.. _About_This_Guide: **************** About This Guide **************** .. only:: PRO For ease of exposition, 'GNAT Pro' will be referred to simply as 'GNAT' in the remainder of this document. This manual contains useful information in writing programs using the GNAT compiler. It includes information on implementation dependent characteristics of GNAT, including all the information required by Annex M of the Ada language standard. GNAT implements Ada 95, Ada 2005 and Ada 2012, and it may also be invoked in Ada 83 compatibility mode. By default, GNAT assumes Ada 2012, but you can override with a compiler switch to explicitly specify the language version. (Please refer to the *GNAT User's Guide* for details on these switches.) Throughout this manual, references to 'Ada' without a year suffix apply to all the Ada versions of the language. Ada is designed to be highly portable. In general, a program will have the same effect even when compiled by different compilers on different platforms. However, since Ada is designed to be used in a wide variety of applications, it also contains a number of system dependent features to be used in interfacing to the external world. .. index:: Implementation-dependent features .. index:: Portability Note: Any program that makes use of implementation-dependent features may be non-portable. You should follow good programming practice and isolate and clearly document any sections of your program that make use of these features in a non-portable manner. What This Reference Manual Contains =================================== This reference manual contains the following chapters: * :ref:`Implementation_Defined_Pragmas`, lists GNAT implementation-dependent pragmas, which can be used to extend and enhance the functionality of the compiler. * :ref:`Implementation_Defined_Attributes`, lists GNAT implementation-dependent attributes, which can be used to extend and enhance the functionality of the compiler. * :ref:`Standard_and_Implementation_Defined_Restrictions`, lists GNAT implementation-dependent restrictions, which can be used to extend and enhance the functionality of the compiler. * :ref:`Implementation_Advice`, provides information on generally desirable behavior which are not requirements that all compilers must follow since it cannot be provided on all systems, or which may be undesirable on some systems. * :ref:`Implementation_Defined_Characteristics`, provides a guide to minimizing implementation dependent features. * :ref:`Intrinsic_Subprograms`, describes the intrinsic subprograms implemented by GNAT, and how they can be imported into user application programs. * :ref:`Representation_Clauses_and_Pragmas`, describes in detail the way that GNAT represents data, and in particular the exact set of representation clauses and pragmas that is accepted. * :ref:`Standard_Library_Routines`, provides a listing of packages and a brief description of the functionality that is provided by Ada's extensive set of standard library routines as implemented by GNAT. * :ref:`The_Implementation_of_Standard_I/O`, details how the GNAT implementation of the input-output facilities. * :ref:`The_GNAT_Library`, is a catalog of packages that complement the Ada predefined library. * :ref:`Interfacing_to_Other_Languages`, describes how programs written in Ada using GNAT can be interfaced to other programming languages. * :ref:`Specialized_Needs_Annexes`, describes the GNAT implementation of all of the specialized needs annexes. * :ref:`Implementation_of_Specific_Ada_Features`, discusses issues related to GNAT's implementation of machine code insertions, tasking, and several other features. * :ref:`Implementation_of_Ada_2012_Features`, describes the status of the GNAT implementation of the Ada 2012 language standard. * :ref:`Security_Hardening_Features` documents GNAT extensions aimed at security hardening. * :ref:`Obsolescent_Features` documents implementation dependent features, including pragmas and attributes, which are considered obsolescent, since there are other preferred ways of achieving the same results. These obsolescent forms are retained for backwards compatibility. * :ref:`Compatibility_and_Porting_Guide` presents some guidelines for developing portable Ada code, describes the compatibility issues that may arise between GNAT and other Ada compilation systems (including those for Ada 83), and shows how GNAT can expedite porting applications developed in other Ada environments. * :ref:`gnu_fdl` contains the license for this document. .. index:: Ada 95 Language Reference Manual .. index:: Ada 2005 Language Reference Manual This reference manual assumes a basic familiarity with the Ada 95 language, as described in the :title:`International Standard ANSI/ISO/IEC-8652:1995`. It does not require knowledge of the new features introduced by Ada 2005 or Ada 2012. All three reference manuals are included in the GNAT documentation package. Conventions =========== .. index:: Conventions, typographical .. index:: Typographical conventions Following are examples of the typographical and graphic conventions used in this guide: * ``Functions``, ``utility program names``, ``standard names``, and ``classes``. * ``Option flags`` * :file:`File names` * ``Variables`` * *Emphasis* * [optional information or parameters] * Examples are described by text :: and then shown this way. * Commands that are entered by the user are shown as preceded by a prompt string comprising the ``$`` character followed by a space. Related Information =================== See the following documents for further information on GNAT: * :title:`GNAT User's Guide for Native Platforms`, which provides information on how to use the GNAT development environment. * :title:`Ada 95 Reference Manual`, the Ada 95 programming language standard. * :title:`Ada 95 Annotated Reference Manual`, which is an annotated version of the Ada 95 standard. The annotations describe detailed aspects of the design decision, and in particular contain useful sections on Ada 83 compatibility. * :title:`Ada 2005 Reference Manual`, the Ada 2005 programming language standard. * :title:`Ada 2005 Annotated Reference Manual`, which is an annotated version of the Ada 2005 standard. The annotations describe detailed aspects of the design decision. * :title:`Ada 2012 Reference Manual`, the Ada 2012 programming language standard. * :title:`DEC Ada, Technical Overview and Comparison on DIGITAL Platforms`, which contains specific information on compatibility between GNAT and DEC Ada 83 systems. * :title:`DEC Ada, Language Reference Manual`, part number AA-PYZAB-TK, which describes in detail the pragmas and attributes provided by the DEC Ada 83 compiler system.