scnlib
scnlib
is a modern C++ library for scanning values. Think of it as a more C++-y scanf
, or the inverse of {fmt} / std::
.
The code lives over at GitHub, at https:/
#include <scn/scan.h> #include <print> // for std::print, C++23 int main() { auto result = scn::scan<int, double>("42, 3.14", "{}, {}"); if (result) { auto [first, second] = result->values(); std::println("first: {}, second: {}", first, second); // Prints "first: 42, second: 3.14\n" } }
About this documentation
This documentation is for the version 3.0 of the library. For version 2.0.3, see https:/
An introductory guide to the library can be found at Guide.
The API documentation is organized into modules, that can be found under Modules, behind the link at the top of the page. It can be searched directly using the search function in the navbar, or by pressing the TAB key. The most important modules are probably:
Installation
scnlib uses CMake for building. If you're already using CMake for your project, integration is easy with find_package
.
$ mkdir build
$ cd build
$ cmake ..
$ make -j
$ make install
# Find scnlib package find_package(scn CONFIG REQUIRED) # Target which you'd like to use scnlib add_executable(my_program ...) target_link_libraries(my_program scn::scn)
Another option would be usage through CMake's FetchContent
module.
FetchContent_Declare( scn GIT_REPOSITORY https://github.com/eliaskosunen/scnlib GIT_TAG v3.0.1 GIT_SHALLOW TRUE ) FetchContent_MakeAvailable(scn) # ... target_link_libraries(my_program scn::scn)
Dependencies
scnlib internally depends on fast_
By default, the CMake machinery automatically fetches, builds, and links it with FetchContent
. It's only used in the implementation, and it isn't visible to the users of the library.
Alternatively, by setting the CMake option SCN_USE_EXTERNAL_FAST_FLOAT
to ON
, fast_float is searched for using find_package
. Use this option if you already have the library installed.
To enable support for regular expressions, a regex engine backend is required. The default option is to use std::
, but an alternative can be picked by setting SCN_REGEX_BACKEND
to Boost
or re2
in CMake. These libraries are not downloaded with FetchContent
, but must be found externally.
The tests and benchmarks described below depend on GTest and Google Benchmark, respectively. These libraries are also fetched with FetchContent
, if necessary, controllable with SCN_USE_EXTERNAL_GTEST
and SCN_USE_EXTERNAL_BENCHMARK
, respectively.
Dependency | Version | Required | Information |
---|---|---|---|
fast_float | >= 5.0.0 | ✅ | Header only. Downloaded by default with |
Boost.Regex | N/A | ⚠️ | Required if |
re2 | >= 11.0.0 | ⚠️ | Required if SCN_REGEX_BACKEND is re2 .Must be available externally (not automatically downloaded). |
Tests and benchmarks
To build and run the tests and benchmarks for scnlib, clone the repository, and build it with CMake.
Building and running tests:
$ mkdir build $ cd build $ cmake -DCMAKE_BUILD_TYPE=Debug .. $ make -j $ ctest -j
Building and running the runtime performance benchmarks:
# create build directory like above $ cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INTERPROCEDURAL_OPTIMIZATION=ON -DSCN_NATIVE_ARCH=ON .. $ make -j # disable CPU frequency scaling $ sudo cpupower frequency-set --governor performance # run the benchmark of your choosing $ ./benchmark/runtime/integer/scn_int_bench # re-enable CPU frequency scaling $ sudo cpupower frequency-set --governor powersave
Without CMake
As mentioned above, the implementation of scnlib depends on fast_float. If you're not using CMake, you'll need to download it yourself, and make it available for the build. Since fast_float is a header-only library, it doesn't need to be built.
Headers for scnlib can be found from the include/
directory, and source files from the src/
directory.
Building and linking the library:
$ mkdir build
$ cd build
$ c++ -c -I../include/ ../src/*.cpp -Ipath-to-fast-float
$ ar rcs libscn.a *.o
libscn.a
can then be linked, as usual, with your project.
# in your project
$ c++ ... -Lpath-to-scn/build -lscn
Note, that scnlib requires at least C++17, so --std=c++17
(or equivalent, or newer) may need to be included in the build flags.
Configuration
There are numerous flags that can be used to configure the build of the library. All of them can be set through CMake at library build time, and some of them directly on the compiler command line, as indicated on the tables below.
Option | CMake | CLI | Default | Description |
---|---|---|---|---|
SCN_DISABLE_REGEX | ✅ | ✅ | OFF | Disable regular expression support |
SCN_REGEX_BACKEND | ✅ | ⚠️ | "std" | Regular expression backend to use<br>(use integer values on the command line) |
SCN_REGEX_BOOST_USE_ICU | ✅ | ✅ | OFF | Use the ICU when using the Boost regex backend |
SCN_DISABLE_IOSTREAM | ✅ | ✅ | OFF | Disable everything related to iostreams |
SCN_DISABLE_LOCALE | ✅ | ✅ | OFF | Disable everything related to C++ locales ( |
SCN_DISABLE_FROM_CHARS | ✅ | ✅ | OFF | Disable usage of (falling back on) |
SCN_DISABLE_STRTOD | ✅ | ✅ | OFF | Disable usage of (falling back on) |
SCN_DISABLE_(TYPE) | ✅ | ✅ | OFF | Disable support for a specific type |
Below, ENABLE_FULL
is true, if SCN_CI
is set in CMake, or scnlib is built as the primary project.
Option | CMake | CLI | Default | Description |
---|---|---|---|---|
SCN_USE_EXTERNAL_FAST_FLOAT | ✅ | ❌ | OFF | Use |
SCN_USE_EXTERNAL_GTEST | ✅ | ❌ | OFF | Use |
SCN_USE_EXTERNAL_BENCHMARK | ✅ | ❌ | OFF | Use |
SCN_TESTS | ✅ | ❌ | ENABLE_FULL | Enable building of tests |
SCN_DOCS | ✅ | ❌ | ENABLE_FULL | Enable building of documentation |
SCN_EXAMPLES | ✅ | ❌ | ENABLE_FULL | Enable building of examples |
SCN_INSTALL | ✅ | ❌ | ENABLE_FULL | Enable |
SCN_BENCHMARKS | ✅ | ❌ | ENABLE_FULL | Enable building of (runtime) benchmarks |
SCN_BENCHMARKS_BUILDTIME | ✅ | ❌ | ENABLE_FULL | Enable build-time benchmark targets |
SCN_BENCHMARKS_BINARYSIZE | ✅ | ❌ | ENABLE_FULL | Enable binary-size benchmark targets |
SCN_FUZZING | ✅ | ❌ | ENABLE_FULL | Enable building of fuzzer targets |
SCN_PEDANTIC | ✅ | ❌ | ENABLE_FULL | Enable pedantic compilation flags (mostly warnings) |
SCN_WERROR | ✅ | ❌ | SCN_CI | Enable warnings-as-errors |
SCN_COVERAGE | ✅ | ❌ | OFF | Enable code coverage reporting |
SCN_USE_NATIVE_ARCH | ✅ | ❌ | OFF | Add |
SCN_USE_HASWELL_ARCH | ✅ | ❌ | OFF | Add |
SCN_USE_ASAN , _UBSAN , _MSAN | ✅ | ❌ | OFF | Enable sanitizers |
License
The library is open source, licensed under the Apache License, version 2.0.
Copyright (c) 2017 Elias Kosunen
For further details, see the LICENSE file in the repository.