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GSL: Guidelines Support Library
The Guidelines Support Library (GSL) contains functions and types that are suggested for use by the C++ Core Guidelines maintained by the Standard C++ Foundation. This repo contains Microsoft's implementation of GSL.
The entire implementation is provided inline in the headers under the gsl directory. The implementation generally assumes a platform that implements C++14 support.
While some types have been broken out into their own headers (e.g. gsl/span), it is simplest to just include gsl/gsl and gain access to the entire library.
NOTE: We encourage contributions that improve or refine any of the types in this library as well as ports to other platforms. Please see CONTRIBUTING.md for more information about contributing.
Project Code of Conduct
This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.
Usage of Third Party Libraries
This project makes use of the Google Test testing library. Please see the ThirdPartyNotices.txt file for details regarding the licensing of Google Test.
Supported features
Microsoft GSL implements the following from the C++ Core Guidelines:
| Feature | Supported? | Description |
|---|---|---|
| 1. Views | ||
| owner | ☑ | an alias for a raw pointer |
| not_null | ☑ | restricts a pointer / smart pointer to hold non-null values |
| span | ☑ | a view over a contiguous sequence of memory. Based on the standardized verison of std::span, however gsl::span enforces bounds checking. See the wiki for additional information. |
| span_p | ☐ | spans a range starting from a pointer to the first place for which the predicate is true |
| basic_zstring | ☑ | A pointer to a C-string (zero-terminated array) with a templated char type |
| zstring | ☑ | An alias to basic_zstring with dynamic extent and a char type of char |
| czstring | ☑ | An alias to basic_zstring with dynamic extent and a char type of const char |
| wzstring | ☑ | An alias to basic_zstring with dynamic extent and a char type of wchar_t |
| cwzstring | ☑ | An alias to basic_zstring with dynamic extent and a char type of const wchar_t |
| u16zstring | ☑ | An alias to basic_zstring with dynamic extent and a char type of char16_t |
| cu16zstring | ☑ | An alias to basic_zstring with dynamic extent and a char type of const char16_t |
| u32zstring | ☑ | An alias to basic_zstring with dynamic extent and a char type of char32_t |
| cu32zstring | ☑ | An alias to basic_zstring with dynamic extent and a char type of const char32_t |
| 2. Owners | ||
| unique_ptr | ☑ | an alias to std::unique_ptr |
| shared_ptr | ☑ | an alias to std::shared_ptr |
| stack_array | ☐ | a stack-allocated array |
| dyn_array | ☐ | a heap-allocated array |
| 3. Assertions | ||
| Expects | ☑ | a precondition assertion; on failure it terminates |
| Ensures | ☑ | a postcondition assertion; on failure it terminates |
| 4. Utilities | ||
| move_owner | ☐ | a helper function that moves one owner to the other |
| byte | ☑ | either an alias to std::byte or a byte type |
| final_action | ☑ | a RAII style class that invokes a functor on its destruction |
| finally | ☑ | a helper function instantiating final_action |
| GSL_SUPPRESS | ☑ | a macro that takes an argument and turns it into [[gsl::suppress(x)]] or [[gsl::suppress("x")]] |
| implicit | ☐ | a "marker" to put on single-argument constructors to explicitly make them non-explicit |
| index | ☑ | a type to use for all container and array indexing (currently an alias for std::ptrdiff_t) |
| joining_thread | ☐ | a RAII style version of std::thread that joins |
| narrow | ☑ | a checked version of narrow_cast; it can throw narrowing_error |
| narrow_cast | ☑ | a narrowing cast for values and a synonym for static_cast |
| narrowing_error | ☑ | a custom exception type thrown by narrow() |
| 5. Concepts | ☐ |
The following features do not exist in or have been removed from the C++ Core Guidelines:
| Feature | Supported? | Description |
|---|---|---|
| strict_not_null | ☑ | A stricter version of not_null with explicit constructors |
| multi_span | ☐ | Deprecated. Multi-dimensional span. |
| strided_span | ☐ | Deprecated. Support for this type has been discontinued. |
| basic_string_span | ☐ | Deprecated. Like span but for strings with a templated char type |
| string_span | ☐ | Deprecated. An alias to basic_string_span with a char type of char |
| cstring_span | ☐ | Deprecated. An alias to basic_string_span with a char type of const char |
| wstring_span | ☐ | Deprecated. An alias to basic_string_span with a char type of wchar_t |
| cwstring_span | ☐ | Deprecated. An alias to basic_string_span with a char type of const wchar_t |
| u16string_span | ☐ | Deprecated. An alias to basic_string_span with a char type of char16_t |
| cu16string_span | ☐ | Deprecated. An alias to basic_string_span with a char type of const char16_t |
| u32string_span | ☐ | Deprecated. An alias to basic_string_span with a char type of char32_t |
| cu32string_span | ☐ | Deprecated. An alias to basic_string_span with a char type of const char32_t |
This is based on CppCoreGuidelines semi-specification.
Quick Start
Supported Compilers
The GSL officially supports the following versions of MSVC, GCC, Clang, and XCode's Apple-Clang.
| Compiler | Toolset Versions Currently Tested |
|---|---|
| XCode | 12.4 & 11.3 |
| GCC | 9.3.0 & 7.5.0 |
| Clang | 11.0.0 & 9.0.0 |
| Visual Studio with MSVC | VS2017 (15.9.21) & VS2019 (16.11.2) |
If you successfully port GSL to another platform, we would love to hear from you!
- Submit an issue specifying the platform and target.
- Consider contributing your changes by filing a pull request with any necessary changes.
- If at all possible, add a CI/CD step and add the button to the table below!
| Target | CI/CD Status |
|---|---|
| iOS |  |
| Android |  |
Note: These CI/CD steps are run with each pull request, however failures in them are non-blocking.
Building the tests
To build the tests, you will require the following:
- CMake, version 3.1.3 (3.2.3 for AppleClang) or later to be installed and in your PATH.
These steps assume the source code of this repository has been cloned into a directory named c:\GSL.
-
Create a directory to contain the build outputs for a particular architecture (we name it c:\GSL\build-x86 in this example).
cd GSL md build-x86 cd build-x86 -
Configure CMake to use the compiler of your choice (you can see a list by running
cmake --help).cmake -G "Visual Studio 15 2017" c:\GSL -
Build the test suite (in this case, in the Debug configuration, Release is another good choice).
cmake --build . --config Debug -
Run the test suite.
ctest -C Debug
All tests should pass - indicating your platform is fully supported and you are ready to use the GSL types!
Building GSL - Using vcpkg
You can download and install GSL using the vcpkg dependency manager:
git clone https://github.com/Microsoft/vcpkg.git
cd vcpkg
./bootstrap-vcpkg.sh
./vcpkg integrate install
vcpkg install ms-gsl
The GSL port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please create an issue or pull request on the vcpkg repository.
Using the libraries
As the types are entirely implemented inline in headers, there are no linking requirements.
You can copy the gsl directory into your source tree so it is available to your compiler, then include the appropriate headers in your program.
Alternatively set your compiler's include path flag to point to the GSL development folder (c:\GSL\include in the example above) or installation folder (after running the install). Eg.
MSVC++
/I c:\GSL\include
GCC/clang
-I$HOME/dev/GSL/include
Include the library using:
#include <gsl/gsl>
Usage in CMake
The library provides a Config file for CMake, once installed it can be found via
find_package(Microsoft.GSL CONFIG)
Which, when successful, will add library target called Microsoft.GSL::GSL which you can use via the usual
target_link_libraries mechanism.
FetchContent
If you are using cmake version 3.11+ you can use the offical FetchContent module. This allows you to easily incorporate GSL into your project.
# NOTE: This example uses cmake version 3.14 (FetchContent_MakeAvailable).
# Since it streamlines the FetchContent process
cmake_minimum_required(VERSION 3.14)
include(FetchContent)
# In this example we are picking a specific tag.
# You can also pick a specific commit, if you need to.
FetchContent_Declare(GSL
GIT_REPOSITORY "https://github.com/microsoft/GSL"
GIT_TAG "v3.1.0"
)
FetchContent_MakeAvailable(GSL)
# Now you can link against the GSL interface library
add_executable(foobar)
# Link against the interface library (IE header only library)
target_link_libraries(foobar PRIVATE GSL)
Debugging visualization support
For Visual Studio users, the file GSL.natvis in the root directory of the repository can be added to your project if you would like more helpful visualization of GSL types in the Visual Studio debugger than would be offered by default.
If you are using cmake this will be done automatically for you. See 'GSL_VS_ADD_NATIVE_VISUALIZERS'