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Guidelines Support Library

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GSL: Guidelines Support Library

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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 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 [email protected] 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:


Supported? Description
owner an alias for a raw pointer
notnull 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
, however
enforces bounds checking. See the wiki for additional information.
spanp spans a range starting from a pointer to the first place for which the predicate is true
basiczstring A pointer to a C-string (zero-terminated array) with a templated char type
zstring An alias to `basiczstring

with a char type of char
czstring An alias tobasiczstring
with a char type of const char
wzstring An alias tobasiczstring
with a char type of wchar_t
cwzstring An alias tobasiczstring` with a char type of const wchart
u16zstring An alias to
with a char type of char16t
cu16zstring An alias to `basiczstring
with a char type of const char16_t
u32zstring An alias tobasiczstring` with a char type of char32t
cu32zstring An alias to
with a char type of const char32t
2. Owners
uniqueptr an alias to
sharedptr an alias to `std::sharedptr
stack_array a stack-allocated array
dyn_array a heap-allocated array
[3. Assertions][cg-assertions]
Expects a precondition assertion; on failure it terminates
Ensures a postcondition assertion; on failure it terminates
[4. Utilities][cg-utilities]
move_owner a helper function that moves oneowner
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 instantiatingfinalaction`
GSLSUPPRESS a macro that takes an argument and turns it into
[[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::ptrdifft)
joiningthread a RAII style version of
that joins
narrow a checked version of narrowcast; it can throw `narrowingerror
narrow_cast a narrowing cast for values and a synonym for static_cast
narrowing_error a custom exception type thrown bynarrow()`
5. Concepts

The following features do not exist in or have been removed from the C++ Core Guidelines:


Supported? Description
strictnotnull A stricter version of

with explicit constructors
multispan Deprecated. Multi-dimensional span.
stridedspan Deprecated. Support for this type has been discontinued.
basicstringspan Deprecated. Like
but for strings with a templated char type
stringspan Deprecated. An alias to basic</em>string<em>span with a char type of char
cstringspan Deprecated. An alias to
with a char type of const char
wstringspan Deprecated. An alias to basic</em>string<em>span with a char type of wchart
cwstringspan Deprecated. An alias to basic</em>string<em>span with a char type of const wchart
u16stringspan Deprecated. An alias to basic</em>string<em>span with a char type of char16t
cu16stringspan Deprecated. An alias to basic</em>string<em>span with a char type of const char16t
u32stringspan Deprecated. An alias to basic</em>string<em>span with a char type of char32t
cu32stringspan Deprecated. An alias to basic</em>string<em>span with a char type of const char32t

This is based on CppCoreGuidelines semi-specification.

Quick Start

Supported Compilers

The GSL officially supports the current and previous major release of MSVC, GCC, Clang, and XCode's Apple-Clang. See our latest test results for the most up-to-date list of supported configurations.


Toolset Versions Currently Tested
XCode 11.4 & 10.3
GCC 9 & 8
Clang 11 & 10
Visual Studio with MSVC VS2017 (15.9) & VS2019 (16.4)
Visual Studio with LLVM VS2017 (Clang 9) & VS2019 (Clang 10)

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!


CI/CD Status
Android CI_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

  1. 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
  2. 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
  3. Build the test suite (in this case, in the Debug configuration, Release is another good choice).

    cmake --build . --config Debug
  4. 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
cd vcpkg
./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 (

in the example above) or installation folder (after running the install). Eg.


/I c:\GSL\include



Include the library using:


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

which you can use via the usual


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)


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 "" GIT_TAG "v3.1.0" )


Now you can link against the GSL interface library


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 'GSLVSADDNATIVEVISUALIZERS'

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