About This Guide (GNAT User’s Guide for Native Platforms)

## 1 About This Guide ¶

This guide describes the use of GNAT, a compiler and software development toolset for the full Ada programming language. It documents the features of the compiler and tools, and explains how to use them to build Ada applications.

GNAT implements Ada 95, Ada 2005, Ada 2012, and Ada 2022. You may also invoke it in Ada 83 compatibility mode. By default, GNAT assumes Ada 2012, but you can use a compiler switch (Compiling Different Versions of Ada) to explicitly specify the language version. Throughout this manual, references to ‘Ada’ without a year suffix apply to all versions of the Ada language starting with Ada 95.

GNAT supports both the GCC and LLVM back end compilation families. Most GNAT versions use the GCC back end, but some are now available using the LLVM back end. In some places in this manual, we distinguish between the two back ends, but in most cases, everything in this manual applies to both back ends. We refer to GNAT with the LLVM back end as ‘GNAT LLVM’. See GNAT with the LLVM Back End for limitations of GNAT LLVM.