Fortran 90 Language Guide

PREFACE The FORTRAN programming language was designed in the 1950s and standardized in 1966. That version of the language was later called FORTRAN 66. FORTRAN 66 quickly developed into the most important programming language for the development of engineering and scientific applications. In 1978, the language was redesigned and standardized again and called FORTRAN 77. However, this FORTRAN version was not yet a modern language as far as software engineering and programming methodology were concerned. In 1991, a new version of the language was standardized. Its name is Fortran 90. This version is a powerful tool, in fact it is closer to the state of the art of high level problem oriented programming languages than other famous languages that are used for the same area of application. The next revision of the language is planned for 1995; it will be a minor revision of Fortran 90. The next major language revision is planned for the year 2000. This "Fortran90 Language Guide" is a comprehensible description of the com­ plete Fortran 90 programming language as it is defined in the standard docu­ ment [1]. It is already in accordance with the two corrigenda [2] [3] of the standard document. The standard document is a reference book for compiler writers and those experts who already know all about Fortran 90, but it is use­ less for beginners and rather impractical even for experienced programmers.

1 Source form.- 1.1 Fixed Source Form.- 1.2 Free Source Form.- 1.3 Embedding of Program Lines by INCLUDE.- 1.4 Classification of Fortran Statements.- 1.5 Statement Ordering.- 2 Type Concept.- 2.1 Intrinsic Types.- 2.1.1 Integer Type.- 2.1.2 Real Type and Double Precision Real Type.- 2.1.3 Complex Type.- 2.1.4 Logical Type.- 2.1.5 Character Type.- 2.2 Derived Types.- 2.2.1 Derived Type Definition.- 2.2.2 Type Component Definition.- 2.2.3 Private and Public Derived Type Definitions.- 2.2.4 Structure Objects.- 3 Lexical Tokens.- 3.1 Scoping Units.- 3.2 Keywords.- 3.3 Names.- 3.4 Operators.- 3.5 Statement Labels.- 3.6 Literal Constants.- 3.6.1 Integer Literal Constants.- 3.6.2 Real Literal Constants.- 3.6.3 Double Precision Real Literal Constants.- 3.6.4 Complex Literal Constants.- 3.6.5 Logical Literal Constants.- 3.6.6 Character Literal Constants.- 3.6.7 Binary, Octal, and Hexadecimal Literal Constants.- 4 Data Objects.- 4.1 Constants.- 4.2 Variables.- 4.3 Sealars.- 4.3.1 Character Substrings.- 4.4 Arrays.- 4.4.1 Inner Structure of Arrays.- 4.5 Structure Components.- 4.6 Automatic Variables.- 4.7 Association.- 4.7.1 Name Association.- 4.7.2 Pointer Association.- 4.7.3 Storage Association.- 4.8 Definition Status.- 5 Pointers.- 5.1 Pointer Processing.- 5.1.1 Creation of Pointer Targets.- 5.1.2 Association Status.- 5.1.3 Deallocation of Pointer Targets.- 5.1.4 Nullification of Pointer Associations.- 6 Array Processing.- 6.1 Array Declaration.- 6.1.1 Explicit-Shape Arrays.- 6.1.2 Assumed-Shape Arrays.- 6.1.3 Assumed-Size Arrays.- 6.2 Reference and Use.- 6.2.1 Whole Arrays.- 6.2.2 Array Elements.- 6.2.3 Array Sections.- 6.2.3.1 Subscript-Triplet.- 6.2.3.2 Vector-Subscript.- 6.2.3.3 Array Sections of Substrings.- 6.3 Memory Management and Dynamic Control.- 6.3.1 Automatic Arrays.- 6.3.2 Allocatable Arrays.- 6.3.3 Array Pointers.- 6.4 Construction of Array Values.- 6.5 Operations on Arrays.- 6.5.1 Array Expressions.- 6.5.2 Array Subprograms.- 6.5.3 Array Assignments.- 7 Expressions.- 7.1 Numeric Intrinsic Expressions.- 7.2 Relational Intrinsic Expressions.- 7.2.1 Numeric Relational Intrinsic Expressions.- 7.2.2 Character Relational Intrinsic Expressions.- 7.3 Logical Intrinsic Expressions.- 7.4 Character Intrinsic Expressions.- 7.5 Defined Expressions.- 7.5.1 Defined Operators and Extended Intrinsic Operators.- 7.5.1.1 Nonextended Defined Operator.- 7.5.1.2 Extended Defined Operator.- 7.5.1.3 Extended Intrinsic Operator.- 7.6 Common Rules for Expressions.- 7.6.1 Precedence of Operators.- 7.6.2 Interpretation of Expressions.- 7.6.3 Evaluation of Expressions.- 7.7 Special Expressions.- 7.7.1 Constant Expressions.- 7.7.2 Initialization Expressions.- 7.7.3 Specification Expressions.- 8 Assignments.- 8.1 ASSIGN Statement.- 8.2 Intrinsic Assignment Statements.- 8.2.1 Numeric Assignment Statement.- 8.2.2 Logical Assignment Statement.- 8.2.3 Character Assignment Statement.- 8.2.4 Assignment Statement for Derived Types.- 8.3 Defined Assignment Statements.- 8.3.1 Nonextended Defined Assignment.- 8.3.2 Extended Defined Assignment.- 8.4 Masked Array Assignments.- 8.4.1 WHERE Statement.- 8.4.2 WHERE Construct Statement, ELSEWHERE Statement, and END WHERE Statement.- 8.4.2.1 WHERE Constructs.- 8.4.3 Common Rules for Masked Array Assignments.- 8.5 Pointer Assignment Statement.- 9 Declarations and Specifications.- 9.1 Attributes.- 9.1.1 ALLOCATABLE Attribute.- 9.1.2 DATA Attribute.- 9.1.3 DIMENSION Attribute.- 9.1.4 EXTERNAL Attribute.- 9.1.5 INTENT Attribute.- 9.1.6 INTRINSIC Attribute.- 9.1.7 OPTIONAL Attribute.- 9.1.8 PARAMETER Attribute.- 9.1.9 POINTER Attribute.- 9.1.10 PRIVATE Attribute.- 9.1.11 PUBLIC Attribute.- 9.1.12 SAVE Attribute.- 9.1.13 TARGET Attribute.- 9.2 Type Declaration Statements.- 9.2.1 INTEGER Statement.- 9.2.2 REAL Statement.- 9.2.3 DOUBLE PRECISION Statement.- 9.2.4 COMPLEX Statement.- 9.2.5 LOGICAL Statement.- 9.2.6 CHARACTER Statement.- 9.2.6.1 Character Length.- 9.2.7 TYPE Declaration Statement.- 9.3 Attribute Specification Statements.- 9.3.1 ALLOCATABLE Statement.- 9.3.2 DATA Statement.- 9.3.2.1 Implied-DO.- 9.3.3 DIMENSION Statement.- 9.3.4 EXTERNAL Statement.- 9.3.5 INTENT Statement.- 9.3.6 INTRINSIC Statement.- 9.3.7 OPTIONAL Statement.- 9.3.8 PARAMETER Statement.- 9.3.9 POINTER Statement.- 9.3.10 PRIVATE Statement.- 9.3.11 PUBLIC Statement.- 9.3.12 SAVE Statement.- 9.3.13 TARGET Statement.- 9.4 Additional Specification Statements.- 9.4.1 COMMON Statement.- 9.4.2 EQUIVALENCE Statement.- 9.4.2.1 EQUIVALENCE and COMMON.- 9.4.3 IMPLICIT Statement.- 9.4.4 NAMELIST Statement.- 10 Execution Control.- 10.1 GOTO Statements.- 10.1.1 Unconditional GOTO Statement.- 10.1.2 Computed GOTO Statement.- 10.1.3 Assigned GO TO Statement.- 10.2 IF Statements.- 10.2.1 Arithmetic IF Statement.- 10.2.2 Logical IF Statement.- 10.3 IF Construct.- 10.3.1 Simple IF Constructs.- 10.3.2 Nested IF Constructs.- 10.4 CASE Construct.- 10.4.1 Simple CASE Constructs.- 10.5 DO Construct.- 10.5.1 DO Statement.- 10.5.2 Do-Termination Statement.- 10.5.3 Forms for DO Constructs.- 10.5.4 Execution of a DO Construct.- 10.5.4.1 Additional Details about Count Loops.- 10.5.4.2 Additional Details about WHILE Loops.- 10.5.4.3 Additional Details about Endless Loops.- 10.5.4.4 CYCLE Statement, EXIT Statement.- 10.5.5 Nested DO Constructs.- 10.6 Nested Constructs.- 10.7 CONTINUE Statement.- 10.8 PAUSE Statement.- 10.9 STOP Statement.- 10.10 CALL, END, and RETURN Statements.- 11 Input/Output.- 11.1 Records.- 11.2 Files.- 11.3 File Attribute of External Files.- 11.3.1 File Names.- 11.3.2 Access Methods.- 11.3.2.1 Sequential Access.- 11.3.2.2 Direct Access.- 11.3.3 Form of a File.- 11.3.4 File Position.- 11.4 Units.- 11.5 Preconnected Units and Predefined Files.- 11.6 Input/Output Statements.- 11.6.1 Input /Output Specifiers.- 11.6.1.1 UNIT= Specifier.- 11.6.1.2 FMT= Specifier.- 11.6.1.3 NML= Specifier.- 11.6.1.4 REC= Specifier.- 11.6.1.5 ADVANCE= Specifier.- 11.6.1.6 End-of-Record Condition and EOR= Specifier.- 11.6.1.7 IOSTAT= Specifier.- 11.6.1.8 Error Conditions and ERR= Specifier.- 11.6.1.9 End-of-File Condition and END= Specifier.- 11.6.1.10 SIZE= Specifier.- 11.6.2 Input/Output Lists.- 11.6.2.1 Implied-DO.- 11.6.3 Data Transfer Statements.- 11.6.3.1 Formatted Input/Output.- 11.6.3.2 Unformatted Input/Output.- 11.6.3.3 List-Directed Input/Output.- 11.6.3.4 Internal Input/Output.- 11.6.3.5 Namelist Input/output.- 11.6.3.6 Nonadvancing Input/Output.- 11.6.3.7 Printing.- 11.6.4 File Status Statements.- 11.6.4.1 OPEN Statement.- 11.6.4.2 CLOSE Statement.- 11.6.4.3 INQUIRE Statement.- 11.6.5 File Positioning Statements.- 12 Formats.- 12.1 Format Specification.- 12.1.1 Format Specification in FORMAT Statement.- 12.1.2 Character Format Specification.- 12.2 Interaction between Input/Output List and Format.- 12.2.1 Repeat Specification, Groups of Edit Descriptors.- 12.2.2 Format Reversion.- 12.3 Edit Descriptors.- 12.3.1 A Edit Descriptors.- 12.3.2 B Edit Descriptors.- 12.3.3 Blank Control Edit Descriptors.- 12.3.4 Character Constant Edit Descriptors.- 12.3.5 Colon Edit Descriptor.- 12.3.6 D Edit Descriptor.- 12.3.7 E Edit Descriptors.- 12.3.8 EN Edit Descriptors.- 12.3.9 ES Edit Descriptors.- 12.3.10 F Edit Descriptor.- 12.3.11 G Edit Descriptors.- 12.3.12 H Edit Descriptor.- 12.3.13 I Edit Descriptors.- 12.3.14 L Edit Descriptor.- 12.3.15 O Edit Descriptors.- 12.3.16 P Edit Descriptor, Scale Factor.- 12.3.17 Sign Control Edit Descriptors.- 12.3.18 Slash Edit Descriptor.- 12.3.19 Tabulator Edit Descriptors.- 12.3.20 X Edit Descriptor.- 12.3.21 Z Edit Descriptors.- 13 Program Units and Subprograms.- 13.1 Main Program.- 13.2 Modules.- 13.2.1 USE Statement.- 13.3 Block Data Program Units.- 13.4 Subprograms.- 13.4.1 User-Defined Functions (except Statement Functions).- 13.4.1.1 Function Definition.- 13.4.1.2 Explicit Invocation of a Function, Function Reference.- 13.4.1.3 Operator Functions.- 13.4.2 User-Defined Subroutines.- 13.4.2.1 Subroutine Definition.- 13.4.2.2 Explicit Invocation of a Subroutine, CALL Statement.- 13.4.2.3 Assignment Subroutines.- 13.4.3 External Subprograms.- 13.4.4 Internal Subprograms.- 13.4.5 Module Subprograms.- 13.4.6 Dummy Subprograms.- 13.4.7 Statement Functions.- 13.4.7.1 Statement Function Definition.- 13.4.7.2 Invocation of a Statement Function.- 13.4.8 Interface Blocks.- 13.4.9 Overloaded Generic Subprogram Names.- 13.4.10 Additional Entry Points, ENTRY Statement.- 13.4.11 Return from the Invoked Subprogram.- 13.5 Communication between Program Units and Subprograms.- 13.5.1 Argument Lists.- 13.5.1.1 Dummy Argument List.- 13.5.1.2 Actual Argument List.- 13.5.2 Argument Association.- 13.5.2.1 Data Objects as Dummy Arguments.- 13.5.2.2 Implicit Association of Two Dummy Arguments.- 13.5.2.3 Length of Character Dummy Arguments.- 13.5.2.4 Scalar Arguments.- 13.5.2.5 Dummy (Argument) Arrays.- 13.5.2.6 Dummy (Argument) Pointers.- 13.5.2.7 Sequence Association.- 13.5.2.8 Assumed-Size Arrays.- 13.5.2.9 Assumed-Shape Arrays.- 13.5.2.10 Restrictions on the Association of Data Entities.- 13.5.2.11 Dummy Subprograms.- 13.5.2.12 Asterisk Dummy Arguments.- 13.5.3 Optional Dummy Arguments.- 13.5.4 Dummy Argument with INTENT Attribute.- 13.5.5 Common Blocks.- 14 Intrinsic Subprograms.- 14.1 Intrinsic Functions.- 14.1.1 Table of Intrinsic Functions.- 14.2 Intrinsic Subroutines.- 14.3 Intrinsic Subprogram Reference.- 14.4 Intrinsic Subprogram Definitions.- 14.4.1 Descriptions.- A Character sets and Collating Sequences.- A.1 Processor-Dependent Character Sets.- A.2 ASCII Character Set.- B Models for Numbers.- B.1 Models for Integers.- B.2 Models for Reals.- B.3 Models for Bit Manipulation.- C Index.