# CMAKE_GENERATOR_TOOLSET

Native build system toolset specification provided by user.

Some CMake generators support a toolset specification to tell the native build system how to choose a compiler. If the user specifies a toolset (e.g. via the `cmake -T` option or via the `CMAKE_GENERATOR_TOOLSET` environment variable) the value will be available in this variable.

The value of this variable should never be modified by project code. A toolchain file specified by the `CMAKE_TOOLCHAIN_FILE` variable may initialize `CMAKE_GENERATOR_TOOLSET`. Once a given build tree has been initialized with a particular value for this variable, changing the value has undefined behavior.

Toolset specification is supported only on specific generators:

- Visual Studio Generators for VS 2010 and above

- The `Xcode` generator for Xcode 3.0 and above

- The `Green Hills MULTI` generator

See native build system documentation for allowed toolset names.

## Visual Studio Toolset Selection

The Visual Studio Generators support toolset specification using one of these forms:

- `toolset`

- `toolset[,key=value]*`

- `key=value[,key=value]*`

The `toolset` specifies the toolset name. The selected toolset name is provided in the `CMAKE_VS_PLATFORM_TOOLSET` variable.

The `key=value` pairs form a comma-separated list of options to specify generator-specific details of the toolset selection. Supported pairs are:

`cuda=<version>|<path>`

  Specify the CUDA toolkit version to use or the path to a standalone CUDA toolkit directory. Supported by VS 2010 and above. The version can only be used with the CUDA toolkit VS integration globally installed. See the `CMAKE_VS_PLATFORM_TOOLSET_CUDA` and `CMAKE_VS_PLATFORM_TOOLSET_CUDA_CUSTOM_DIR` variables.

`fortran=<compiler>`

  New in version 3.29.

  Specify the Fortran compiler to use, among those that have the required Visual Studio Integration feature installed. The value may be one of:

  `ifort`

    Intel classic Fortran compiler.

  `ifx`

    Intel oneAPI Fortran compiler.

  See the `CMAKE_VS_PLATFORM_TOOLSET_FORTRAN` variable.

`host=<arch>`

  Specify the host tools architecture as `x64` or `x86`. Supported by VS 2013 and above. See the `CMAKE_VS_PLATFORM_TOOLSET_HOST_ARCHITECTURE` variable.

`version=<version>`

  Specify the toolset version to use. Supported by VS 2017 and above with the specified toolset installed. See the `CMAKE_VS_PLATFORM_TOOLSET_VERSION` variable.

`VCTargetsPath=<path>`

  Specify an alternative `VCTargetsPath` value for Visual Studio project files. This allows use of VS platform extension configuration files (`.props` and `.targets`) that are not installed with VS.

## Visual Studio Toolset Customization

These are unstable interfaces with no compatibility guarantees because they hook into undocumented internal CMake implementation details. Institutions may use these to internally maintain support for non-public Visual Studio platforms and toolsets, but must accept responsibility to make updates as changes are made to CMake.

Additional `key=value` pairs are available:

`customFlagTableDir=<path>`

  New in version 3.21.

  Specify the absolute path to a directory from which to load custom flag tables stored as JSON documents with file names of the form `<platform>_<toolset>_<tool>.json` or `<platform>_<tool>.json`, where `<platform>` is the `CMAKE_VS_PLATFORM_NAME`, `<toolset>` is the `CMAKE_VS_PLATFORM_TOOLSET`, and `<tool>` is the tool for which the flag table is meant. This naming pattern is an internal CMake implementation detail. The `<tool>` names are undocumented. The format of the `.json` flag table files is undocumented.