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The original repository for fast_io has been archived due to git bloat over time, but older commits can still be found there.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

2. 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

3. 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

4. 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

5. 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