "error when accessing test file, size is: " 

              << size << " message: " << ec.message() << 'n';

}

share|improve this answer

answered 10 hours ago

GOVIND DIXITGOVIND DIXIT

16511 silver badge1313 bronze badges

add a comment | 

This might help.

#include <chrono>

#include <filesystem>  

#include <iostream>



namespace fs = std::filesystem;



int main(int argc, char* argv[])

{

    try

    {

        const auto fsize = fs::file_size("a.out");

        std::cout << fsize << 'n';

    }

    catch (const fs::filesystem_error& err)

    {

        std::cerr << "filesystem error! " << err.what() << 'n';

        if (!err.path1().empty())

            std::cerr << "path1: " << err.path1().string() << 'n';

        if (!err.path2().empty())

            std::cerr << "path2: " << err.path2().string() << 'n';

    }

    catch (const std::exception& ex)

    {

        std::cerr << "general exception: " << ex.what() << 'n';

    }



    // using error_code

    std::error_code ec{};

    auto size = std::filesystem::file_size("a.out", ec);

    if (ec == std::error_code{})

        std::cout << "size: " << size << 'n';

    else

        std::cout << "error when accessing test file, size is: " 

              << size << " message: " << ec.message() << 'n';

}

share|improve this answer

answered 10 hours ago

GOVIND DIXITGOVIND DIXIT

16511 silver badge1313 bronze badges

#include <chrono>

#include <filesystem>  

#include <iostream>



namespace fs = std::filesystem;



int main(int argc, char* argv[])

{

    try

    {

        const auto fsize = fs::file_size("a.out");

        std::cout << fsize << 'n';

    }

    catch (const fs::filesystem_error& err)

    {

        std::cerr << "filesystem error! " << err.what() << 'n';

        if (!err.path1().empty())

            std::cerr << "path1: " << err.path1().string() << 'n';

        if (!err.path2().empty())

            std::cerr << "path2: " << err.path2().string() << 'n';

    }

    catch (const std::exception& ex)

    {

        std::cerr << "general exception: " << ex.what() << 'n';

    }



    // using error_code

    std::error_code ec{};

    auto size = std::filesystem::file_size("a.out", ec);

    if (ec == std::error_code{})

        std::cout << "size: " << size << 'n';

    else

        std::cout << "error when accessing test file, size is: " 

              << size << " message: " << ec.message() << 'n';

}

share|improve this answer

answered 10 hours ago

GOVIND DIXITGOVIND DIXIT

16511 silver badge1313 bronze badges

answered 10 hours ago

GOVIND DIXITGOVIND DIXIT

16511 silver badge1313 bronze badges

answered 10 hours ago

GOVIND DIXITGOVIND DIXIT

16511 silver badge1313 bronze badges