Environments

MSYS2 comes with different environments/subsystems and the first thing you have to decide is which one to use. The differences among the environments are mainly environment variables, default compilers/linkers, architecture, system libraries used etc. If you are unsure, go with MINGW64.

The MSYS environment contains the unix-like/cygwin based tools, lives under /usr and are special in that it is always active. All the other environments inherit from the MSYS environment and add various things on top of it.

For example, in the MINGW64 environment the $PATH variable starts with /mingw64/bin:/usr/bin so you get all mingw64 based tools as well as all msys tools.

Overview

	Name	Prefix	Toolchain	Architecture	C Library	C++ Library
	MSYS	/usr	gcc	x86_64	cygwin	libstdc++
	MINGW64	/mingw64	gcc	x86_64	msvcrt	libstdc++
	UCRT64	/ucrt64	gcc	x86_64	ucrt	libstdc++
	CLANG64	/clang64	llvm	x86_64	ucrt	libc++
	MINGW32	/mingw32	gcc	i686	msvcrt	libstdc++

GCC vs LLVM/Clang

These are the default compilers/toolchains used for building all packages in the respective repositories.

GCC based environments:

• Widely tested/used at this point
• Fortran support
• While there also exists a Clang package in the MINGW environments, that one still uses the GNU linker and the GNU C++ library. In some cases Clang is used to build packages as well there, in case upstream prefers Clang over GCC for example.

LLVM/Clang based environments:

• Only uses LLVM tools, LLD as a linker, LIBC++ as a C++ standard library
• Clang provides ASAN support
• Native support for TLS (Thread-local storage)
• LLD is faster than LD, but does not support all the features LD supports
• Some tools lack feature parity with equivalent GNU tools
• Supports ARM64/AArch64 architecture on Microsoft Windows 10

MSVCRT vs UCRT

These are two variants of the C standard library on Microsoft Windows.

MSVCRT (Microsoft Visual C++ Runtime) is available by default on all Microsoft Windows versions, but due to backwards compatibility issues is stuck in the past, not C99 compatible and is missing some features.

• It isn't C99 compatible, for example the printf() function family, but...
• mingw-w64 provides replacement functions to make things C99 compatible in many cases
• It doesn't support the UTF-8 locale
• Binaries linked with MSVCRT should not be mixed with UCRT ones because the internal structures and data types are different. Same rule is applied for MSVC compiled binaries because MSVC uses UCRT by default (if not changed).
• Works out of the box on every Microsoft Windows versions.

UCRT (Universal C Runtime) is a newer version which is also used by Microsoft Visual Studio by default. It should work and behave as if the code was compiled with MSVC.

• Better compatibility with MSVC, both at build time and at run time.
• It only ships by default on Windows 10 and for older versions you have to provide it yourself or depend on the user having it installed.