This chapter describes each of the Fortran statements. Each description includes a brief summary of the statement, a syntax description, a complete description and an example. The statements are listed in alphabetical order. The first section lists terms that are used throughout the chapter.
Definition of Terms
The ACCEPT statement has the same syntax as the PRINT statement and causes formatted input to be read on standard input, stdin. ACCEPT is identical to the READ statement with a unit specifier of asterisk (*).
Syntax
ACCEPT f [,iolist] ACCEPT namelist
Examples
ACCEPT *, IA, ZA ACCEPT 99, I, J, K ACCEPT SUM 99 FORMAT(I2, I4, I3)
The ALLOCATE statement allocates storage for each pointer-based variable and allocatable common block which appears in the statement. Allocate also declares storage for deferred-shape arrays.
Syntax
ALLOCATE ( name[, name ] ... [ , STAT= var ] )
Description
For a pointer based variable, its associated pointer variable is defined with the address of the allocated memory area. If the specifier STAT= is present, successful execution of the ALLOCATE statement causes the status variable to be defined with a value of zero. If an error occurs during execution of the statement and the specifier STAT= is present, the status variable is defined to have the integer value one. If an error occurs and the specifier STAT= is not present, program execution is terminated.
A dynamic, or allocatable COMMON block is a common block whose storage is not allocated until an explicit ALLOCATE statement is executed.
For a deferred-shape array, the ALLOCATE statement must include the bounds of the array. Refer to the examples for details.
Examples
COMMON P, N, MFor a deferred shape array, the allocate must include the bounds of the array.
POINTER (P, A(N,M))
COMMON, ALLOCATABLE /ALL/X(10), Y
ALLOCATE (/ALL/, A, STAT=IS)
PRINT *, IS
X(5) = A(2, 1)
DEALLOCATE (A)
DEALLOCATE (A, STAT=IS)
PRINT *, 'should be 1', IS
DEALLOCATE (/ALL/)
REAL A(:,:) ... ALLOCATE (A(1:11, M:N))
The ASSIGN statement assigns a statement label to a variable.
Syntax
ASSIGN a TO ba is the statement label.
b is an integer variable.
Description
Executing an ASSIGN statement assigns a statement label to an integer variable. This is the only way that a variable may be defined with a statement label value. The statement label must be:
Example
ASSIGN 40 TO K
GO TO K
40 L = P + I + 56
When a BACKSPACE statement is executed the file connected to the specified unit is positioned before the preceding record.
Syntax
BACKSPACE unit BACKSPACE ([UNIT=]unit [,ERR=errs] [, IOSTAT=ios])
Description
If there is no preceding record the position of the file is not changed. A BACKSPACE statement cannot be executed on a file that does not exist. You must not issue a BACKSPACE statement for a file that is open for direct or append access.
Examples
BACKSPACE 4 BACKSPACE ( UNIT=3 ) BACKSPACE ( 7, IOSTAT=IOCHEK, ERR=50 )
The BLOCK DATA statement introduces a module that sets up initial values in COMMON blocks. No executable statements are allowed in a BLOCK DATA module.
Syntax
BLOCK DATA [name]
Example
BLOCK DATA
COMMON /SIDE/ BASE, ANGLE, HEIGHT, WIDTH
INTEGER SIZE
PARAMETER (SIZE=100)
INTEGER BASE(0:SIZE)
REAL WIDTH(0:SIZE), ANGLE(0:SIZE)
DATA/(BASE(I),I=0,SIZE)/SIZE*-1,-1/,
+ (WIDTH(I),I=0,SIZE)/SIZE*0.0,0.0/
END
The BYTE statement establishes the data type of a variable by explicitly attaching the name of a variable to a 1-byte integer. This overrides the implication of data typing by the initial letter of a symbolic name.
Syntax
BYTE name [/clist/], ...
Description
Byte statements may be used to dimension arrays explicitly in the same way as the DIMENSION statement. BYTE declaration statements must not be labeled.
Example
BYTE TB3, SEC, STORE (5,5)
The CALL statement transfers control to a subroutine.
Syntax
CALL subroutine [([ argument [, argument]...])]
Description
Actual arguments can be expressions including: constants, scalar variables, function references and arrays.
@ Actual arguments can also be alternate return specifiers. Alternate return specifiers are labels prefixed by asterisks (*) or ampersands (&) (the ampersand is an extension from Fortran 77).
Recursive calls are allowed using the -Mrecursive command-line option.@
Examples
CALL CRASH ! no arguments
CALL BANG(1.0) ! one argument
CALL WALLOP(V, INT) ! two arguments
CALL ALTRET(I, *10, *20)
SUBROUTINE ONE
DIMENSION ARR ( 10, 10 )
REAL WORK
INTEGER ROW, COL
PI=3.142857
CALL EXPENS(ARR,ROW,COL,WORK,SIN(PI/2)+3.4)
RETURN
END
The CHARACTER statement establishes the data type of a variable by explicitly attaching the name of a variable to a character data type. This overrides the implication of data typing by the initial letter of a symbolic name.
Syntax
CHARACTER [*len][,] name [dimension] [*len] [/clist/], ...
Description
Character type declaration statements may be used to dimension arrays explicitly in the same way as the DIMENSION statement. Type declaration statements must not be labeled. Note: The data type of a symbol may be explicitly declared only once. It is established by type declaration statement, IMPLICIT statement or by predefined typing rules. Explicit declaration of a type overrides any implicit declaration. An IMPLICIT statement overrides predefined typing rules.
Examples
CHARACTER A*4, B*6, CA is 4 and B is 6 characters long and C is 1 character long.
The CLOSE statement terminates the connection of the specified file to a unit.
Syntax
CLOSE ([UNIT=] u [,IOSTAT=ios] [,ERR= errs ]
[,STATUS= sta] [,DISPOSE= sta] [,DISP= sta])
Description
A unit may be the subject of a CLOSE statement from within any module. If the unit specified does not exist or has no file connected to it the use of the CLOSE statement has no effect. Provided the file is still in existence it may be reconnected to the same or a different unit after the execution of a CLOSE statement. Note that an implicit CLOSE is executed when a program stops.
Example
In the following example the file on UNIT 6 is closed and deleted.
CLOSE(UNIT=6,STATUS='DELETE')
The COMMON statement defines contiguous blocks of storage. Each block is identified by a symbolic name and the order of variables and arrays is defined in the COMMON block containing them. There are two forms of the COMMON statement, a static form and a dynamic form.
Syntax
COMMON /name/nlist [, /name/nlist]...
@ COMMON [,ALLOCATABLE] /name/nlist [,/name/nlist]...
Description (static COMMON)
The name of the COMMON block need not be supplied; this is the Fortran BLANK COMMON feature. In this case the compiler will use a default name which is implementation specific. There can be several COMMON block statements of the same name in a module; these are effectively treated as one statement, with variables and array addresses concatenated from one COMMON statement of the same name to the next. This is an alternative to the use of continuation lines when declaring a common block with many symbols.
Common blocks with the same name that are declared in different modules share the same storage area when combined into one executable program.
Example (static COMMON)
DIMENSION R(10)This declares a common block of data memory called HOST where A will be held in the first memory location, R(1)... R(10) will be held in the next ten locations, Q(1)... Q(3) in the next three and U in the fifteenth location. Note the different types of declaration used for R (declared in a DIMENSION statement) and Q (declared in the COMMON statement). The declaration of HOST in a SUBROUTINE in the same executable program will share the same data area.
COMMON /HOST/ A, R, Q(3), U
SUBROUTINE DEMOIf the main program has the common block declaration as in the previous example, the COMMON statement in the subroutine causes STORE(1) to correspond to A, STORE(2) to correspond to R(1), STORE(3) to correspond to R(2), and so on through to STORE(15) corresponding to the variable U.
COMMON/HOST/STORE(15)
.
.
.
RETURN
END
You can name records within a COMMON block. Because the storage requirements of records are machine-dependent, the size of a COMMON block containing records may vary between machines. Note that this may also affect subsequent equivalence associations to variables within COMMON blocks that contain records.
@ Both character and non-character data may reside in one COMMON block. Data is aligned within the COMMON block in order to conform to machine-dependent alignment requirements.
A COMMON block may be data initialized in more than one program unit if the existing system environment allows it (note that COFF-based systems do not). It is up to the programmer to make sure that data within one COMMON block is not initialized more than once.
Blank COMMON may be data initialized.
Description (dynamic COMMON) @
A dynamic, or allocatable, COMMON block is a common block whose storage is not allocated until an explicit ALLOCATE statement is executed.
If the ALLOCATABLE attribute is present, all named COMMON blocks appearing in the COMMON statement are marked as allocatable. Like a normal COMMON statement, the name of an allocatable COMMON block may appear in more than one COMMON statement. Note that the ALLOCATABLE attribute need not appear in every COMMON statement.
The following restrictions apply to the dynamic COMMON statement:
Example (dynamic COMMON)
COMMON, ALLOCATABLE /ALL1/ A, B, /ALL2/ AA, BBThis declares the following variables:
COMMON /STAT/ D, /ALL1/ C
AA = B * D
The COMPLEX statement establishes the data type of a variable by explicitly attaching the name of a variable to a complex data type. This overrides the implication of data typing by the initial letter of a symbolic name.
Syntax
COMPLEX name [*n] [dimensions] [/clist/] [, name] [/clist/] ...
Description
COMPLEX statements may be used to dimension arrays explicitly in the same way as the DIMENSION statement. COMPLEX statements must not be labeled. Note: The data type of a symbol may be explicitly declared only once. It is established by type declaration statement, IMPLICIT statement or by predefined typing rules. Explicit declaration of a type overrides any implicit declaration. An IMPLICIT statement overrides predefined typing rules.
The default size of a COMPLEX variable is 8 bytes. With the -Mr8 option, the default size of a COMPLEX variable is 16 bytes.
Example
COMPLEX CURRENT
This CONTINUE statement passes control to the next statement. It is supplied mainly to overcome the problem that transfer of control statements are not allowed to terminate a DO loop.
Syntax
CONTINUE
Example
DO 100 I = 1,10
SUM = SUM + ARRAY (I)
IF(SUM .GE. 1000.0) GOTO 200
100 CONTINUE
200 ...
The DATA statement assigns initial values to variables before execution.
Syntax
DATA vlist/dlist/[[, ]vlist/dlist/]...
n*constant-value
Example
REAL A, B, C(3), D(2) DATA A, B, C(1), D /1.0, 2.0, 3.0, 2*4.0/This performs the following initialization:
A = 1.0 B = 2.0 C(1) = 3.0 D(1) = 4.0 D(2) = 4.0
The DEALLOCATE statement causes the memory allocated for each pointer-based variable or allocatable COMMON block that appears in the statement to be deallocated (freed). Deallocate also deallocates storage for deferred-shape arrays.
Syntax
DEALLOCATE ( al [, a1 ] ... [ , STAT= var ] )Where:
Description
An attempt to deallocate a pointer-based variable or an allocatable COMMON block which was not created by an ALLOCATE statement results in an error condition.
If the specifier STAT= is present, successful execution of the statement causes var to be defined with the value of zero. If an error occurs during the execution of the statement and the specifier STAT= is present, the status variable is defined to have the integer value one. If an error occurs and the specifier STAT= is not present, program execution is terminated.
Examples
COMMON P, N, M
POINTER (P, A(N,M))
COMMON, ALLOCATABLE /ALL/X(10), Y
ALLOCATE (/ALL/, A, STAT=IS)
PRINT *, IS
X(5) = A(2, 1)
DEALLOCATE (A)
DEALLOCATE (A, STAT=IS)
PRINT *, 'should be 1', IS
DEALLOCATE (/ALL/)
The DECODE statement transfers data between variables or arrays in internal storage and translates that data from character form to internal form, according to format specifiers. Similar results can be accomplished using internal files with formatted sequential READ statements.
Syntax
DECODE (c, f, b [ ,IOSTAT= ios ] [, ERR= errs]) [ list ]
The DIMENSION statement defines the number of dimensions in an array and the number of elements in each dimension.
Syntax
DIMENSION name ([lb:]ub[,[lb:]ub]...) [,name([lb:]ub[,[lb:]ub]...)]
Description
DIMENSION can be used in a subroutine to establish an argument as an array, and in this case the declarator can use expressions formed from integer variables and constants to establish the dimensions (adjustable arrays). Note however that these integer variables must be either arguments or declared in COMMON; they cannot be local. Note that in this case the function of DIMENSION is merely to supply a mapping of the argument to the subroutine code, and not to allocate storage.
If an array is a dummy argument its last dimension may be a * (assumed size array)
The typing of the array in a DIMENSION statement is defined by the initial letter of the array name in the same way as variable names. The letters I,J,K,L,M and N imply that the array is of INTEGER type and an array with a name starting with any of the letters A to H and O to Z will be of type REAL, unless overridden by an IMPLICIT or type declaration statement. Arrays may appear in type declaration and COMMON statements but the array name can appear in only one array declaration.
DIMENSION statements must not be labeled.
Example
DIMENSION ARRAY1(3:10), ARRAY2(3,-2:2)This specifies ARRAY1 as a vector having eight elements with the lower bound of 3 and the upper bound of 10.
ARRAY2 as a matrix of two dimensions having fifteen elements. The first dimension has three elements and the second has five with bounds from -2 to 2.
CHARACTER B(0:20)*4sets up an array B with 21 character elements each having a length of four characters. Note that the array has been dimensioned in a type declaration statement and therefore cannot subsequently appear in a DIMENSION statement.
The DOUBLE COMPLEX statement establishes the data type of a variable by explicitly attaching the name of a variable to a double complex data type. This overrides the implication of data typing by the initial letter of a symbolic name.
Syntax
DOUBLE COMPLEX name [/clist/] [, name] [/clist/]...
Description
Type declaration statements may be used to dimension arrays explicitly in the same way as the DIMENSION statement. Type declaration statements must not be labeled. Note: The data type of a symbol may be explicitly declared only once. It is established by type declaration statement, IMPLICIT statement or by predefined typing rules. Explicit declaration of a type overrides any implicit declaration. An IMPLICIT statement overrides predefined typing rules.
The default size of a DOUBLE COMPLEX variable is 16 bytes. With the -Mr8 option, the default size of a DOUBLE COMPLEX variable is also 16 bytes.
Examples
DOUBLE COMPLEX CURRENT, NEXT
The DOUBLE PRECISION statement establishes the data type of a variable by explicitly attaching the name of a variable to a double precision data type. This overrides the implication of data typing by the initial letter of a symbolic name.
Syntax
DOUBLE PRECISION name [/clist/] [, name] [/clist/]...
Description
Type declaration statements may be used to dimension arrays explicitly in the same way as the DIMENSION statement. Type declaration statements must not be labeled. Note: The data type of a symbol may be explicitly declared only once. It is established by type declaration statement, IMPLICIT statement or by predefined typing rules. Explicit declaration of a type overrides any implicit declaration. An IMPLICIT statement overrides predefined typing rules.
The default size of a DOUBLE PRECISION variable is 8 bytes.
Examples
DOUBLE PRECISION PLONG
The DO statement introduces an iterative loop and specifies the loop control index and parameters.
Syntax
DO [label [,]] i = el, e2 [, e3]
Description
@ If the optional label, label is not included, the DO statement must be terminated by an END DO statement.
The DO loop consists of all the executable statements after the specifying DO statement up to and including the labeled statement, called the terminal statement. The label is optional. If omitted, the terminal statement of the loop is an END DO statement.
@ END DO may be used to terminate the DO loop even if a label is specified.
Before execution of a DO loop, an iteration count is initialized for the loop. This value is the number of times the DO loop is executed, and is
INT((e2-e1+e3)/e3)If the value obtained is negative or zero that the loop is not executed.
The DO loop is executed first with i taking the value e1, then the value (e1+e3), then the value (e1+e3+e3), etc.
It is possible to jump out of a DO loop and jump back in, as long as the do index variable has not been adjusted.
@ Nested DO loops may share the same labeled terminal statement if required. They may not share an END DO statement.
In a nested DO loop, it is legal to transfer control from an inner loop to an outer loop. It is illegal, however, to transfer into a nested loop from outside the loop.
Example
DO 100 J = -10,10
DO 100 I = -5,5
100 SUM = SUM + ARRAY (I,J)
The DO WHILE statement introduces a logical do loop and specifies the loop control expression.
The DO WHILE statement executes for as long as the logical expression e continues to be true when tested at the beginning of each iteration. If e is false, control transfers to the statement following the loop.
Syntax
DO [label[,]] WHILE expressionThe end of the loop is specified in the same way as for an iterative loop, either with a labeled statement or an END DO.
Description
The logical-expression is evaluated. If it is .FALSE., the loop is not entered. If it is .TRUE., the loop is executed once. Then logical-expression is evaluated again, and the cycle is repeated until the expression evaluates .FALSE..
The ELSE statement begins an ELSE block of an IF block and encloses a series of statements that are conditionally executed.
Syntax
IF logical expression THENThe ELSE section is optional and may occur only once. Other IF blocks may be nested within the statements section of an ELSE block.
statements
ELSE IF logical expression THEN
statements
ELSE
statements
ENDIF
Example
IF (I.LT.15) THEN
M = 4
ELSE
M=5
ENDIF
The ELSE IF statement begins an ELSE IF block of an IF block series and encloses statements that are conditionally executed.
Syntax
IF logical expression THENThe ELSE IF section is optional and may be repeated any number of times. Other IF blocks may be nested within the statements section of an ELSE IF block.
statements
ELSE IF logical expression THEN
statements
ELSE
statements
ENDIF
Example
IF (I.GT.70) THEN
M=1
ELSE IF (I.LT.5) THEN
M=2
ELSE IF (I.LT.16) THEN
M=3
ENDIF
The ENCODE statement transfers data between variables or arrays in internal storage and translates that data from internal to character form, according to format specifiers. Similar results can be accomplished using internal files with formatted sequential WRITE statements.
Syntax
ENCODE (c,f,b[,IOSTAT=ios] [,ERR=errs])[list]
This END statement terminates a module. It may be the last statement in a compilation or it may be followed by a new module.
Syntax
END
Description
The END statement is executable, and has the same effect as a RETURN statement in a SUBROUTINE or FUNCTION, or the effect of a STOP statement in a PROGRAM module.
The END DO statement terminates a DO or DO WHILE loop.
Syntax
END DO
Description
The END DO statement terminates an indexed DO or DO WHILE statement which does not contain a terminal-statement label.
The END DO statement may also be used as a labeled terminal statement if the DO or DO WHILE statement contains a terminal-statement label.
When an END FILE statement is executed an endfile record is written to the file as the next record. The file is then positioned after the endfile record. Note that only records written prior to the endfile record can be read later.
Syntax
END FILE u END FILE ([UNIT=]u, list)
Examples
END FILE(20) END FILE(UNIT=34, IOSTAT=IOERR, ERR=140)
The END IF statement terminates an IF. ELSE or ELSE IF block.
Syntax
END IF
Description
The END IF statement terminates an IF block. Thre must be a matching block IF statement (at the same IF level) earlier in the same subprogram.
The END MAP statement terminates a MAP declaration.
Syntax
END MAP
Description
See the MAP statement for details.
The END STRUCTURE statement terminates a STRUCTURE declaration.
Syntax
END STRUCTURE
Description
See the STRUCTURE statement for details.
The END UNION statement terminates a UNION declaration.
Syntax
END UNION
Description
See the UNION statement for details.
The ENTRY statement allows a subroutine or function to have more than one entry point.
Syntax
ENTRY name [(variable, variable...)]
Description
The name of an ENTRY must not be used as a dummy argument in a FUNCTION, SUBROUTINE or ENTRY statement, nor may it appear in an EXTERNAL statement.
Within a function a variable name which is the same as the entry name may not appear in any statement that precedes the ENTRY statement, except in a type statement.
If name is of type character the names of each entry in the function and the function name must be of type character. If the function name or any entry name has a length of (*) all such names must have a length of (*); otherwise they must all have a length specification of the same integer value.
A name which is used as a dummy argument must not appear in an executable statement preceding the ENTRY statement unless it also appears in a FUNCTION, SUBROUTINE or ENTRY statement that precedes the executable statement. Neither must it appear in the expression of a statement function unless the name is also a dummy argument of the statement function, or appears in a FUNCTION or SUBROUTINE statement, or in an ENTRY statement that precedes the statement function statement.
If a dummy argument appears in an executable statement, execution of that statement is only permitted during the execution of a reference to the function or subroutine if the dummy argument appears in the dummy argument list of the procedure name referenced.
When a subroutine or function is called using the entry name, execution begins with the statement immediately following the ENTRY statement. If a function entry has no dummy arguments the function must be referenced by name() but a subroutine entry without dummy arguments may be called with or without the parentheses after the entry name.
An entry may be referenced from any module except the one in which it is defined.
The order, type, number and names of dummy arguments in an ENTRY statement can be different from those used in the FUNCTION, SUBROUTINE or other ENTRY statements in the same module but each reference must use an actual argument list which agrees in order, number and type with the dummy argument list of the corresponding FUNCTION, SUBROUTINE or ENTRY statement. When a subroutine name or an alternate return specifier is used as an actual argument there is no need to match the type.
Entry names within a FUNCTION subprogram need not be of the same data type as the function name, but they all must be consistent within one of the following groups of data types:
Example
FUNCTION SUM(TALL,SHORT,TINY)When the calling program calls the function SUM it can do so in one of three ways depending on which ENTRY point is desired.
.
SUM=TALL-(SHORT+TINY)
RETURN
ENTRY SUM1(X,LONG,TALL,WIDE,NARROW)
.
.
SUM1=(X*LONG)+(TALL*WIDE)+NARROW
RETURN
ENTRY SUM2(SHORT,SMALL,TALL,WIDE)
.
.
SUM2=(TALL-SMALL)+(WIDE-SHORT)
RETURN
END
For example if the call is:
Z=SUM2(LITTLE,SMALL,BIG,HUGE)the ENTRY point is SUM2.
If the call is:
Z=SUM(T,X,Y)the ENTRY point is SUM and so on.
The EQUIVALENCE statement allows two or more named regions of data memory to share the same start address.
Syntax
EQUIVALENCE (list)[,(list)...]
Description
@ An array element may be identified with a single subscript in an EQUIVALENCE statement even though the array is defined to be a multidimensional array.
@ Equivalence of character and non-character data is allowed as long as misalignment of non-character data does not occur.
Records and record fields cannot be specified in EQUIVALENCE statements.
The statement can be used to make a single region of data memory have different types, so that for instance the imaginary part of a complex number can be treated as a real value. make arrays overlap, so that the same region of store can be dimensioned in several different ways.
Example
COMPLEX NUMIn the above example QWER(1) is the real part of NUM and QWER(2) is the imaginary part. EQUIVALENCE statements are illegal if there is any attempt to make a mapping of data memory inconsistent with its linear layout.
REAL QWER(2)
EQUIVALENCE (NUM,QWER(1))
The EXTERNAL statement identifies a symbolic name as an external or dummy procedure. This procedure can then be used as an actual argument.
Syntax
EXTERNAL proc [,proc]..
Description
If an intrinsic function appears in an EXTERNAL statement an intrinsic function of the same name cannot then be referenced in the module. A symbolic name can appear only once in all the EXTERNAL statements of a module.
The FORMAT statement specifies format requirements for input or output.
Syntax
label FORMAT (list-items)
Description
Refer to section 4.4.2, Format Specificatins.
Examples
WRITE (6,90) NPAGE
90 FORMAT('1PAGE NUMBER ',I2,16X,'SALES REPORT, Cont.')
produces:
PAGE NUMBER SALES REPORT, Cont.The following example shows use of the tabulation specifier T:
PRINT 25produces:
25 FORMAT (T41,'COLUMN 2',T21,'COLUMN 1')
COLUMN 1 COLUMN 2
DIMENSION A(6)produces:
DO 10 I = 1,6
10 A(I) = 25.
TYPE 100,A
100 FORMAT(' ',F8.2,2PF8.2,F8.2) ! ' '
C ! gives single spacing
25.00 2500.00 2500.00 2500.00 2500.00 2500.00Note that the effect of the scale factor continues until another scale factor is used.
The function statement introduces a module; the statements that follow all apply to the function itself and are laid out in the same order as those of a PROGRAM module.
Syntax
[type] FUNCTION name [*n] ([argument [,argument]...])
Description
The statements and names in the module apply only to the function, except for subroutine or function references and the names of COMMON blocks. The module must be terminated by an END statement.
A function produces a result; this allows a function reference to appear in an expression, where the result is assumed to replace the actual reference. The symbolic name of the function must appear as a variable in the module. The value of this variable, on exit from the function, is the result of the function. The result is undefined if the variable has not been defined.
The type of a FUNCTION refers to the type of its result.
Recursion is allowed if the -Mrecursive option is used on the command-line.
Examples
FUNCTION FRED(A,B,C)
REAL X
.
.
END
FUNCTION EMPTY() ! Note parentheses
END PROGRAM FUNCALL
.
.
SIDE=TOTAL(A,B,C)
.
.
END
FUNCTION TOTAL(X,Y,Z)
.
.
END FUNCTION AORB(A,B)
IF(A-B)1,2,3
1 AORB = A
RETURN
2 AORB = B
RETURN
3 AORB = A + B
RETURN
END
The assigned GOTO statement transfers control so that the statement identified by the statement label is executed next.
Syntax
GOTO integer-variable-name[[,] (list)]
Examples
ASSIGN 50 TO K
GO TO K(50,90)
90 G=D**5
.
.
50 F=R/T
The computed GOTO statement allows transfer of control to one of a list of labels according to the value of an expression.
Syntax
GOTO (list) [,] expression
Example
READ *, A, B
GO TO (50,60,70)A
WRITE (*, 10) A, B
10 FORMAT (' ', I3, F10.4, 5X, 'A must be 1, 2
+ or 3')
STOP
50 X=A**B ! Come here if A has the value 1
GO TO 100
60 X=(A*56)*(B/3) !Come here if A is 2
GO TO 100
70 X=A*B ! Come here if A has the value 3
100 WRITE (*, 20) A, B, X
20 FORMAT (' ', I3, F10.4, 5X, F10.4)
The GOTO statement unconditionally transfers control to the statement with the label label. The statement label label must be declared within the code of the module containing the GOTO statement and must be unique within that module.
Syntax
GOTO label
Example
TOTAL=0.0
30 READ *, X
IF (X.GE.0) THEN
TOTAL=TOTAL+X
GOTO 30
END IF
The arithmetic IF statement transfers control to one of three labeled statements. The statement chosen depends upon the value of an arithmetic expression.
Syntax
IF (arithmetic-expression) label-1, label-2, label-3Control transfers to label-1, label-2 or label-3 if the result of the evaluation of the arithmetic-expression is less than zero, equal to zero or greater than zero respectively.
Example
IF X 10, 20, 30if X is less than zero then control is transferred to label 10.
if X equals zero then control is transferred to label 20.
if X is greater than zero then control is transferred to label 30.
The block IF statement consists of a series of statements that are conditionally executed.
Syntax
IF logical expression THENThe ELSE IF section is optional and may be repeated any number of times. Other IF blocks may be nested within the statements section of an IF block.
statements
ELSE IF logical expression THEN
statements
ELSE
statements
ENDIF
Example
IF (I.GT.70) THEN
M=1
ELSE IF (I.LT.5) THEN
M=2
ELSE IF (I.LT.16) THEN
M=3
ENDIF
IF (I.LT.15) THEN
M = 4
ELSE
M=5
ENDIF
The logical IF statement executes or does not execute a statement based on the value of a logical expression.
Syntax
IF (logical-expression) statement
Examples
IF(N .LE. 2) GOTO 27 IF(HIGH .GT. 1000.0 .OR. HIGH .LT. 0.0) HIGH=1000.0
The IMPLICIT statement redefines the implied data type of symbolic names from their initial letter. Without the use of the IMPLICIT statement all names that begin with the letters I,J,K,L,M or N are assumed to be of type integer and all names beginning with any other letters are assumed to be real.
Syntax
IMPLICIT spec (a[,a]...) [,spec (a[,a]...)]
@ IMPLICIT NONE
Description
IMPLICIT statements must not be labeled.
Symbol names may begin with a dollar sign ($) or underscore (_) character, both of which are of type REAL by default. In an IMPLICIT statement, these characters may be used in the same manner as other characters, but they cannot be used in a range specification.
The IMPLICIT NONE statement specifies that all symbolic names must be explicitly declared, otherwise an error is reported. If IMPLICT NONE is used, no other IMPLICIT can be present.
Examples
IMPLICIT REAL (L,N) IMPLICIT INTEGER (S,W-Z) IMPLICIT INTEGER (A-D,$,_)
The INCLUDE statement directs the compiler to start reading from another file.
Syntax
INCLUDE 'filename[/[NO]LIST]' INCLUDE "filename[/[NO]LIST]"The INCLUDE statement may be nested to a depth of 20 and can appear anywhere within a program unit as long as Fortran's statement-ordering restrictions are not violated.
The qualifiers /LIST and /NOLIST can be used to control whether the include file is expanded in the listing file (if generated).
Note that there is no support for VAX/VMS text libraries or the module_name pathname qualifier that exists in the VAX/VMS version of the INCLUDE statement.
Either single or double quotes may be used.
If the final component of the file pathname is /LIST or /NOLIST, the compiler will assume it is a qualifier, unless an additional qualifier is supplied.
The filename and the /LIST or /NOLISt qualifier may be separated by blanks.
Example
INCLUDE '/mypath/list /list'This includes a file named /mypath/list and expands it in the listing.
An INQUIRE statement has two forms and is used to inquire about the current properties of a particular file or the current connections of a particular unit. INQUIRE may be executed before, during or after a file is connected to a unit.
Syntax
INQUIRE (FILE=filename, list) INQUIRE ([UNIT=]unit,list)list of specifiers is as follows:
Description
When an INQUIRE by file statement is executed the following specifiers will only be assigned values if the file name is acceptable:
nmd, fn, seq, dir, fmt and unf. num is defined, and acc, fm, rcl, nr and blnk may become defined only if od is defined as .TRUE..
When an INQUIRE by unit statement is executed the specifiers num, nmd, fn, acc, seq, dir, fm, fmt, unf, rcl, nr and blnk are assigned values provided that the specified unit exists and a file is connected to that unit. Should an error condition occur during the execution of an INQUIRE statement all the specifiers except ios become undefined.
The INTEGER statement establishes the data type of a variable by explicitly attaching the name of a variable to an integer data type. This overrides the implication of data typing by the initial letter of a symbolic name.
Syntax
INTEGER [*n] [,] name [*n] [dimensions] [/clist/] [, name [*n][dimensions] [/clist/]]...
Description
Integer type declaration statements may be used to dimension arrays explicitly in the same way as the DIMENSION statement. INTEGER statements must not be labeled. Note: The data type of a symbol may be explicitly declared only once. It is established by type declaration statement, IMPLICIT statement or by predefined typing rules. Explicit declaration of a type overrides any implicit declaration. An IMPLICIT statement overrides predefined typing rules.
The default size of an INTEGER variable is 4 bytes. With the -Mnoi4 option, the default size of an INTEGER variable is 2 bytes.
Example
INTEGER TIME, SECOND, STORE (5,5)
An INTRINSIC statement identifies a symbolic name as an intrinsic function and allows it to be used as an actual argument.
Syntax
INTRINSIC func [,func]
Description
Do not use any of the following functions in INTRINSIC statements:
When a specific name of an intrinsic function is used as an actual argument in a module it must appear in an INTRINSIC statement in that module. If the name used in an INTRINSIC statement is also the name of a generic intrinsic function, it retains its generic properties. A symbolic name can appear only once in all the INTRINSIC statements of a module and cannot be used in both an EXTERNAL and INTRINSIC statement in a module.
The following example illustrates the use of INTRINSIC and EXTERNAL:
EXTERNAL MYOWN
INTRINSIC SIN, COS
.
.
CALL TRIG (ANGLE,SIN,SINE)
.
CALL TRIG (ANGLE,MYOWN,COTANGENT)
.
CALL TRIG (ANGLE,COS,SINE) SUBROUTINE TRIG (X,F,Y)
Y=F(X)
RETURN
END
FUNCTION MYOWNIn this example, when TRIG is called with a second argument of SIN or COS the function reference F(X) references the intrinsic functions SIN and COS; however when TRIG is called with MYOWN as the second argument F(X) references the user function MYOWN.
MYOWN=COS(X)/SIN(X)
RETURN
END
The LOGICAL statement establishes the data type of a variable by explicitly attaching the name of a variable to an integer data type. This overrides the implication of data typing by the initial letter of a symbolic name.
Syntax
LOGICAL [*n] [,] name [*n] [dimensions] [/clist/][, name] [*n][dimensions] [/clist/]...
Description
Integer type declaration statements may be used to dimension arrays explicitly in the same way as the DIMENSION statement. Type declaration statements must not be labeled. Note: The data type of a symbol may be explicitly declared only once. It is established by type declaration statement, IMPLICIT statement or by predefined typing rules. Explicit declaration of a type overrides any implicit declaration. An IMPLICIT statement overrides predefined typing rules.
The default size of an LOGICAL variable is 4 bytes. With the -Mnoi4 option, the default size of an LOGICAL variable is 2 bytes.
Example
LOGICAL TIME, SECOND, STORE (5,5)
A union declaration is initiated by a UNION statement and terminated by an END UNION statement. Enclosed within these statements are one or more map declarations, initiated and terminated by MAP and END MAP statements, respectively. Each unique field or group of fields is defined by a separate map declaration.
Syntax
MAP
field_declaration
[field_declaration]
...
[field_declaration]
END MAP
Description
Data can be initialized in field declaration statements in union declarations. Note, however, it is illegal to initialize multiple map declarations in a single union.
The size of the shared area for a union declaration is the size of the largest map defined for that union. The size of a map is the sum of the sizes of the field(s) declared within it plus the space reserved for alignment purposes.
Manipulating data using union declarations is similar to what happens using EQUIVALENCE statements. However, union declarations are probably more similar to union declarations for the language C. The main difference is that the language C requires one to associate a name with each map (union). Fortran field names must be unique within the same declaration nesting level of maps.
Example
The following is an example of RECORD, STRUCTURE and UNION usage. The size of each element of the recarr array would be the size of typetag (4 bytes) plus the size of the largest MAP - the employee map (24 bytes).
STRUCTURE /account/
INTEGER typetag ! Tag to determine defined map.
UNION
MAP ! Structure for an employee
CHARACTER*12 ssn ! Social Security Number
REAL*4 salary
CHARACTER*8 empdate ! Employment date
END MAP
MAP ! Structure for a customer
INTEGER*4 acct_cust
REAL*4 credit_amt
CHARACTER*8 due_date
END MAP
MAP ! Structure for a supplier
INTEGER*4 acct_supp
REAL*4 debit_amt
BYTE num_items
BYTE items(12) ! Items supplied
END MAP
END UNION
END STRUCTURE RECORD /account/ recarr(1000)
The NAMELIST statement allows for the definition of namelist groups for namelist-directed I/O.
Syntax
NAMELIST /group-name/ namelist [[,] /group-name/ namelist ]...
Example
In the following example a named group PERS consits of a name, an account, and a value.
CHARACTER*12 NAME
INTEGER*$ ACCOUNT
REAL*4 VALUE
NAMELIST /PERS/ NAME, ACCOUNT, VALUE
The OPEN statement can be used to do the following: connect an existing file to a unit; create and connect a file to a unit; create a file that is preconnected; change certain specifiers of a connection between a file and a unit
Syntax
OPEN ( list )
[UNIT=] uwhere the UNIT= is optional and the external unit specifier u is an integer.
In addition list may contain one of each of the following specifiers in any order.
Description
The record length, RECL=, must be specified if a file is connected for direct access and optionally one of each of the other specifiers may be used. RECL is ignored if the access method is sequential.
The unit specified must exist and once connected by an OPEN statement can be referenced in any module of the executable program. If a file is connected to a unit it cannot be connected to a different unit by the OPEN statement.
If a unit is connected to an existing file, execution of an OPEN statement for that file is allowed. Where FILE= is not specified the file to be connected is the same as the file currently connected. If the file specified for connection to the unit does not exist but is the same as a preconnected file, the properties specified by the OPEN statement become part of the connection. However, if the file specified is not the same as the preconnected file this has the same effect as the execution of a CLOSE statement without a STATUS= specifier immediately before the execution of the OPEN statement. When the file to be connected is the same as the file already connected only the BLANK= specifier may be different from the one currently defined.
Example
In the following example a new file, BOOK, is created and connected to unit 12 for direct formatted input/output with a record length of 98 characters. Numeric values will have blanks ignored and E1 will be assigned some positive value if an error condition exists when the OPEN statement is executed; execution will then continue with the statement labeled 20. If no error condition pertains, E1 is assigned the value zero (0) and execution continues with the next statement.
OPEN( 12, IOSTAT=E1, ERR=20, FILE='BOOK',
1BLANK='NULL', ACCESS='DIRECT', RECL=98,
1FORM='FORMATTED',STATUS='NEW')
Environment Variables
For an OPEN statement which does not contain the FILE= specifier, an environment variable may be used to specify the file to be connected to the unit. If the environment variable FORddd exists, where ddd is a 3 digit string whose value is the unit, the environment variable's value is the name of the file to be opened.
VAX/VMS Fortran
VAX/VMS introduces a number of extensions to the OPEN statement. Many of these relate only to the VMS file system and are not supported (e.g., KEYED access for indexed files). The following keywords for the OPEN statement have been added or augmented as shown below. Refer to Programming in VAX FORTRAN for additional details on these keywords.
Syntax
OPTIONS /option [/option ...]Table 3.1 shows what options are available for the OPTIONS statement.
Option
|
Action Taken
|
| CHECK=ALL
|
Enable
array bounds checking
|
| CHECK=[NO]OVERFLOW
|
None
(recognized but ignored)
|
| CHECK=[NO]BOUNDS
|
(Disable)
Enable array bounds checkinng
|
| CHECK=[NO]UNDERFLOW
|
None
|
| CHECK=NONE
|
Disable
array bounds checking
|
| NOCHECK
|
Disable
array bounds checking
|
| [NO]EXTEND_SOURCE
|
(Disable)
Enable the -Mextend option
|
| [NO]F77
|
(Disable)
Enable the -Mstandard option
|
| [NO]G_FLOATING
|
None
|
| [NO]I4
|
(Disable)
Enable the -Mi4 option
|
| [NO]RECURSIVE
|
(Disable)
Enable the -Mrecursive option
|
| [NO]REENTRANT
|
(Enable)
Disable optimizations that may result in code that is not reentrant.
|
| [NO]STANDARD
|
(Disable)
Enable the -Mstandard option
|
The following restrictions apply to the OPTIONS statement:
The PARAMETER statement gives a symbolic name to a constant.
Syntax
PARAMETER (name = expression[,name = expression...] )
Examples
PARAMETER ( PI = 3.142 ) PARAMETER ( INDEX = 1024 ) PARAMETER ( INDEX3 = INDEX * 3 )The following VAX/VMS extensions to the PARAMETER statement are fully supported:
PARAMETER p=c [,p=c]...where p is a symbolic name and c is a constant, symbolic constant, or a compile time constant expression.
The PAUSE statement stops the program's execution.
Syntax
PAUSE [character-expression | digits ]The PAUSE statement stops the program's execution. The program may be restarted later and execution will then continue with the statement following the PAUSE statement.
The POINTER statement declares a scalar variable to be a pointer variable (of type INTEGER), and another variable to be its pointer-based variable.
Syntax
POINTER (p1, v1) [, (p2, v2) ...]
Example
REAL XC(10)
COMMON IC, XC
POINTER (P, I)
POINTER (Q, X(5)) P = LOC(IC)
I = 0 ! IC gets 0 P = LOC(XC)
Q = P + 20 ! same as LOC(XC(6))
X(1) = 0 ! XC(6) gets 0 ALLOCATE (X) ! Q locates a dynamically
! allocated memory area
Restrictions
The following restrictions apply to the POINTER statement:
The PRINT statement is a data transfer output statement.
Syntax
PRINT format-identifier [, iolist] or @ PRINT namelist-group
Description
When a PRINT statement is executed the following operations are carried out : data is transferred to the standard output device from the items specified in the output list and format specification.[*] The data are transferred between the specified destinations in the order specified by the input/output list. Every item whose value is to be transferred must be defined.
The program statement specifies the entry point for the linked Fortran program.
Syntax
PROGRAM [name]
Description
The program statement specifies the entry point for the linked Fortran program. An END statement terminates the program.
Example
PROGRAM MYOWN
REAL MEAN, TOTAL
.
CALL TRIG(A,B,C,MEAN)
.
END
The READ statement is the data transfer input statement.
Syntax
READ ([unit=] u [,FMT=] format-identifier [,control-information] [iolist]
READ format-identifier [,iolist]
@ READ ([unit=] u, [NML=] namelist-group [,control-information])
Description
When a READ statement is executed the following operations are carried out : data is transferred from the standard input device to the items specified in the input and format specification.[*] The data are transferred between the specified destinations in the order specified by the input/output list. Every item whose value is to be transferred must be defined.
Example
READ(2,110) I,J,K 110 FORMAT(I2, I4, I3)
The REAL statement establishes the data type of a variable by explicitly attaching the name of a variable to a data type. This overrides the implication of data typing by the initial letter of a symbolic name.
Syntax
REAL [*n] name [*n] [dimensions] [/clist/] [, name] [*n] [dimensions][/clist/]...
Description
The REAL type declaration statements may be used to dimension arrays explicitly in the same way as the DIMENSION statement. Type declaration statements must not be labeled. Note: The data type of a symbol may be explicitly declared only once. It is established by type declaration statement, IMPLICIT statement or by predefined typing rules. Explicit declaration of a type overrides any implicit declaration. An IMPLICIT statement overrides predefined typing rules.
The default size of a REAL variable is 4 bytes. With the -Mr8 option, the default size of an REAL variable is 8 bytes.
Example
REAL KNOTS
The RECORD statement defines a user-defined aggregate data item.
Syntax
RECORD /structure_name/record_namelist
[,/structure_name/record_namelist]
... [,/structure_name/record_namelist] END RECORD
Description
You create memory storage for a record by specifying a structure name in the RECORD statement. You define the field values in a record either by defining them in the structure declaration or by assigning them with executable code.
You can access individual fields in a record by combining the parent record name, a period (.), and the field name (for example, recordname.fieldname). For records, a scalar reference means a reference to a name that resolves to a single typed data item (for example, INTEGER), while an aggregate reference means a reference that resolves to a structured data item.
Scalar field references may appear wherever normal variable or array elements may appear with the exception of the COMMON, SAVE, NAMELIST, DATA and EQUIVALENCE statements. Aggregate references may only appear in aggregate assignment statements, unformatted I/O statements, and as parameters to subprograms.
Records are allowed in COMMON and DIMENSION statements.
Example
STRUCTURE /PERSON/ ! Declare a structure to define a person
INTEGER ID
LOGICAL LIVING
CHARACTER*5 FIRST, LAST, MIDDLE
INTEGER AGE
END STRUCTURE
! Define population to be an array where each element is of
! type person. Also define a variable, me, of type person.
RECORD /PERSON/ POPULATION(2), ME
...
ME.AGE = 34 ! Assign values for the variable me to
ME.LIVING = .TRUE. ! some of the fields.
ME.FIRST = 'Steve'
ME.ID = 542124822
...
POPULATION(1).LAST = 'Jones' ! Assign the "LAST" field of
! element 1 of array population.
POPULATION(2) = ME ! Assign all the values of record
! "ME" to the record population(2)
The REDIMENSION statement dynamically defines the bounds of a deferred-shape array. After a REDIMENSION statement, the bounds of the array become those supplied in the statement, until another such statement is encountered.
Syntax
REDIMENSION name ([lb:]ub[,[lb:]ub]...) [,name([lb:]ub[,[lb:]ub]...)]...Where:
Example
REAL A(:, :)
POINTER (P, A)
P = malloc(12 * 10 * 4)
REDIMENSION A(12, 10)
A(3, 4) = 33.
The RETURN statement causes a return to the statement following a CALL when used in a subroutine, and to within the relevant arithmetic expression when used in a function.
Syntax
RETURN
RETURN alternate Statement
The alternate RETURN statement takes the following form:
RETURN expression
Example
SUBROUTINE FIX (A,B,*,*,C)
40 IF (T) 50, 60, 70
50 RETURN
60 RETURN 1
70 RETURN 2
END
PROGRAM FIXIT
CALL FIX(X, Y, *100, *200, S)
WRITE(*,5) X, S ! Come here if (T) < 0
STOP
100 WRITE(*, 10) X, Y ! Come here if (T) = 0
STOP
200 WRITE(*,20) Y, S ! Come here if (T) > 0
The REWIND statement positions the file at its beginning. The statement has no effect if the file is already positioned at the start or if the file is connected but does not exist.
Syntax
REWIND unit REWIND (unit,list)
Examples
REWIND 5 REWIND(2, ERR=30) REWIND(3, IOSTAT=IOERR)
The SAVE statement retains the definition status of an entity after a RETURN or END statement in a subroutine or function has been executed.
Syntax
SAVE [v [, v ]...]
Description
Using a common-block name, preceded and followed by a slash, ensures that all entities within that COMMON block are saved. SAVE may be used without a list, in which case all the allowable entities within the module are saved (this has the same effect as using the -Msave command-line option). Dummy arguments, names of procedures and names of entities within a common block may not be specified in a SAVE statement. Use of the SAVE statement with local variables ensures the values of the local varialbes are retained for the next invocation of the SUBROUTINE or FUNCTION. Within a main program the SAVE statement is optional and has no effect.
When a RETURN or END is executed within a subroutine or function, all entities become undefined with the exception of:
Example
PROGRAM SAFE
.
CALL KEEP
.
SUBROUTINE KEEP
COMMON /LIST/ TOP, MIDDLE
INTEGER LOCAL1.
.
SAVE /LIST/, LOCAL1
The STOP statement stops the program's execution and precludes any further execution of the program.
Syntax
STOP [character-expression | digits ]
The STRUCTURE statement defines an aggregate data type.
Syntax
STRUCTURE [/structure_name/][field_namelist]
field_declaration
[field_declaration]
... [field_declaration]
END STRUCTURE
Description
Fields within structures conform to machine-dependent alignment requirements. Alignment of fields also provides a C-like "struct" building capability and allows convenient inter-language communications. Note that aligning of structure fields is not supported by VAX/VMS Fortran.
Field names within the same declaration nesting level must be unique, but an inner structure declaration can include field names used in an outer structure declaration without conflict. Also, because records use periods to separate fields, it is not legal to use relational operators (for example, .EQ., .XOR.), logical constants (.TRUE. or .FALSE.), or logical expressions (.AND., .NOT., .OR.) as field names in structure declarations.
Fields in a structure are aligned as required by hardware and a structure's storage requirements are therefore machine-dependent. Note that VAX/VMS Fortran does no padding. Because explicit padding of records is not necessary, the compiler recognizes the %FILL intrinsic, but performs no action in response to it.
Data initialization can occur for the individual fields.
The UNION and MAP statements are supported.
The following is an example of record and structure usage.
STRUCTURE /account/
INTEGER typetag ! Tag to determine defined map.
UNION
MAP ! Structure for an employee
CHARACTER*12 ssn ! Social Security Number
REAL*4 salary
CHARACTER*8 empdate ! Employment date
END MAP
MAP ! Structure for a customer
INTEGER*4 acct_cust
REAL*4 credit_amt
CHARACTER*8 due_date
END MAP
MAP ! Structure for a supplier
INTEGER*4 acct_supp
REAL*4 debit_amt
BYTE num_items
BYTE items(12) ! Items supplied
END MAP
END UNION
END STRUCTURE RECORD /account/ recarr(1000)
The SUBROUTINE statement introduces a module. The statements that follow should be laid out in the same order as a PROGRAM module.
Syntax
SUBROUTINE name [(argument[,argument...])]
Description
The SUBROUTINE module must be terminated by an END statement. The statements and names in the module only apply to the subroutine except for subroutine or function references and the names of COMMON blocks. Dummy arguments may be specified as * which indicates that the SUBROUTINE contains alternate returns.
Recursion is allowed with the -Mrecursive option.
Example
SUBROUTINE STAR(A,B,C,*,*)Note the dummy arguments represented by the two *s.
IF (ANY) THEN
A=45
B=36.33
C=0
RETURN 1
ELSE
C=100
RETURN 2
END IF
END PROGRAM SHOWME
.
.
CALL STAR(R,S,T,*30,*40)
.
.
30 WRITE(*,10) R,S ! Come here if RETURN 1
.
.
40 WRITE(*,20) T ! Come here if RETURN 2 .
The THEN statement is part of a block IF statement and surrounds a series of statements that are conditionally executed.
Syntax
IF logical expression THENThe ELSE IF section is optional and may be repeated any number of times. Other IF blocks may be nested within the statements section of an IF block.
statements
ELSE IF logical expression THEN
statements
ELSE
statements
ENDIF
Example
IF (I.GT.70) THEN
M=1
ELSE IF (I.LT.5) THEN
M=2
ELSE IF (I.LT.16) THEN
M=3
ENDIF
IF (I.LT.15) THEN
M = 4
ELSE
M=5
ENDIF
The TYPE statement has the same syntax and effect as the PRINT statement. Refer to the PRINT entry for a description of its syntax and a description.
A union declaration is a multistatement declaration defining a data area that can be shared intermittently during program execution by one or more fields or groups of fields. It declares groups of fields that share a common location within a structure. Each group of fields within a union declaration is declared by a map declaration, with one or more fields per map declaration.
Syntax
UNIONThe format of the map_declaration is as follows:
map_declaration
[map_declaration]
...
[map_declaration]
END UNION
MAP
field_declaration
[field_declaration]
...
[field_declaration]
END MAP
Description
Union declarations are used when one wants to use the same area of memory to alternately contain two or more groups of fields. Whenever one of the fields declared by a union declaration is referenced in a program, that field and any other fields in its map declaration become defined. Then, when a field in one of the other map declarations in the union declaration is referenced, the fields in that map declaration become defined, superseding the fields that were previously defined.
A union declaration is initiated by a UNION statement and terminated by an END UNION statement. Enclosed within these statements are one or more map declarations, initiated and terminated by MAP and END MAP statements, respectively. Each unique field or group of fields is defined by a separate map declaration. The format of a UNION statement is as follows:
Data can be initialized in field declaration statements in union declarations. Note, however, it is illegal to initialize multiple map declarations in a single union.
The size of the shared area for a union declaration is the size of the largest map defined for that union. The size of a map is the sum of the sizes of the field(s) declared within it plus the space reserved for alignment purposes.
Manipulating data using union declarations is similar to what happens using EQUIVALENCE statements. However, union declarations are probably more similar to union declarations for the language C. The main difference is that the language C requires one to associate a name with each map (union). Fortran field names must be unique within the same declaration nesting level of maps.
The following is an example of RECORD, STRUCTURE and UNION usage. The size of each element of the recarr array would be the size of typetag (4 bytes) plus the size of the largest MAP - the employee map (24 bytes).
STRUCTURE /account/
INTEGER typetag ! Tag to determine defined map.
UNION
MAP ! Structure for an employee
CHARACTER*12 ssn ! Social Security Number
REAL*4 salary
CHARACTER*8 empdate ! Employment date
END MAP
MAP ! Structure for a customer
INTEGER*4 acct_cust
REAL*4 credit_amt
CHARACTER*8 due_date
END MAP
MAP ! Structure for a supplier
INTEGER*4 acct_supp
REAL*4 debit_amt
BYTE num_items
BYTE items(12) ! Items supplied
END MAP
END UNION
END STRUCTURE RECORD /account/ recarr(1000)
The VOLATILE statement inhibits all optimizations on the variables, arrays and common blocks that it identifies.
Syntax
VOLATILE nitem [, nitem ...]
Description
If nitem names a common block, all members of the block are volatile. The volatile attribute of a variable is inherited by any direct or indirect equivalences, as shown in the example.
Example
COMMON /COM/ C1, C2
VOLATILE /COM/, DIR ! /COM/ and DIR are volatile
EQUIVALENCE (DIR, X) ! X is volatile
EQUIVALENCE (X, Y) ! Y is volatile
The WRITE statement is a data transfer output statement.
Syntax
WRITE ([unit=] u, format-identifier [,control-information) [iolist]
@ WRITE ([unit=] u, [NML=] namelist-group [,control-information])
Description
When a WRITE statement is executed the following operations are carried out: data is transferred to the standard output device from the items specified in the output list and format specification.[*] The data are transferred between the specified destinations in the order specified by the input/output list. Every item whose value is to be transferred must be defined.
Example
WRITE (6,90) NPAGE
90 FORMAT('1PAGE NUMBER ',I2,16X,'SALES REPORT, Cont.')
[*] if an asterisk (*) is used instead of a format identifier, the list-directed formatting rules apply.
[*] If an asterisk (*) is used instead of a format identifier, the list-directed formatting rules apply.
[*] if an asterisk (*) is used instead of a format identifier, the list-directed formatting rules apply.