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fast_io

fast_io is a C++20 input/output library that provides exceptional speed and is designed to replace the commonly used <iostream> and <cstdio> libraries. It is a header-only library and is licensed under the MIT license, making it easy to include in any project. However, it requires a C++20 compiler that supports concepts.

The original repository for fast_io has been archived due to git bloat over time, but older commits can still be found there. old commits were here.

Examples

Print to stdout

#include <fast_io.h>

int main() {
	print("Hello, fast_io world!\n");
}

Memory map file

#include <fast_io.h>

int main() {
	fast_io::native_file_loader file_data("text.txt");
	// file_data satisfies std::ranges::contiguous_range
}

Other examples

For other up-to-date examples, please look in the examples/ folder.

Deprecated examples are here but they might not work anymore.

This i18n repo stores the i18n source files.

https://bitbucket.org/ejsvifq_mabmip/fast_io_i18n

F.A.Q.

What does "fast" mean in fast_io?

The term fast in fast_io does not necessarily imply that it is the fastest input/output library available (as it would have been named as fastest_io instead). Instead, the term refers to the fact that fast_io is notably faster than <iostream> and <cstdio> libraries in all cases.

What are the supported platforms, compilers...?

See support.md for a list of supported things and platform specific usage notes.

Other questions?

You can ask questions on the fast_io discord server or QQ group: 801441303.

Documentation

See either https://ewindy.gitee.io/fast_io_rst/index.html or https://gitee.com/qabeowjbtkwb/fast_io/wikis.

Features

  • As close to system call as possible.

  • Unicode support (UTF-8, UTF-16, UTF-32) + codecvt for GB18030 and UTF-EBCDIC (no libc correctly deals with it)

  • RAII for C FILE*, POSIX fd and win32/NT HANDLE

  • Interop with <cstdio> and <iostream>

  • No easily misused stuff like std::endl

  • Static I/O manipulators instead of format strings.

  • Optional locale.

  • Stateless I/O manipulation.

  • Consistent error handling; when available, exceptions as the only error reporting mechanism (no std::error_code, std::system_error or useless bounds checking)

  • Freestanding mode.

  • Address Sanitizer special code for protecting memory safety issues.

  • Dynamic Instrumentation Support

  • Supports POSIX iconv. You can use fast_io for your coding conversion.

  • Binary serialization for trivially copyable types and standard containers

  • Plays well with C++ containers (e.g. std::vector<fast_io::obuf_file> is valid)

  • Basic/Lua/Python/etc format (print, scan). No support for C and C++ since they are security hazards.

  • Provide APIs to expose the internal implementation of FILE* and C++ streams.

  • Native Handle Interface

  • Extremely easy to support custom devices

  • C and C++ style compile time open mode parsing.

  • No traits_type and EOF

  • Dynamic Type Support

  • Multi Process

  • Memory mapping

  • debugging IO (optionally with GUI)

  • Round-trip floating point algorithm

  • Hash algorithms support: intrinsic SHA-1, intrinsic HMAC-SHA1, intrinsic SHA-256, intrinsic HMAC-SHA256, SHA-512, HMAC-SHA512 as well as non crypto hash algorithms, such as Jenkins Hash.

  • zlib compression/decompression

  • Filesystem

  • OpenSSL BIO, Qt QFile, MFC CFile support

Post C++20

  1. Module support
  2. Coroutine support for async IO
  3. Improve and refactor code once Zero-overhead deterministic exceptions are added to the standard

Benchmarks

  1. I/O 10M integers

Goal: Print out ten million integers from 0 to 10M to file. Then reopen that file to scan back.

All benchmarks are in benchmarks/0000.10m_size_t/unit.

Notice: I modified libstdc++'s BUFSIZ 1048576 due to BUFSIZ is too small (512 bytes) for MinGW-W64, or it performs horribly.

Platform Windows MinGW-W64 GCC 11.0.0 MSVCRT + libstdc++
Method Output time Input time Comment
stdio.h(fprintf/fscanf) 2.412987s 5.607791s
fstream 0.462012s 1.192s
fstream with rdbuf.sputc trick 0.33895s 1.170173s
fast_io::i/obuf_file 0.04903s 0.080996s
fast_io::i/obuf_file_mutex 0.146064s 0.113155s thread safe
c_locale_i/obuf_file ("C") 0.065988s 0.086012s imbued with locale, locale "C"
c_locale_i/obuf_file local 0.153995s ❌ imbued with locale, locale ""
fmt::format_int+obuf_file 0.122999s ❌
fmt::format_int+ofstream 0.209055s ❌
fmt::format+ofstream 0.548s ❌ fmt makes things slower
fmt::print 0.663996s ❌ fmt makes things slower
std::to_chars+obuf_file 0.12s ❌
std::to_chars+ofstream 0.192s ❌
fast_io::c_file_unlocked 0.098999s 0.126003s I hacked MSVCRT's FILE* implementation
fast_io::c_file 0.298988s 0.318001s Thread Safe. I hacked MSVCRT's FILE* implementation
fast_io::filebuf_file 0.048999s 0.081s I hacked libstdc++'s streambuf/filebuf implementation
fast_io::iobuf_utf8_file_char16 0.124s 0.112001s UTF-16=>UTF-8 with SSE
fast_io::iobuf_utf8_file_char32 0.110999s 0.111011s UTF-32=>UTF-8 with SSE
std::wofstream 2.64s 3.843735s wofstream with std::locale codecvt. Extremely slow tbh.
fast_io::wfilebuf_io_observer 2.415692s 2.497704s wofstream with std::locale codecvt. This proves fstream can never get fixed.
Rust language 0.483s ❌ RUST IS SLOW. Also Rust does not deal with locale. Think how bad it is.
Rust itoa library 0.4.6 > 0.165s ❌ I ignored the \n part for it to ensure no bias.

Rust language is 10x slower than fast_io. + binary bloat and itoa library is still extremely slow and usable for me. It is at least 3x slower than fast_io.

Run the same test on MSVC 19.26.28805.

Platform Windows MSVC 19.26.28805 Install fmtlib wastes time of my life
Method Output time Input time Comment
stdio.h(fprintf/fscanf) 1.5353597s 1.4157233s
fstream 3.6350262s 3.8420339s
fstream with rdbuf.sputc trick 3.3735902s 3.8145566s
fast_io::i/obuf_file 0.0631433s 0.1030554s
fast_io::i/obuf_file_mutex 0.2190659s 0.2485886s thread safe
std::to_chars+obuf_file 0.1641641s ❌
std::to_chars+ofstream 0.5461922s ❌
fast_io::c_file_unlocked 0.1102575s 0.2399757s I hacked Universal CRT's FILE* implementation
fast_io::c_file 0.2034755s 0.2621148s Thread Safe. I hacked UCRT's FILE* implementation
fast_io::filebuf_file 0.126661s 0.2378803s I hacked MSVC STL's streambuf/filebuf implementation

Run the same test on GCC 11. glibc + libstdc++

Platform Linux GCC 11.0.0 glibc + libstdc++
Method Output time Input time Comment
stdio.h(fprintf/fscanf) 0.532792935s 0.591907111s
fstream with rdbuf.sputc trick 0.318896068s 0.429406415s
fast_io::i/obuf_file 0.050300857s 0.065372395s
fast_io::i/obuf_file_mutex 0.05290654s 0.083040518s thread safe
c_locale_i/obuf_file ("C") 0.051939052s 0.065820056s imbued with locale, locale "C"
c_locale_i/obuf_file local 0.162406082s ❌ imbued with locale, locale ""
std::to_chars+obuf_file 0.115453587s ❌
fmt::format_int+obuf_file 0.1183587s ❌
fmt::format_int+ofstream 0.195914384s ❌
fmt::format+ofstream 0.633590975s ❌ fmt makes things slower
fmt::print 0.495270371s ❌ fmt makes things slower
boost::iostreams 0.400906063s 0.444717051s Using boost iostreams does not make your code faster
fast_io::c_file_unlocked 0.060076723s 0.073299716s I hacked glibc's FILE* implementation
fast_io::c_file 0.092490191s 0.104545535s Thread Safe. I hacked glibc's FILE* implementation
fast_io::filebuf_file 0.052251608s 0.06655806s I hacked libstdc++'s streambuf/filebuf implementation

You can see fast_io can also boost the performance of existing facilities for 10x! Yes, it can even improve FILE* and fstream's performance for 10x depending on platforms since I use concepts to abstract them all. fmtlib actually slows down I/O performance.

  1. Output 10M double in round-trip mode with Ryu algorithm

We only perform this test for MSVC since only msvc's charconv implements it. Yes. fast_io defeats msvc's charconv for over 20% for running the same algorithm.

All benchmarks are in benchmarks/0001.10m_double/charconv.

Run the same test on MSVC 19.26.28805.

Platform Windows MSVC 19.26.28805
Method Output time Comment
i/obuf_file 0.4653818s
charconv + obuf_file 0.6011s
  1. Raw I/O Performance

All benchmarks are in benchmarks/0014.file_io/file_io.

Output 100000000x "Hello World\n"

Notice: I modified libstdc++'s std::filebuf's BUFSIZ to 1048576 due to BUFSIZ is too small (512 bytes) for MinGW-W64 or it performs horribly.

Platform Windows MinGW-W64 GCC 11.0.0 MSVCRT + libstdc++
Method Output time Comment
fwrite 2.524001s
fstream 1.013001s
fast_io::obuf_file 0.437998s
fast_io::obuf_file_mutex 1.371s Thread safe
fast_io::c_file_unlocked 1.164997s I hacked MSVCRT's FILE* implementation
fast_io::c_file 3.337945s Thread Safe. I hacked MSVCRT's FILE* implementation. Need further optimization
fast_io::filebuf_file 0.467001s I hacked libstdc++'s std::filebuf implementation
Platform Linux GCC 11.0.0 glibc + libstdc++
Method Output time Comment
fwrite 1.457288317s
fstream 1.249783346s
fast_io::obuf_file 0.494827134s
fast_io::obuf_file_mutex 0.497138826s Thread safe
fast_io::c_file_unlocked 0.687976666s I hacked glibc's FILE* implementation
fast_io::c_file 0.910792697s Thread Safe. I hacked glibc's FILE* implementation
fast_io::filebuf_file 0.526955039s I hacked libstdc++'s std::filebuf implementation
Platform Windows MSVC 19.26.28805 UCRT + MSVC STL
Method Output time Comment
fwrite 3.3139122s
fstream 1.7184119s
fast_io::obuf_file 0.7996034s
fast_io::obuf_file_mutex 2.2949221s Thread safe. It looks like std::mutex is horribly slow for MSVC STL.
fast_io::c_file_unlocked 1.2103924s I hacked UCRT's FILE* implementation
fast_io::c_file 2.3604295s Thread Safe. I hacked UCRT's FILE* implementation
fast_io::filebuf_file 1.2805368s I hacked MSVC STL's std::filebuf implementation
  1. Binary Size Just use the benchmark in benchmarks/0014.file_io/file_io. Dude, you should avoid stream as plague tbh. It is not healthy.
Platform Windows MinGW-W64 GCC 11.0.0 MSVCRT + libstdc++ + static compile
Method Binary Size Comment
fstream 925KB Use fstream is not good for your health since std::locale bloats your binary.
fast_io::obuf_file 155KB
fast_io::c_file_unlocked 157KB I hacked MSVCRT's FILE* implementation
fast_io::c_file 157KB Thread Safe. I hacked MSVCRT's FILE* implementation
fast_io::filebuf_file 933KB I hacked libstdc++'s std::filebuf implementation. C++ stream sucks
  1. Code Convert

Generate 100000000 🚄 emojis by using the program in benchmarks/0020.utf/fill_nc.cc

Benchmarks are in examples/0043.iconv Universal iconv. (UTF-8 to GB18030 as an example) iconv test:

Platform Windows MinGW-W64 GCC 11.0.0 MSVCRT + libstdc++
Method Elapsed time Comment
iconv command 1.529s
universal.cc 1.293s use POSIX libiconv

UTF8->UTF16LE

Benchmarks are in examples/0022.utf

iconv test:

Platform Windows MinGW-W64 GCC 11.0.0 MSVCRT + libstdc++
Method Elapsed time Comment
iconv command 0.967s GNU iconv. No BOM which sucks
utf8_file_to_utf16_file.cc 0.498s I use the SSE algorithms provided by the utf-utils project.

UTF8->UTF32LE

Benchmarks are in examples/0022.utf

iconv test:

Platform Windows MinGW-W64 GCC 11.0.0 MSVCRT + libstdc++
Method Elapsed time Comment
iconv command 0.844s GNU iconv. No BOM which sucks
utf8_file_to_utf32_file.cc 0.442s I use the SSE algorithms provided by the utf-utils project.

Credits

The creation and development of this project were made possible thanks to the valuable contributions of various open-source projects. While the code was not copied directly from these projects, I used them as references and re-implemented them to suit the specific purposes of this library. In some cases, integration issues arose that required modifications to the original code. I am grateful to these projects and their developers for their commitment to making their code open and accessible to the wider community.

Project Url
Grisu-Exact https://github.com/jk-jeon/Grisu-Exact
Ryu https://github.com/ulfjack/ryu
SHA-Intrinsics https://github.com/noloader/SHA-Intrinsics
SHA1 https://github.com/vog/sha1
UTF-utils https://github.com/BobSteagall/utf_utils
jenkins-hash-java https://github.com/vkandy/jenkins-hash-java
md5 https://github.com/JieweiWei/md5
ReactOS https://github.com/reactos/reactos
dirent_h https://github.com/win32ports/dirent_h
GNU C library https://www.gnu.org/software/libc/
GNU Newlib https://sourceware.org/newlib/
Dragonbox https://github.com/jk-jeon/dragonbox
JEAIII https://github.com/jeaiii/itoa
Crypto++ https://github.com/weidai11/cryptopp
MyItoA https://gitee.com/xjkp2283572185/MyStd

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Freestanding fast input/output for C++20

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