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1.1 root 1: .so ../ADM/mac
2: .XX f77 311 "A Portable Fortran 77 Compiler"
3: .de XX
4: .IP "\f(CW\\$1\f1" 5
5: ..
6: .EQ
7: delim $$
8: .EN
9: . \".ND "1 August 1978"
10: .ND "30 June 1989"
11: .TL
12: A Portable Fortran 77 Compiler\(dg
13: .AU
14: S. I. Feldman
15: P. J. Weinberger
16: .AI
17: .MH
18: .AB
19: .PP
20: We report here on the first complete implementation of a compiler and run-time system for
21: the current Fortran language, known as Fortran 77.
22: The compiler is designed to be portable,
23: to be correct and complete,
24: and to generate code compatible with calling sequences produced by C compilers.
25: In particular, this Fortran is quite usable on
26: .UX
27: systems.
28: In this paper, we describe the language compiled,
29: interfaces between procedures,
30: and file formats assumed by the I/O system.
31: An appendix describes the Fortran 77 language.
32: .AE
33: .2C
34: .FS
35: \(dg This is a version of |reference(f77 v7man) revised by D. M. Gay.
36: .FE
37: .NH 1
38: Introduction
39: .PP
40: The current Fortran language, known as Fortran 77,
41: became an official American National Standard|reference(standard f77)
42: on April 3, 1978.
43: Fortran 77 supplants 1966 Standard Fortran|reference(standard f66).
44: We report here on a compiler and run-time system for Fortran 77.
45: The compiler and computation library were written by SIF, the I/O system by PJW.
46: We believe ours to be the first complete Fortran 77 system
47: to have been implemented.
48: This compiler is designed to be portable to a number of different machines,
49: to be correct and complete,
50: and to generate code compatible with calling sequences produced
51: by compilers for the C language|reference(cbook).
52: In particular,
53: it is in use on
54: .UX
55: systems.
56: The C compilers in use at Bell Labs include two families,
57: one based on D. M. Ritchie's PDP-11 compiler|reference(%type pamphlet
58: %author D. M. Ritchie
59: %title private communication), another
60: based on S. C. Johnson's portable C compiler|reference(pcc).
61: This Fortran compiler can drive the second passes of either family.
62: In this paper, we describe the language compiled,
63: interfaces between procedures,
64: and file formats assumed by the I/O system.
65: .PP
66: In the following text, Fortran keywords and other literal strings are written in
67: .CW "this font" .
68: .NH 2
69: Usage
70: .PP
71: .I F77
72: is a general-purpose command for compiling and loading Fortran and Fortran-related files.
73: The command to run the compiler is
74: .P1
75: f77 \fIflags file . . .\fR
76: .P2
77: EFL|reference(efl) and Ratfor|reference(ratfor)
78: source files will be preprocessed before
79: being presented to the Fortran compiler.
80: C and assembler source files will be compiled by the appropriate programs.
81: Object files will be loaded.
82: (The
83: .I f77
84: and
85: .I cc
86: commands cause slightly different loading sequences to be generated,
87: since Fortran programs need a few extra libraries and a different startup routine
88: than do C programs.)
89: The following file name suffixes are understood:
90: .TS
91: center;
92: aFCW a.
93: \&.f Fortran source file
94: \&.e EFL source file
95: \&.r Ratfor source file
96: \&.c C source file
97: \&.s Assembler source file
98: \&.o Object file
99: .TE
100: .Tm Options s
101: The following flags are understood:
102: .XX -S
103: Generate assembler output for each source file, but do not assemble it.
104: Assembler output for a source file
105: .CW x.f ,
106: .CW x.e ,
107: .CW x.r ,
108: or
109: .CW x.c
110: is put on file
111: .CW x.s .
112: .XX -c
113: Compile but do not load.
114: Output for
115: .CW x.f ,
116: .CW x.e ,
117: .CW x.r ,
118: .CW x.c ,
119: or
120: .CW x.s
121: is put on file
122: .CW x.o .
123: .XX -m
124: Apply the M4 macro preprocessor to each EFL or Ratfor source file before using the appropriate compiler.
125: .XX -p
126: Generate code to produce usage profiles.
127: .XX "-o \fIf\fR"
128: Put executable module on file
129: .I f.
130: (Default is
131: .CW a.out ).
132: .XX -w
133: Suppress all warning messages.
134: .XX -w66\
135: Suppress warnings about Fortran 66 features used.
136: .XX -O
137: Invoke the C object code optimizer.
138: .XX -C
139: Compile code that checks that subscripts are within array bounds.
140: .XX -onetrip\ \
141: Compile code that performs every
142: .CW do
143: loop at least once.
144: (See Section 2.11).
145: .XX -U
146: Do not convert upper case letters to lower case.
147: The default is to convert Fortran programs to lower case.
148: .XX -u
149: Make the default type of a variable
150: .CW undefined.
151: (See Section 2.2).
152: .XX -I2
153: On machines which support short integers,
154: make the default integer constants and variables short.
155: (\f(CW-I4\fR is the standard value of this option). (See Section 2.13).
156: All logical quantities will be short.
157: .XX -E
158: The remaining characters in the argument are used as an EFL flag argument.
159: .XX -R
160: The remaining characters in the argument are used as a Ratfor flag argument.
161: .XX -F
162: Ratfor and EFL source programs are pre-processed into Fortran files,
163: but those files are not compiled or removed.
164: .in -1i
165: .LP
166: Other flags,
167: all library names (arguments beginning \f(CW-l\fR),
168: and any names not ending with one of the understood suffixes are passed to the loader.
169: .NH 2
170: Implementation Strategy
171: .PP
172: The compiler and library are written entirely in C.
173: The compiler generates C compiler intermediate code.
174: Since there are C compilers running on a variety of machines,
175: relatively small changes will make this Fortran compiler generate code for any of them.
176: Furthermore, this approach guarantees that the resulting programs are compatible with C usage.
177: The runtime computational library is complete.
178: The mathematical functions rely on the functions in C's \fIlibm\fR.
179: The runtime I/O library makes use of D. M. Ritchie's Standard C I/O package
180: |reference(stdio)
181: for transferring data.
182: With the exception described below, only documented calls are used,
183: so it should be relatively easy to modify the I/O library
184: to run on other operating
185: systems.
186: .NH 1
187: Language Extensions
188: .PP
189: Fortran 77 includes almost all of Fortran 66 as a subset.
190: We describe the differences briefly in the Appendix.
191: The most important additions are a character string data type,
192: file-oriented input/output statements, and random access I/O.
193: Also, the language has been cleaned up considerably.
194: .PP
195: In addition to implementing the language specified in the Fortran 77 Standard,
196: our compiler implements a few extensions described in this section.
197: Most are useful additions to the language.
198: The remainder are extensions
199: to make it easier to communicate with C procedures
200: or to permit compilation of
201: old (1966 Standard) programs.
202: .NH 2
203: Double Complex Data Type
204: .PP
205: The new type
206: .CW "double complex"
207: is defined.
208: Each datum is represented by a pair of double precision real variables.
209: A double complex version of every
210: .CW complex
211: built-in function is provided.
212: The specific function names begin with \f(CWz\fR instead of \f(CWc\fR.
213: .NH 2
214: Implicit Undefined statement
215: .PP
216: Fortran 66 has a fixed rule that the type of a variable that does not appear in a type statement
217: is
218: .CW integer
219: if its first letter is one of
220: .CW ijklmn
221: and
222: .CW real
223: otherwise.
224: Fortran 77 has an
225: .CW implicit
226: statement for overriding this rule.
227: As an aid to good programming practice, we permit an additional type,
228: .CW undefined .
229: The statement
230: .P1
231: implicit undefined(a-z)
232: .P2
233: turns off the automatic data typing mechanism,
234: and the compiler will issue a diagnostic for each variable that is used but does
235: not appear in a type statement.
236: Specifying the
237: .CW -u
238: compiler flag is equivalent to beginning each procedure with this statement.
239: .NH 2
240: Recursion
241: .PP
242: Procedures may call themselves, directly or through a chain of other procedures.
243: .NH 2
244: Automatic Storage
245: .PP
246: Two new keywords are recognized,
247: .CW static
248: and
249: .CW automatic .
250: These keywords may appear as ``types'' in type statements and in
251: .CW implicit
252: statements.
253: Local variables are static by default;
254: there is exactly one copy of the datum, and its value is retained between calls.
255: There is one copy of each variable declared
256: .CW automatic
257: for each invocation of the procedure.
258: Automatic variables may not appear in
259: .CW equivalence ,
260: .CW data ,
261: or
262: .CW save
263: statements.
264: .NH 2
265: Source Input Format
266: .PP
267: The Standard expects input to the compiler to be in 72 column format:
268: except in comment lines,
269: the first five characters are the statement label, the next is the continuation character,
270: and the next sixty-six are the body of the line.
271: (If there are fewer than seventy-two characters on a line, the compiler pads it with blanks;
272: characters after the seventy-second are ignored).
273: .PP
274: To make typing Fortran programs easier,
275: our compiler also accepts input in variable length lines.
276: An ampersand
277: .CW &
278: in the first position of a line indicates a continuation
279: line; the remaining characters form the body of the line.
280: A tab character in one of the first six positions of a line signals the
281: end of the statement label and continuation part of the line;
282: the remaining characters form the body of the line.
283: A tab elsewhere on the line is treated as another kind of blank by the
284: compiler.
285: .PP
286: In the Standard, there are only 26 letters \(em Fortran is a one-case language.
287: Consistent with ordinary
288: .UX
289: system usage, our compiler expects lower case input.
290: By default, the compiler converts all upper case characters to lower case except those inside character constants.
291: However, if the
292: .CW -U
293: compiler flag is specified, upper case letters are not transformed.
294: In this mode, it is possible to specify external names with upper case letters in them,
295: and to have distinct variables differing only in case,
296: but then all Fortran keywords must be in lower case.
297: .NH 2
298: \f(CWinclude\fR Statement
299: .PP
300: The statement
301: .P1
302: include 'stuff'
303: .P2
304: is replaced by the contents of the file
305: .CW stuff .
306: .CW include s
307: may be nested to a reasonable depth, currently ten.
308: .NH 2
309: Binary Initialization Constants
310: .PP
311: A
312: .CW logical ,
313: .CW real ,
314: or
315: .CW integer
316: variable may be initialized in a
317: .CW data
318: statement
319: by a binary constant, denoted by a letter followed by a quoted string.
320: If the letter is
321: .CW b ,
322: the string is binary, and only zeros and ones are permitted.
323: If the letter is
324: .CW o ,
325: the string is octal, with digits
326: .CW 0-7 .
327: If the letter is
328: .CW z
329: or
330: .CW x ,
331: the string is hexadecimal, with digits
332: .CW 0-9a-f .
333: Thus, the statements
334: .P1
335: integer a(3)
336: data a / b'1010', o'12', z'a' /
337: .P2
338: initialize all three elements of
339: .I a
340: to ten.
341: .NH 2
342: Character Strings
343: .PP
344: For compatibility with C usage, the following backslash escapes are recognized:
345: .TS
346: center;
347: aFCW a.
348: \en newline
349: \et tab
350: \eb backspace
351: \ef form feed
352: \e0 null
353: \e' apostrophe (does not terminate a string)
354: \e" quotation mark (does not terminate a string)
355: \e\e \e
356: \e\fIx\fP \fIx\fR, where \fIx\fR is any other character
357: .TE
358: Fortran 77 only has one quoting character, the apostrophe.
359: Our compiler and I/O system recognize
360: both the apostrophe
361: .CW '
362: and the double-quote \f(CW"\fR.
363: If a string begins with one variety of quote mark, the other may be embedded within it
364: without using the repeated quote or backslash escapes.
365: .PP
366: Every unequivalenced scalar local character variable and every character string constant is aligned
367: on an
368: .CW integer
369: word boundary.
370: Each character string constant appearing outside a
371: .CW data
372: statement is followed by a
373: null character to ease communication with C routines.
374: .NH 2
375: Hollerith
376: .PP
377: Fortran 77 does not have the old Hollerith (\fIn\|\f(CWh\fR)
378: notation,
379: though the new Standard recommends implementing the old Hollerith feature
380: in order to improve compatibility with old programs.
381: In our compiler, Hollerith data may be used in place of character string constants,
382: and may also be used to initialize non-character variables in
383: .CW data
384: statements.
385: .NH 2
386: Equivalence Statements
387: .PP
388: As a very special and peculiar case,
389: Fortran 66 permits an element of a multiply-dimensioned array to be represented by
390: a singly-subscripted reference in
391: .CW equivalence
392: statements.
393: Fortran 77 does not permit this usage, since
394: subscript lower bounds may now be different from 1.
395: Our compiler permits single subscripts in
396: .CW equivalence
397: statements,
398: under the interpretation that all missing subscripts are equal to 1.
399: A warning message is printed for each such incomplete subscript.
400: .NH 2
401: One-Trip \f(CWdo\fP Loops
402: .PP
403: The Fortran 77 Standard requires that the range of a
404: .CW do
405: loop not be performed
406: if the initial value is already past the limit value,
407: as in
408: .P1
409: do 10 i = 2, 1
410: .P2
411: The 1966 Standard stated that the effect of such a statement was undefined,
412: but it was common practice that the range of a
413: .CW do
414: loop would be performed
415: at least once.
416: In order to accommodate old programs, though they were in violation of the 1966 Standard,
417: the
418: .CW -onetrip
419: compiler flag causes non-standard loops to be generated.
420: .NH 2
421: Commas in Formatted Input
422: .PP
423: The I/O system attempts to be more lenient than the
424: Standard when it seems worthwhile.
425: In a formatted read of non-character variables,
426: commas may be used as value separators in the input record,
427: overriding the field lengths given in the format statement.
428: Thus,
429: the format
430: .P1
431: (i10, f20.10, i4)
432: .P2
433: will read the record
434: .P1
435: -345,.05e-3,12
436: .P2
437: correctly.
438: .NH 2
439: Short Integers
440: .PP
441: On machines that support halfword integers,
442: the compiler accepts declarations of type
443: .CW integer\(**2 .
444: (Ordinary integers follow the Fortran rules about occupying the same
445: space as a
446: .CW real
447: variable; they are assumed to be of C type
448: .CW "long int" ;
449: halfword integers are of C type
450: .CW "short int" .)
451: An expression involving only objects of type
452: .CW integer\(**2
453: is of that type.
454: Generic functions return short or long integers depending on the actual types of their arguments.
455: If a procedure is compiled using the
456: .CW -I2
457: flag, all small integer constants will be
458: of type
459: .CW integer\(**2 .
460: If the precision of an integer-valued intrinsic function is not determined by the generic function rules,
461: one will be chosen that returns the prevailing length
462: (\f(CWinteger\(**2\fR when the \f(CW-I2\fR command flag is in effect).
463: When the
464: .CW -I2
465: option is in effect, all quantities of type
466: .CW logical
467: will be short.
468: Note that these short integer and logical quantities do not obey the standard rules for storage association.
469: .NH 2
470: Additional Intrinsic Functions
471: .PP
472: This compiler supports all of the intrinsic functions specified in the Fortran 77 Standard.
473: In addition, there are functions for performing bitwise Boolean operations
474: (\fIor\fR, \fIand\fR, \fIxor\fR, and \fInot\fR)
475: and for accessing the
476: .UX
477: command arguments
478: (\fIgetarg\fR and \fIiargc\fR).
479: .NH 1
480: Violations of the Standard
481: .PP
482: We know only two ways in which our Fortran system violates
483: the Fortran 77 standard:
484: .NH 2
485: Double Precision Alignment
486: .PP
487: The Fortran standards (both 1966 and 1977)
488: permit
489: .CW common
490: or
491: .CW equivalence
492: statements to force a double precision quantity onto an odd word boundary,
493: as in the following example:
494: .P1 I
495: real a(4)
496: double precision b,c
497: .sp .5
498: equivalence (a(1),b), (a(4),c)
499: .P2
500: Some machines (e.g., Honeywell 6000, IBM 360) require that double precision quantities be on double word boundaries;
501: other machines (e.g., IBM 370), run inefficiently if this alignment rule is not observed.
502: It is possible to tell which equivalenced and common variables suffer from a forced odd
503: alignment, but every double precision argument would have to be assumed on a bad boundary.
504: To load such a quantity on some machines,
505: it would be necessary to use separate operations to move the upper and lower halves
506: into the halves of an aligned temporary, then to load that double precision temporary; the reverse would be
507: needed to store a result.
508: We have chosen to require that all double precision real and complex quantities
509: fall on even word boundaries on machines with corresponding hardware requirements,
510: and to issue a diagnostic if the source code demands a violation of the rule.
511: .NH 2
512: \f(CWt\fR and \f(CWtl\fR Formats
513: .PP
514: The implementation of the
515: .CW t
516: (absolute tab)
517: and
518: .CW tl
519: (leftward tab)
520: format codes
521: is defective.
522: These codes allow rereading or rewriting part of the
523: record which has already been processed.
524: (See Section 6.3.2 in the Appendix.)
525: The implementation uses seeks,
526: so if the unit is not one which allows seeks,
527: such as a terminal,
528: the program is in error.
529: (People who can make a case for using
530: .CW tl
531: should let us know.)
532: A benefit of the implementation chosen is
533: that there is no upper limit on the length of
534: a record,
535: nor is it necessary to predeclare any record
536: lengths except where specifically required
537: by Fortran or the operating system.
538: .NH 1
539: Inter-Procedure Interface
540: .PP
541: To be able to write C procedures that call or are called by Fortran procedures,
542: it is necessary to know the conventions for procedure names,
543: data representation,
544: return values,
545: and argument lists that the compiled code obeys.
546: .NH 2
547: Procedure Names
548: .PP
549: On
550: .UX
551: systems,
552: the name of a common block or a Fortran procedure
553: has an underscore appended to it by the compiler
554: to distinguish it from a C procedure or external variable
555: with the same user-assigned name.
556: Fortran library procedure names have embedded underscores to avoid clashes
557: with user-assigned subroutine names.
558: .KF
559: .TS
560: center;
561: c c
562: l l.
563: Fortran C
564: .sp .5
565: integer\(**2 x short int x;
566: integer x long int x;
567: logical x long int x;
568: real x float x;
569: double precision x double x;
570: complex x struct { float r, i; } x;
571: double complex x struct { double dr, di; } x;
572: character\(**6 x char x[6];
573: .TE
574: .ce
575: \fBTable 1. Fortran and C declarations
576: .KE
577: .NH 2
578: Data Representations
579: .PP
580: Table 1 shows corresponding Fortran and C declarations:
581: (By the rules of Fortran,
582: .CW integer,
583: .CW logical,
584: and
585: .CW real
586: data occupy the same amount of memory).
587: .NH 2
588: Return Values
589: .PP
590: A function of type
591: .CW integer ,
592: .CW logical ,
593: .CW real ,
594: or
595: .CW "double precision"
596: must be declared as a C function that returns the corresponding type.
597: A
598: .CW complex
599: or
600: .CW "double complex"
601: function is equivalent to a C routine
602: with an additional
603: initial argument that points to the place where the return value is to be stored.
604: Thus,
605: .P1
606: complex function f( . . . )
607: .P2
608: is equivalent to
609: .P1
610: f_(temp, . . .)
611: struct { float r, i; } \(**temp;
612: . . .
613: .P2
614: A character-valued function is equivalent to a C routine with
615: two extra initial arguments:
616: a data address and a length.
617: Thus,
618: .P1
619: character\(**15 function g( . . . )
620: .P2
621: is equivalent to
622: .P1
623: g_(result, length, . . .)
624: char result[ ];
625: long int length;
626: . . .
627: .P2
628: and could be invoked in C by
629: .P1
630: char chars[15];
631: . . .
632: g_(chars, 15L, . . . );
633: .P2
634: Subroutines are invoked as if they were
635: .CW integer -valued
636: functions
637: whose value specifies which alternate return to use.
638: Alternate return arguments (statement labels) are not passed to the function,
639: but are used to do an indexed branch in the calling procedure.
640: (If the subroutine has no entry points with alternate return arguments,
641: the returned value is undefined.)
642: The statement
643: .P1
644: call nret(\(**1, \(**2, \(**3)
645: .P2
646: is treated exactly as if it were the computed
647: .CW goto
648: .P1
649: goto (1, 2, 3), nret( )
650: .P2
651: .NH 2
652: Argument Lists
653: .PP
654: All Fortran arguments are passed by address.
655: In addition,
656: for every non-function argument that is of type character,
657: an argument giving the length of the value is passed.
658: (The string lengths are
659: .CW "long int"
660: quantities passed by value).
661: The order of arguments is then:
662: extra arguments for complex and character functions,
663: address for each datum or function,
664: a \f(CWlong int\fR for each character argument (other than character-valued functions).
665: Thus, the call in
666: .P1
667: external f
668: character\(**7 s
669: integer b(3)
670: . . .
671: call sam(f, b(2), s)
672: .P2
673: is equivalent to that in
674: .P1
675: int f();
676: char s[7];
677: long int b[3];
678: . . .
679: sam_(f, &b[1], s, 7L);
680: .P2
681: Note that the first element of a C array always has subscript zero,
682: but Fortran arrays begin at 1 by default.
683: Fortran arrays are stored in column-major order, C arrays are stored in row-major order.
684: .NH 1
685: File Formats
686: .NH 2
687: Structure of Fortran Files
688: .PP
689: Fortran requires four kinds of external files:
690: sequential formatted and unformatted,
691: and direct formatted and unformatted.
692: On
693: .UX
694: systems,
695: these are all implemented as ordinary files
696: which are assumed to have the proper
697: internal structure.
698: .PP
699: Fortran I/O is based on ``records''.
700: When a direct file is opened in a Fortran program,
701: the record length of the records must be given,
702: and this is used by the Fortran I/O system to
703: make the file look as if it is made up of records
704: of the given length.
705: In the special case that the record length is given
706: as 1,
707: the files are not considered to be divided into records,
708: but are treated as byte-addressable byte strings;
709: that is,
710: as ordinary
711: .UX
712: file system files.
713: (A read or write request on such a file keeps consuming bytes until
714: satisfied, rather than being restricted to a single record.)
715: .PP
716: The peculiar requirements on sequential unformatted files
717: make it unlikely that they will ever be read or written by any means except Fortran I/O statements.
718: Each record is preceded and followed by
719: an integer containing the record's length in bytes.
720: .PP
721: The Fortran I/O system breaks sequential formatted files
722: into records while reading by using each newline
723: as a record separator.
724: The result of reading off the end of a record is undefined according to the Standard.
725: The I/O system is permissive and
726: treats the record as being extended by blanks.
727: On output,
728: the I/O system will write a newline at the end of each
729: record.
730: It is also possible for programs to write newlines
731: for themselves.
732: This is an error,
733: but the only effect will be that the single record
734: the user thought he wrote will be treated as
735: more than one record when being read or
736: backspaced over.
737: .NH 2
738: Portability Considerations
739: .PP
740: The Fortran I/O system uses only the facilities of the
741: standard C I/O library,
742: a widely available and fairly portable package,
743: with the following exceptions.
744: The I/O system needs to know whether a file
745: can be used for direct I/O,
746: and whether or not it is possible to backspace.
747: Both of these facilities are implemented
748: using the
749: .I fseek
750: routine,
751: so there is a routine
752: .I canseek
753: which determines if
754: .I fseek
755: will have the desired effect.
756: Combinations of the
757: \f(CWbackspace\fR, \f(CWwrite\fR, \f(CWendfile\fR, and
758: .CW close
759: statements may require that a file be shortened.
760: For efficiency, the \fIcopy\fR routine
761: that does this job uses the
762: .UX
763: system calls \fIcreat\fR, \fIread\fR, \fIwrite\fR, and \fIclose\fR.
764: Finally, to open write-only files, the I/O system must resort to the
765: \fIcreat\fR and \fIopen\fR system calls.
766: .NH 2
767: Pre-Connected Files and File Positions
768: .PP
769: Units 5, 6, and 0 are preconnected when the program starts.
770: Unit 5 is connected to the standard input,
771: unit 6 is connected to the standard output,
772: and unit 0 is connected to the standard error unit.
773: All are connected for sequential formatted I/O.
774: .PP
775: All the other units are also preconnected when execution
776: begins.
777: Unit
778: .I n
779: is connected to a file named \f(CWfort.\fIn\fR.
780: These files need not exist,
781: nor will they be created unless their units are used
782: without first executing an
783: .CW open .
784: The default connection is for sequential formatted I/O.
785: .PP
786: The Standard does not specify where a file which has been explicitly \f(CWopen\fRed
787: for sequential I/O is initially positioned.
788: Following common practice, the I/O system positions the file
789: at its beginning (and has done so for several years).
790: Originally it attempted to position the file
791: at the end, but this was a frequent source of confusion, and it
792: limited portability.
793: . \"In fact,
794: . \"the I/O system attempts to position the file at the end,
795: . \"so a
796: . \".B write
797: . \"will append to the file and a
798: . \".B read
799: . \"will result in an end-of-file indication.
800: . \"To position a file to its beginning,
801: . \"use a
802: . \".B rewind
803: . \"statement.
804: The preconnected units
805: 0, 5, and 6 are positioned as they come
806: from the program's parent process.
807: .NH
808: References
809: .LP
810: |reference_placement
811: .NH
812: Appendix. Differences Between Fortran 66 and Fortran 77
813: .PP
814: The following is a very brief description of the differences
815: between the 1966 and the 1977 Standard languages.
816: We assume that the reader is familiar with Fortran 66.
817: We do not pretend to be complete, precise,
818: or unbiased,
819: but plan to describe what we feel are the most important aspects of the new language.
820: .NH 0
821: Features Deleted from Fortran 66
822: .NH 2
823: Hollerith
824: .PP
825: All notions of ``Hollerith''
826: (\fIn\|\f(CWh\fR)
827: as data
828: have been officially removed, although our compiler, like almost all in the foreseeable future,
829: will continue to support this archaism.
830: .NH 2
831: Extended Range
832: .PP
833: In Fortran 66, under a set of very restrictive and rarely understood conditions, it is permissible
834: to jump out of the range of a
835: .CW do
836: loop, then jump back into it.
837: Extended range has been removed in the Fortran 77 language.
838: The restrictions are so special, and the implementation of extended range is so unreliable in many compilers,
839: that this change really counts as no loss.
840: .NH 1
841: Program Form
842: .NH 2
843: Blank Lines
844: .PP
845: Completely blank lines are now legal comment lines.
846: .NH 2
847: Program and Block Data Statements
848: .PP
849: A main program may now begin with a statement that gives that program an external name:
850: .P1
851: program work
852: .P2
853: Block data procedures may also have names.
854: .P1
855: block data stuff
856: .P2
857: There is now a rule that only
858: .I one
859: unnamed
860: block data procedure may appear in a program.
861: (This rule is not enforced by our system.)
862: The Standard does not specify the effect of the program and block data names,
863: but they are clearly intended to aid conventional loaders.
864: .NH 2
865: \f(CWentry\fP Statement
866: .PP
867: Multiple entry points are now legal.
868: Subroutine and function subprograms may have additional entry points,
869: declared by an
870: .CW entry
871: statement with an optional argument list.
872: .P1
873: entry extra(a, b, c)
874: .P2
875: Execution begins at the first statement following the
876: .CW entry
877: line.
878: All variable declarations must precede all executable statements in the procedure.
879: If the procedure begins with a
880: .CW subroutine
881: statement,
882: all entry points are subroutine names.
883: If it begins with a
884: .CW function
885: statement, each entry is a function entry point,
886: with type determined by the type declared for the entry name.
887: If any entry is a character-valued function,
888: then all entries must be.
889: In a function, an entry name of the same type as that where control entered
890: must be assigned a value.
891: Arguments do not retain their values between calls.
892: (The ancient trick of calling one entry point with a large number of arguments
893: to cause the procedure to ``remember'' the locations of those arguments,
894: then invoking an entry with just a few arguments for later calculation,
895: is still illegal.
896: Furthermore, the trick doesn't work in our implementation,
897: since arguments are not kept in static storage.)
898: .NH 2
899: \f(CWdo\fP Loops
900: .PP
901: .CW do
902: variables and range parameters may now be of integer, real, or double precision types.
903: (The use of floating point
904: .CW do
905: variables is very dangerous
906: because of the possibility of unexpected roundoff,
907: and we strongly recommend against their use).
908: The action of the
909: .CW do
910: statement is now defined for all values of the
911: .CW do
912: parameters.
913: The statement
914: .P1
915: do 10 i = l, u, d
916: .P2
917: performs one iteration if $l ~=~ u$ and
918: $ max (0^,^ left floor ( u - l ) / d^ right floor )$
919: iterations otherwise.
920: The
921: .CW do
922: variable has a predictable value when exiting a loop:
923: the value at the time a
924: .CW goto
925: or
926: .CW return
927: terminates the loop;
928: otherwise
929: the value that failed the limit test.
930: .NH 2
931: Alternate Returns
932: .PP
933: In a
934: .CW subroutine
935: or subroutine
936: .CW entry
937: statement,
938: some of the arguments may be noted by an asterisk, as in
939: .P1
940: subroutine s(a, \(**, b, \(**)
941: .P2
942: The meaning of the ``alternate returns'' is described in section 5.2 of the Appendix.
943: .NH 1
944: Declarations
945: .NH 2
946: \f(CWcharacter\fP Data Type
947: .PP
948: One of the biggest improvements to the language is the addition of a character-string data type.
949: Local and
950: common character variables must have a length denoted by a constant expression:
951: .P1
952: character\(**17 a, b(3,4)
953: character\(**(6+3) c
954: .P2
955: If the length is omitted entirely, it is assumed equal to 1.
956: A character string argument may have a constant length,
957: or the length may be declared to be the same as that of the corresponding actual argument at run time
958: by a statement like
959: .P1
960: character\(**(\(**) a
961: .P2
962: (There is an intrinsic function
963: .CW len
964: that returns the actual length of a character string).
965: Character arrays and common blocks containing character variables must be packed:
966: in an array of character variables, the first character of one element must follow the last character of
967: the preceding element, without holes.
968: .NH 2
969: \f(CWimplicit\fP Statement
970: .PP
971: The traditional implied declaration rules still hold:
972: a variable whose name begins with one of
973: .CW ijklmn
974: is of type
975: .CW integer .
976: Other variables are of type
977: .CW real
978: unless otherwise declared.
979: This general rule may be overridden with an
980: .CW implicit
981: statement:
982: .P1 0
983: implicit real(a-c,g), complex(w-z)
984: implicit character*(17) (s)
985: .P2
986: declares that variables whose name begins with one of
987: .CW abcg
988: are
989: .CW real ;
990: those beginning with
991: .CW wxyz
992: are assumed
993: .CW complex ,
994: and so on.
995: It is still poor practice to depend on implicit typing,
996: but this statement is an industry standard.
997: .NH 2
998: \f(CWparameter\fP Statement
999: .PP
1000: It is now possible to give a constant a symbolic name, as in
1001: .P1 0
1002: parameter (pi=3.1415d0,y=pi/3,s='hello')
1003: .P2
1004: The type of each parameter name is governed by the same implicit and explicit rules as for a variable.
1005: The right side of each equal sign must be a constant expression
1006: (an expression made up of constants, operators, and already defined parameters).
1007: .NH 2
1008: Array Declarations
1009: .PP
1010: Arrays may now have as many as seven dimensions.
1011: (Only three were permitted in 1966).
1012: The lower bound of each dimension may be declared
1013: to be other than 1 by
1014: using a colon.
1015: Furthermore, an adjustable array bound may be an integer expression involving constants,
1016: arguments, and variables in
1017: .CW common .
1018: .P1 0
1019: real a(-5:3, 7, m:n), b(n+1:2\(**n)
1020: .P2
1021: The upper bound on the last dimension of an array argument may be denoted by an asterisk
1022: to indicate that the upper bound is not specified:
1023: .P1 0
1024: integer a(5, \(**), b(\(**), c(0:1, -2:\(**)
1025: .P2
1026: .NH 2
1027: \f(CWsave\fP Statement
1028: .PP
1029: A poorly known rule of Fortran 66 is that local variables in a procedure do not necessarily retain their values between
1030: invocations of that procedure.
1031: At any instant in the execution of a program,
1032: if a common block is declared neither in the currently executing procedure
1033: nor in any of the procedures in the chain of callers,
1034: all of the variables in that common block also become undefined.
1035: (The only exceptions are variables that have been defined in a
1036: .CW data
1037: statement and never changed).
1038: These rules permit overlay and stack implementations for the affected variables.
1039: Fortran 77 permits one to specify that certain variables and common blocks are to retain their
1040: values between invocations.
1041: The declaration
1042: .P1
1043: save a, /b/, c
1044: .P2
1045: leaves the values of the variables
1046: .CW a
1047: and
1048: .CW c
1049: and all of the contents of common block
1050: .CW b
1051: unaffected by a return.
1052: The simple declaration
1053: .P1
1054: save
1055: .P2
1056: has this effect on all variables and common blocks in the procedure.
1057: A common block must be
1058: .CW save d
1059: in every procedure in which it is declared if the desired effect is to occur.
1060: .NH 2
1061: \f(CWintrinsic\fP Statement
1062: .PP
1063: All of the functions specified in the Standard
1064: are in the single category ``intrinsic functions'',
1065: rather than being divided into ``intrinsic'' and ``basic external'' functions.
1066: If an intrinsic function is to be passed to another procedure, it must be declared
1067: .CW intrinsic .
1068: Declaring it
1069: .CW external
1070: (as in Fortran 66) causes a function other than the built-in one to be passed.
1071: .........
1072: .NH 1
1073: Expressions
1074: .NH 2
1075: Character Constants
1076: .PP
1077: Character string constants are marked by strings surrounded by apostrophes.
1078: If an apostrophe is to be included in a constant, it is repeated:
1079: .P1
1080: 'abc'
1081: 'ain''t'
1082: .P2
1083: There are no null (zero-length) character strings in Fortran 77.
1084: Our compiler has two different quotation marks,
1085: .CW '
1086: and \f(CW"\fR.
1087: (See Section 2.8 in the main text.)
1088: .NH 2
1089: Concatenation
1090: .PP
1091: One new operator has been added, character string concatenation, marked by a double slash
1092: .CW // .
1093: The result of a concatenation is the string containing the characters of the left operand followed by the characters of
1094: the right operand.
1095: The strings
1096: .P1
1097: 'ab' // 'cd'
1098: 'abcd'
1099: .P2
1100: are equal.
1101: The strings being concatenated must be of constant length in all concatenations
1102: that are not the right sides of assignments.
1103: (The only concatenation expressions in which a
1104: character string declared adjustable with a
1105: .CW *(*)
1106: modifier
1107: or a substring denotation with nonconstant position values may appear
1108: are the right sides of assignments).
1109: .NH 2
1110: Character String Assignment
1111: .PP
1112: The left and right sides of a character assignment may not share storage.
1113: (The assumed implementation of character assignment is to copy characters from the right to the left side.)
1114: If the left side is longer than the right, it is padded with blanks.
1115: If the left side is shorter than the right, trailing characters are discarded.
1116: .NH 2
1117: Substrings
1118: .PP
1119: It is possible to extract a substring of a character variable or character array element, using the colon notation:
1120: .P1
1121: a(i,\|j) (m:n)
1122: .P2
1123: is the string of $(n-m+1)$ characters beginning at the
1124: $m sup th$ character of the character array element $a sub ij$.
1125: Results are undefined unless $m<=n$.
1126: Substrings may be used on the left sides of assignments and as procedure actual arguments.
1127: .NH 2
1128: Exponentiation
1129: .PP
1130: It is now permissible to raise real quantities to complex powers,
1131: or complex quantities to real or complex powers.
1132: (The principal part of the logarithm is used).
1133: Also, multiple exponentiation is now defined:
1134: .P1
1135: a\(**\(**b\(**\(**c = a \(**\(** (b\(**\(**c)
1136: .P2
1137: .NH 2
1138: Relaxation of Restrictions
1139: .PP
1140: Mixed mode expressions are now permitted.
1141: (For instance,
1142: it is permissible to combine integer and complex quantities in an expression.)
1143: .PP
1144: Constant expressions are permitted where a constant is allowed,
1145: except in
1146: .CW data
1147: statements.
1148: (A constant expression is made up of explicit constants and
1149: .CW parameter s
1150: and the Fortran operators,
1151: except for exponentiation to a floating-point power).
1152: An adjustable dimension may now be an integer expression involving constants,
1153: arguments, and variables in
1154: .CW common .
1155: .PP
1156: Subscripts may now be general integer expressions;
1157: the old
1158: $c v +- c'$
1159: rules have been removed.
1160: .CW do
1161: loop bounds may be general integer, real, or double precision expressions.
1162: Computed
1163: .CW goto
1164: expressions and I/O unit numbers may be general integer expressions.
1165: .NH 1
1166: Executable Statements
1167: .NH 2
1168: Block If
1169: .PP
1170: At last, an
1171: if-then-else
1172: branching structure (``Block If'') has been added to Fortran.
1173: A Block If begins with a statement of the form
1174: .P1
1175: if ( . . . ) then
1176: .P2
1177: and ends with an
1178: .P1
1179: end if
1180: .P2
1181: statement.
1182: Two other new statements may appear in a Block If.
1183: There may be several
1184: .P1
1185: else if(. . .) then
1186: .P2
1187: statements,
1188: followed by at most one
1189: .P1
1190: else
1191: .P2
1192: statement.
1193: If the logical expression in the Block If statement is true,
1194: the statements following it up to the
1195: next
1196: .CW elseif ,
1197: .CW else ,
1198: or
1199: .CW endif
1200: are executed.
1201: Otherwise, the next
1202: .CW elseif
1203: statement in the group is executed.
1204: If none of the
1205: .CW elseif
1206: conditions are true, control passes to the statements following the
1207: .CW else
1208: statement, if any.
1209: (The
1210: .CW else
1211: must follow all
1212: .CW elseif s
1213: in a Block If.
1214: Of course, there may be Block Ifs embedded inside of other Block If structures).
1215: A case construct may be rendered
1216: .P1
1217: if (s .eq. 'ab') then
1218: . . .
1219: else if (s .eq. 'cd') then
1220: . . .
1221: else
1222: . . .
1223: end if
1224: .P2
1225: .NH 2
1226: Alternate Returns
1227: .PP
1228: Some of the arguments of a subroutine call may be statement labels preceded by an asterisk, as in
1229: .P1
1230: call joe(j, \(**10, m, \(**2)
1231: .P2
1232: A
1233: .CW return
1234: statement may have an integer expression, such as
1235: .P1
1236: return k
1237: .P2
1238: If the entry point has
1239: $n$
1240: alternate return (asterisk) arguments
1241: and if $1<=k<=n$, the return is followed by a branch to the corresponding statement label;
1242: otherwise the usual return to the statement following the
1243: .CW call
1244: is executed.
1245: .NH 1
1246: Input/Output
1247: .NH 2
1248: Format Variables
1249: .PP
1250: A format may be the value of a character expression (constant or otherwise),
1251: or be stored in a character array, as in
1252: .P1
1253: write(6, '(i5)') x
1254: .P2
1255: .NH 2
1256: \f(CWend=\fP, \f(CWerr=\fP, and \f(CWiostat=\fP Clauses
1257: .PP
1258: A
1259: .CW read
1260: or
1261: .CW write
1262: statement may contain
1263: .CW end= ,
1264: .CW err= ,
1265: and
1266: .CW iostat=
1267: clauses, as in
1268: .P1 0
1269: write(6, 101, err=20, iostat=a(4))
1270: read(5, 101, err=20, end=30, iostat=x)
1271: .P2
1272: Here 5 and 6 are the
1273: .I unit s
1274: on which the I/O is done,
1275: 101 is the statement label of the associated format,
1276: 20 and 30 are statement labels,
1277: and
1278: .CW a
1279: and
1280: .CW x
1281: are integers.
1282: If an error occurs during I/O,
1283: control returns to the program at statement 20.
1284: If the end of the file is reached,
1285: control returns to the program at statement 30.
1286: In any case, the variable referred to in
1287: the
1288: .CW iostat=
1289: clause is given a value when
1290: the I/O statement finishes.
1291: (Yes, the value is assigned to the name on the right side of the equal sign.)
1292: This value is zero if all went well,
1293: negative for end of file,
1294: and some positive value for errors.
1295: .NH 2
1296: Formatted I/O
1297: .NH 3
1298: Character Constants
1299: .PP
1300: Character constants in formats are copied literally to the output.
1301: Character constants cannot be read into.
1302: .P1 0
1303: write(6,'(i2,'' isn''''t '',i1)') 7, 4
1304: .P2
1305: produces
1306: .P1
1307: 7 isn't 4
1308: .P2
1309: Here the format is the character constant
1310: .P1
1311: (i2,' isn''t ',i1)
1312: .P2
1313: and the character constant
1314: .P1
1315: isn't
1316: .P2
1317: is copied into the output.
1318: .NH 3
1319: Positional Editing Codes
1320: .PP
1321: .CW t ,
1322: .CW tl ,
1323: .CW tr ,
1324: and
1325: .CW x
1326: codes
1327: control where the
1328: next character is in the record.
1329: .CW tr\fIn
1330: or \fIn\f(CWx\fR
1331: specifies that the next character is
1332: $n$ to the right of the current position.
1333: .CW tl\fIn
1334: specifies that the next character is
1335: $n$ to the left of the current position,
1336: allowing parts of the record to be reconsidered.
1337: .CW t\fIn
1338: says that the next character is to be character
1339: number $n$ in the record.
1340: (See section 3.2 in the main text.)
1341: .NH 3
1342: Colon
1343: .PP
1344: A colon in the format terminates the I/O operation
1345: if there are no more data items in the I/O list;
1346: otherwise it has no effect.
1347: In the fragment
1348: .P1
1349: x='("hello", :, " there", i4)'
1350: write(6, x) 12
1351: write(6, x)
1352: .P2
1353: the first
1354: .CW write
1355: statement prints
1356: .CW "hello there 12" ,
1357: while the second only prints
1358: .CW hello .
1359: .NH 3
1360: Optional Plus Signs
1361: .PP
1362: According to the Standard,
1363: each implementation has the option of putting
1364: plus signs in front of non-negative
1365: numeric output.
1366: The
1367: .CW sp
1368: format code may be used to make the optional plus
1369: signs actually appear for all subsequent items
1370: while the format is active.
1371: The
1372: .CW ss
1373: format code guarantees that the I/O system will not
1374: insert the optional plus signs,
1375: and the
1376: .CW s
1377: format code restores the default behavior of
1378: the I/O system.
1379: (Since we never put out optional plus signs,
1380: .CW ss
1381: and
1382: .CW s
1383: codes have the same effect in our implementation.)
1384: .......
1385: .NH 3
1386: Blanks on Input
1387: .PP
1388: Blanks in numeric input fields,
1389: other than leading blanks
1390: will be ignored following a
1391: .CW bn
1392: code in a format
1393: statement,
1394: and will be treated as zeros following a
1395: .CW bz
1396: code in a format statement.
1397: The default for a unit may be changed by using
1398: the
1399: .CW open
1400: statement.
1401: (Blanks are ignored by default.)
1402: .NH 3
1403: Unrepresentable Values
1404: .PP
1405: The Standard requires that if a numeric item
1406: cannot be represented in the form required by a format code,
1407: the output field must be filled with asterisks.
1408: (We think this should have been an option.)
1409: .NH 3
1410: \f(CWI\fIw.m\fR Format
1411: .PP
1412: There is a new integer output code
1413: .CW i\fIw.m
1414: which is the same as
1415: .CW i\fIw ,
1416: except that there will be at least $m$
1417: digits in the output field,
1418: including,
1419: if necessary,
1420: leading zeros.
1421: The case
1422: .CW i\fIw\fP.0
1423: is special,
1424: in that if the value being printed is 0,
1425: the output field is
1426: entirely blank.
1427: .CW i\fIw\fP.1
1428: is the same as
1429: .CW i\fIw .
1430: .NH 3
1431: Floating Point
1432: .PP
1433: On input, exponents may start with one of
1434: .CW EeDd .
1435: All have the same meaning.
1436: On output we always use
1437: .CW E .
1438: The
1439: .CW e
1440: and
1441: .CW d
1442: format codes also have identical meanings.
1443: A leading zero before the decimal point in
1444: .CW e
1445: output
1446: without a scale factor is optional with the
1447: implementation.
1448: (We do not print it.)
1449: There is a
1450: .CW g\fIw.d
1451: format code which is the same as
1452: .CW e\fIw.d
1453: and
1454: .CW f\fIw.d
1455: on input,
1456: but which chooses
1457: .CW f
1458: or
1459: .CW e
1460: formats for output depending
1461: on the size of the number and of $d$.
1462: .NH 3
1463: \f(CWa\fP Format
1464: .PP
1465: \f(CWa\fP codes are used for character values.
1466: .CW a\fIw
1467: uses a field width of $w$,
1468: while a plain
1469: .CW a
1470: uses the length of the character item.
1471: .NH 2
1472: Standard Units
1473: .PP
1474: There are default formatted input and output units.
1475: The statement
1476: .P1
1477: read 10, a, b
1478: .P2
1479: reads from the standard unit using format statement 10.
1480: The default unit may be explicitly specified by an asterisk, as in
1481: .P1
1482: read(*, 10) a,b
1483: .P2
1484: Similarly, the standard output units is specified by a
1485: .CW print
1486: statement or an asterisk unit:
1487: .P1
1488: print 10
1489: write(*, 10)
1490: .P2
1491: .NH 2
1492: List-Directed Formatting
1493: .PP
1494: List-directed I/O is a
1495: kind of free format for sequential I/O.
1496: It is invoked by using an asterisk as the
1497: format identifier, as in
1498: .P1
1499: read(6, *) a,b,c
1500: .P2
1501: .PP
1502: On input,
1503: values are separated by strings of blanks
1504: and possibly a comma.
1505: Values,
1506: except for character strings,
1507: cannot contain blanks.
1508: End of record counts as a blank,
1509: except in character strings,
1510: where it is ignored.
1511: Complex constants are given as two real constants
1512: separated by a comma and enclosed in parentheses.
1513: A null input field,
1514: such as between two consecutive commas,
1515: means the corresponding variable in the
1516: I/O list is not changed.
1517: Values may be preceded by repetition counts,
1518: as in
1519: .P1
1520: 4*(3.,2.) 2*, 4*'hello'
1521: .P2
1522: which stands for 4 complex constants, 2 null values,
1523: and 4 string constants.
1524: .PP
1525: For output, suitable formats are chosen for
1526: each item.
1527: The values of character strings are printed;
1528: they are not enclosed in quotes, so they cannot be read back
1529: using list-directed input.
1530: .NH 2
1531: Direct I/O
1532: .PP
1533: A file connected for direct access consists of
1534: a set of equal-sized records each of which is
1535: uniquely identified by a positive integer.
1536: The records may be written or read in any order,
1537: using direct access I/O statements.
1538: .PP
1539: Direct access
1540: .CW read
1541: and
1542: .CW write
1543: statements
1544: have an extra argument,
1545: .CW rec=,
1546: which gives the record number to be read or written.
1547: .P1 0
1548: read(2, rec=13, err=20) (a(i), i=1, 203)
1549: .P2
1550: reads the thirteenth record into the array
1551: .CW a.
1552: .PP
1553: The size of the records must be given by an
1554: .CW open
1555: statement
1556: (see below).
1557: Direct access files may be connected for either formatted
1558: or unformatted I/O.
1559: .NH 2
1560: Internal Files
1561: .PP
1562: Internal files are character string objects,
1563: such as variables or substrings,
1564: or arrays of type character.
1565: In the former cases there is only a single record
1566: in the file;
1567: in the latter case each array element is a record.
1568: The Standard includes only sequential
1569: formatted I/O on internal files.
1570: (I/O is not a very precise term to use here,
1571: but internal files are dealt with using
1572: .CW read
1573: and
1574: .CW write ).
1575: There is no list-directed I/O on internal files.
1576: Internal files are used by giving the name of the
1577: character object in place of the unit number, as in
1578: .P1
1579: character\(**80 x
1580: read(5,"(a)") x
1581: read(x,"(i3,i4)") n1,n2
1582: .P2
1583: which reads a card image into
1584: .CW x
1585: and then reads
1586: two integers from the front of it.
1587: A sequential
1588: .CW read
1589: or
1590: .CW write
1591: always starts at the beginning
1592: of an internal file.
1593: .NH 2
1594: File Control Statements
1595: .PP
1596: These statements are used to connect and disconnect
1597: units and files,
1598: and to gather information about units and files.
1599: .NH 3
1600: \f(CWopen\fP Statement
1601: .PP
1602: The
1603: .CW open
1604: statement is used to connect a file with a
1605: unit,
1606: or to alter some properties of the connection.
1607: The following is a minimal example.
1608: .P1
1609: open(1, file='fort.junk')
1610: .P2
1611: .CW open
1612: takes a variety of arguments with meanings described below.
1613: .RS
1614: . \" macros here
1615: .EQ
1616: delim off
1617: .EN
1618: .de HP
1619: .RT
1620: .if !\\(IP .nr IP +1
1621: .sp \\n(PDu
1622: .ne 3v
1623: .in +\\n(PIu
1624: .ti -\\n(PIu
1625: \f(CW\\$1\fR\ \c
1626: ..
1627: .de TH
1628: .RT
1629: .sp \\n(PDu
1630: .ne 3v
1631: \f(CW\\$1\\$2\\$3\\$4\\$5\\$6\fR\ \c
1632: ..
1633: . \" end of macros
1634: .EQ
1635: delim $$
1636: .EN
1637: .HP unit=
1638: a small non-negative integer which is the unit to
1639: which the file is to be connected.
1640: We allow,
1641: at the time of this writing,
1642: 0 through 99.
1643: If this parameter is the first one in the
1644: .CW open
1645: statement,
1646: the
1647: .CW unit=
1648: can be omitted.
1649: .HP iostat=
1650: is the same as in
1651: .CW read
1652: or
1653: .CW write.
1654: .HP err=
1655: is the same as in
1656: .CW read
1657: or
1658: .CW write.
1659: .HP file=
1660: a character expression,
1661: which when stripped of trailing blanks,
1662: is the name of the file to be connected to the unit.
1663: The filename should not be given if the
1664: .CW status='scratch' .
1665: .HP status=
1666: one of
1667: .CW 'old' ,
1668: .CW 'new' ,
1669: .CW 'scratch' ,
1670: or
1671: .CW 'unknown' .
1672: If this parameter is not given,
1673: .CW 'unknown'
1674: is assumed.
1675: If
1676: .CW 'scratch'
1677: is given,
1678: a temporary file will be created.
1679: Temporary files are destroyed at the end of execution.
1680: If
1681: .CW 'new'
1682: is given,
1683: the file will be created if it doesn't exist,
1684: or truncated if it does.
1685: The meaning of
1686: .CW 'unknown'
1687: is processor dependent;
1688: our system complains if an
1689: .CW 'old'
1690: file does not exist,
1691: and creates a nonexistent file
1692: if it is
1693: .CW 'unknown' .
1694: .HP access=
1695: .CW 'sequential'
1696: or
1697: .CW 'direct' ,
1698: depending on whether the file is
1699: to be opened for sequential or direct I/O.
1700: .HP form=
1701: .CW 'formatted'
1702: or
1703: .CW 'unformatted' .
1704: .HP recl=
1705: a positive integer specifying the record length of
1706: the direct access file being opened.
1707: We measure all record lengths in bytes.
1708: On
1709: .UX
1710: systems a record length of 1 has the special meaning explained
1711: in section 5.1 of the text.
1712: .HP blank=
1713: .CW 'null'
1714: or
1715: .CW 'zero' .
1716: This parameter has meaning only for formatted I/O.
1717: The default value is
1718: .CW 'null' .
1719: .CW 'zero'
1720: means that blanks,
1721: other than leading blanks,
1722: in numeric input fields are to be treated as zeros.
1723: .RE
1724: .PP
1725: Opening a new file on a unit which is already connected
1726: has the effect of first closing the old file.
1727: .NH 3
1728: \f(CWclose\fP Statement
1729: .PP
1730: .CW close
1731: severs the connection between a unit and a file.
1732: The unit number must be given.
1733: The optional parameters are
1734: .CW iostat=
1735: and
1736: .CW err=
1737: with
1738: their usual meanings,
1739: and
1740: .CW status=
1741: either
1742: .CW 'keep'
1743: or
1744: .CW 'delete' .
1745: Scratch files cannot be kept,
1746: otherwise
1747: .CW 'keep'
1748: is the default.
1749: .CW 'delete'
1750: means the file will be removed.
1751: A simple example is
1752: .P1
1753: close(3, err=17)
1754: .P2
1755: .NH 3
1756: \f(CWinquire\fP Statement
1757: .PP
1758: The
1759: .CW inquire
1760: statement gives information about
1761: a unit
1762: (``inquire by unit'')
1763: or a file (``inquire by file'').
1764: Simple examples are:
1765: .P1 0
1766: inquire(unit=3, name=x)
1767: inquire(file='junk', number=n, exist=l)
1768: .P2
1769: .RS
1770: .HP file=
1771: a character variable specifies the file the
1772: .CW inquire
1773: is about.
1774: Trailing blanks in the file name are ignored.
1775: .HP unit=
1776: an integer variable specifies the unit the
1777: .CW inquire
1778: is about.
1779: Exactly one of
1780: .CW file=
1781: or
1782: .CW unit=
1783: must be used.
1784: .HP "iostat=, err="
1785: are as before.
1786: .HP exist=
1787: a logical variable.
1788: The logical variable is set to \f(CW.true.\fP if the file or unit
1789: exists and is set to \f(CW.false.\fP otherwise.
1790: .HP opened=
1791: a logical variable.
1792: The logical variable is set to \f(CW.true.\fP if the file
1793: is connected to a unit or if the unit is connected
1794: to a file,
1795: and it is set to \f(CW.false.\fP otherwise.
1796: .HP number=
1797: an integer variable to which is assigned the
1798: number of the unit connected to the file,
1799: if any.
1800: .HP named=
1801: a logical variable to which is assigned \f(CW.true.\fP if the file has a name,
1802: or \f(CW.false.\fP otherwise.
1803: .HP name=
1804: a character variable to which is assigned the name
1805: of the file (inquire by file) or, if known, the name of the
1806: file connected to the unit (inquire by unit).
1807: .HP access=
1808: a character variable to which will be assigned
1809: the value
1810: .CW 'sequential'
1811: if the connection is for
1812: sequential I/O,
1813: .CW 'direct'
1814: if the connection is for direct I/O.
1815: The value becomes undefined if there is no connection.
1816: .HP sequential=
1817: a character variable to which is assigned the
1818: value
1819: .CW 'yes'
1820: if the file could be connected for
1821: sequential I/O,
1822: .CW 'no'
1823: if the file could not be connected for sequential I/O,
1824: and
1825: .CW 'unknown'
1826: if we can't tell.
1827: .HP direct=
1828: a character variable to which is assigned the value
1829: .CW 'yes'
1830: if the file could be connected for direct I/O,
1831: .CW'no'
1832: if the file could not be connected for direct
1833: I/O,
1834: and
1835: .CW 'unknown'
1836: if we can't tell.
1837: .HP form=
1838: a character variable to which is assigned the value
1839: .CW 'formatted'
1840: if the file is connected for formatted I/O,
1841: or
1842: .CW 'unformatted'
1843: if the file is connected for unformatted
1844: I/O.
1845: .HP formatted=
1846: a character variable to which is assigned the value
1847: .CW 'yes'
1848: if the file could be connected for formatted I/O,
1849: .CW 'no'
1850: if the file could not be connected for formatted I/O,
1851: and
1852: .CW 'unknown'
1853: if we can't tell.
1854: .HP unformatted=
1855: a character variable to which is assigned the value
1856: .CW 'yes'
1857: if
1858: the file could be connected for unformatted I/O,
1859: .CW 'no'
1860: if the file could not be connected for unformatted I/O,
1861: and
1862: .CW 'unknown'
1863: if we can't tell.
1864: .HP recl=
1865: an integer variable to which is assigned the record length
1866: of the records in the file if the file is connected
1867: for direct access.
1868: .HP nextrec=
1869: an integer variable to which is assigned one more
1870: than the number of the last record read from a file connected
1871: for direct access.
1872: .HP blank=
1873: a character variable to which is assigned the value
1874: .CW 'null'
1875: if null blank control is in effect for the file
1876: connected for formatted I/O,
1877: .CW 'zero'
1878: if blanks are being converted to zeros and
1879: the file is connected for formatted I/O.
1880: .RE
1881: .PP
1882: The gentle reader
1883: will remember that the people who wrote the standard
1884: probably weren't thinking of his needs.
1885: Here is an example.
1886: The declarations are omitted.
1887: .P1
1888: open(1, file="/dev/console")
1889: .P2
1890: On a
1891: .UX
1892: system this statement opens the console for formatted sequential
1893: I/O.
1894: An
1895: .CW inquire
1896: statement for either unit 1 or file
1897: .CW "/dev/console"
1898: would reveal that the file exists, is connected to unit 1,
1899: has a name, namely
1900: .CW "/dev/console" ,
1901: is opened for sequential I/O,
1902: could be connected for sequential I/O,
1903: could not be connected for direct I/O (can't seek),
1904: is connected for formatted I/O,
1905: could be connected for formatted I/O,
1906: could not be connected for unformatted I/O
1907: (can't seek),
1908: has neither a record length nor a next record number,
1909: and is ignoring blanks in numeric fields.
1910: .PP
1911: In the
1912: .UX
1913: system environment,
1914: the only way to discover what permissions you have
1915: for a file is to open it and try to read and write it.
1916: The
1917: .CW iostat=
1918: parameter will return system error numbers.
1919: The
1920: .CW inquire
1921: statement does not give a way of determining permissions.
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