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Annotation of 43BSDTahoe/new/help/src/f77/io_details, revision 1.1

1.1     ! root        1: .      \" this is the same as /usr/doc/f77/f77IO.ms, 4.3 version
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        !            40: \\*(SN
        !            41: ..
        !            42: .de Fo
        !            43: Fortran\\$1
        !            44: ..
        !            45: .TI F77/IO_DETAILS "June 15, 1985"
        !            46: Introduction to the f77 I/O Library
        !            47: .na
        !            48: .ce
        !            49: David L. Wasley
        !            50: .PP
        !            51: The f77 I/O library, libI77.a,
        !            52: includes routines to perform all of the standard types of
        !            53: .Fo
        !            54: input and output.
        !            55: Several enhancements and extensions to
        !            56: .Fo
        !            57: I/O have been added.
        !            58: The f77 library routines use the C stdio library routines to provide
        !            59: efficient buffering for file I/O.
        !            60: .sp 1
        !            61: .Nh 1 "Fortran I/O"
        !            62: The requirements of the
        !            63: .Sm ANSI
        !            64: standard impose significant overhead
        !            65: on programs that do large amounts of I/O. Formatted I/O can be
        !            66: very ``expensive'' while direct access binary I/O is usually very efficient.
        !            67: Because of the complexity of
        !            68: .Fo
        !            69: I/O,
        !            70: some general concepts deserve clarification.
        !            71: .Nh 2 "Types of I/O"
        !            72: There are three forms of I/O:
        !            73: .B formatted ,
        !            74: .B unformatted ,
        !            75: and
        !            76: .B list-directed .
        !            77: The last is
        !            78: related to formatted but does not obey all the rules for formatted I/O.
        !            79: There are two modes of access to
        !            80: .B external
        !            81: and
        !            82: .B internal
        !            83: files:
        !            84: .B direct
        !            85: and
        !            86: .B sequential .
        !            87: The definition of a logical record depends upon the
        !            88: combination of I/O form and mode specified by the
        !            89: .Fo
        !            90: I/O statement.
        !            91: .Nh 3 "Direct access"
        !            92: A logical record in a
        !            93: .B direct
        !            94: access
        !            95: .B external
        !            96: file is a string of bytes
        !            97: of a length specified when the file is opened.
        !            98: Read and write statements must not specify logical records longer than
        !            99: the original record size definition. Shorter logical records are allowed.
        !           100: .B Unformatted
        !           101: direct writes leave the unfilled part of the record undefined.
        !           102: .B Formatted
        !           103: direct writes cause the unfilled record to be padded with blanks.
        !           104: .Nh 3 "Sequential access"
        !           105: Logical records in
        !           106: .B sequentially
        !           107: accessed
        !           108: .B external
        !           109: files may be of arbitrary
        !           110: and variable length.
        !           111: Logical record length for
        !           112: .B unformatted
        !           113: sequential files is determined by
        !           114: the size of items in the iolist.
        !           115: The requirements of this form of I/O cause the external physical
        !           116: record size to be somewhat larger than the logical record size.
        !           117: For
        !           118: .B formatted
        !           119: write statements, logical record length is determined by
        !           120: the format statement interacting with the iolist at execution time.
        !           121: The ``newline'' character is the logical record delimiter.
        !           122: Formatted sequential access causes one or more logical records
        !           123: ending with ``newline'' characters to be read or written.
        !           124: .Nh 3 "List directed I/O"
        !           125: Logical record length for
        !           126: .B list-directed
        !           127: I/O is relatively meaningless.
        !           128: On output, the record length is dependent on the magnitude of the
        !           129: data items.
        !           130: On input, the record length is determined by the data types and the file
        !           131: contents.
        !           132: By ANSI definition, a slash, ``/'', terminates execution of a
        !           133: list-directed input operation.
        !           134: .Nh 3 "Internal I/O"
        !           135: The logical record length for an
        !           136: .B internal
        !           137: read or write is the length of the
        !           138: character variable or array element. Thus a simple character variable
        !           139: is a single logical record. A character variable array is similar to
        !           140: a fixed length direct access file, and obeys the same rules.
        !           141: .B Unformatted
        !           142: I/O is not allowed on "internal" files.
        !           143: .Nh 2 "I/O execution"
        !           144: Note that each execution of a
        !           145: .Fo
        !           146: .B unformatted
        !           147: I/O statement causes a single
        !           148: logical record to be read or written. Each execution of a
        !           149: .Fo
        !           150: .B formatted
        !           151: I/O statement causes one or more logical records to be read or written.
        !           152: .PP
        !           153: A slash, ``/'', will terminate assignment of
        !           154: values to the input list during
        !           155: .B list-directed
        !           156: input and the remainder of the current input line is skipped.
        !           157: The standard is rather vague on this point but seems to require that
        !           158: a new external logical record be found at the start of any formatted
        !           159: input. Therefore data following the slash is ignored and may be used
        !           160: to comment the data file.
        !           161: .PP
        !           162: .B "Direct access list-directed"
        !           163: I/O is not allowed.
        !           164: .B "Unformatted internal"
        !           165: I/O is not allowed.
        !           166: Both the above will be caught by the compiler.
        !           167: All other flavors of I/O are allowed, although some are not part of the
        !           168: .Sm ANSI
        !           169: standard.
        !           170: .PP
        !           171: Any I/O statement may include an
        !           172: .B err=
        !           173: clause to specify an alternative branch to be taken on errors
        !           174: and/or an
        !           175: .B iostat=
        !           176: clause to return the specific error code.
        !           177: Any error detected during I/O processing will cause the program to abort
        !           178: unless either
        !           179: .B err=
        !           180: or
        !           181: .B iostat=
        !           182: has been specificed in the program.
        !           183: Read statements may include
        !           184: .B end=
        !           185: to branch on end-of-file.
        !           186: The end-of-file indication for that logical unit may be reset with a
        !           187: .B backspace
        !           188: statement.
        !           189: File position and the value of I/O list items is undefined following an error.
        !           190: .sp 1
        !           191: .Nh 1 "Implementation details"
        !           192: Some details of the current implementation may be useful in understanding
        !           193: constraints on
        !           194: .Fo
        !           195: I/O.
        !           196: .Nh 2 "Number of logical units"
        !           197: Unit numbers must be in the range 0 \- 99.
        !           198: The maximum number of logical units that a program may have open at one
        !           199: time is the same as the
        !           200: .UX
        !           201: system limit, currently 48.
        !           202: .Nh 2 "Standard logical units"
        !           203: By default, logical units 0, 5, and 6
        !           204: are opened to ``stderr'', ``stdin'', and ``stdout'' respectively.
        !           205: However they can be re-defined with an 
        !           206: .B open
        !           207: statement.
        !           208: To preserve error reporting, it is an error to close logical unit 0
        !           209: although it may be reopened to another file.
        !           210: .PP
        !           211: If you want to open the default file name for any preconnected logical unit,
        !           212: remember to 
        !           213: .B close
        !           214: the unit first.
        !           215: Redefining the standard units may impair normal console I/O.
        !           216: An alternative is to
        !           217: use shell re-direction to externally re-define the above units.
        !           218: To re-define default blank control or format of the standard input or output
        !           219: files, use the 
        !           220: .B open
        !           221: statement specifying the unit number and no
        !           222: file name (see section 2.4).
        !           223: .PP
        !           224: The standard units, 0, 5, and 6, are named internally ``stderr'', ``stdin'',
        !           225: and ``stdout'' respectively.
        !           226: These are not actual file names and can not be used for opening these units.
        !           227: .B Inquire
        !           228: will not return these names and will indicate
        !           229: that the above units are not named unless they have been opened to real files.
        !           230: The names are meant to make error reporting more meaningful.
        !           231: .Nh 2 "Vertical format control"
        !           232: Simple vertical format control is implemented. The logical unit must be opened
        !           233: for sequential access with "form = 'print'"
        !           234: (see section 3.2).
        !           235: Control codes ``0'' and ``1'' are replaced in the output file
        !           236: with ``\\n'' and ``\\f'' respectively.
        !           237: The control character ``+'' is not implemented and, like
        !           238: any other character in the first position of a record
        !           239: written to a ``print'' file, is dropped.
        !           240: .PP
        !           241: An alternative is to use
        !           242: the filter 'fpr'(1) for vertical format control.
        !           243: It replaces ``0'' and ``1'' by
        !           244: ``\\n'' and ``\\f'' respectively, and implements the ``+'' control code.
        !           245: Unlike "form = 'print'"
        !           246: which drops unrecognized form control characters, 'fpr' copies those
        !           247: characters to the output file.
        !           248: .PP
        !           249: No vertical format control is recognized for
        !           250: .B "direct formatted"
        !           251: output or
        !           252: .B "list directed"
        !           253: output.
        !           254: .Nh 2 "File names and the open statement"
        !           255: A file name may be specified in an
        !           256: .B open
        !           257: statement for the
        !           258: logical unit.
        !           259: If a logical unit is opened by an
        !           260: .B open
        !           261: statement which does
        !           262: not specify a file name, or it is opened implicitly by the execution
        !           263: of a
        !           264: .B read ,
        !           265: .B write ,
        !           266: .B backspace
        !           267: or
        !           268: .B rewind
        !           269: statement, then the default file name is ``fort.N'' where N is
        !           270: the logical unit number.
        !           271: Before opening the file, the library checks for an environment
        !           272: variable with a name identical to the tail of the
        !           273: file name with periods removed.
        !           274: If it finds such an environment variable, it uses its value
        !           275: as the actual name of the file.
        !           276: For example, a program containing:
        !           277: .nf
        !           278: 
        !           279:      open(32,file="/usr/guest/census/data.d")
        !           280:      read(32,100) vec
        !           281:      write(44) vec
        !           282: 
        !           283: .fi
        !           284: normally will read from '/usr/guest/census/data.d' and write to
        !           285: .B fort.44
        !           286: in the current directory.
        !           287: If the environment variables 'datad' and 'fort44' are set,
        !           288: e.g.:
        !           289: .nf
        !           290: 
        !           291:    % setenv datad mydata
        !           292:    % setenv fort44 myout
        !           293: 
        !           294: .fi
        !           295: in the C shell or:
        !           296: .nf
        !           297: 
        !           298:    $ datad=mydata
        !           299:    $ fort44=myout
        !           300:    $ export datad fort44
        !           301: 
        !           302: .fi
        !           303: in the Bourne shell, then the program will read from 'mydata' and
        !           304: write to 'myout'.
        !           305: .PP
        !           306: An
        !           307: .B open
        !           308: statement need not specify a file name. If it refers to a logical
        !           309: unit that is already open, the 
        !           310: .B blank=
        !           311: and 
        !           312: .B form=
        !           313: specifiers may be
        !           314: redefined without affecting the current file position.
        !           315: Otherwise, if 'status = "scratch"'
        !           316: is specified, a temporary file with a
        !           317: name of the form ``tmp.FXXXXXX'' will be opened,
        !           318: and, by default, will be deleted when closed or during
        !           319: termination of program execution.
        !           320: .PP
        !           321: It is an error to try to open an existing file with 'status = "new"'.
        !           322: It is an error to try to open a nonexistent file with 'status = "old"'.
        !           323: By default, 'status = "unknown"'
        !           324: will be assumed, and a file will be created if necessary.
        !           325: .PP
        !           326: By default, files are positioned
        !           327: at their beginning upon opening, but see 'fseek'(3f)
        !           328: and 'ioinit'(3f) for alternatives.
        !           329: Existing files are never truncated on opening.
        !           330: Sequentially accessed external files are truncated to the current file
        !           331: position on
        !           332: .B close ,
        !           333: .B backspace
        !           334: , or
        !           335: .B rewind
        !           336: only if the last
        !           337: access to the file was a write.
        !           338: An
        !           339: .B endfile
        !           340: always causes such files to be truncated to the current
        !           341: file position.
        !           342: .Nh 2 "Format interpretation"
        !           343: Formats which are in format statements are parsed by the compiler;
        !           344: formats in
        !           345: .B read ,
        !           346: .B write
        !           347: , and
        !           348: .B print
        !           349: statements
        !           350: are parsed during execution by the
        !           351: .Sm I/O
        !           352: library.
        !           353: Upper as well as lower case characters are recognized in format statements
        !           354: and all the alphabetic arguments to the I/O library routines.
        !           355: .PP
        !           356: If the external representation of a datum
        !           357: is too large for the field width specified, the specified
        !           358: field is filled with asterisks (\(**).
        !           359: On
        !           360: .B Ew.dEe
        !           361: output,
        !           362: the exponent field will be filled with asterisks if the
        !           363: exponent representation is too large.
        !           364: This will only happen if ``e'' is zero.
        !           365: .PP
        !           366: On output, a real value that is truly zero will display as ``0.'' to
        !           367: distinguish it from a very small non-zero value.
        !           368: If this causes problems for other input systems, the
        !           369: .B BZ
        !           370: edit descriptor may be used to cause the field
        !           371: following the decimal point to be filled with zero's.
        !           372: .PP
        !           373: Non-destructive tabbing is implemented for both internal and external
        !           374: formatted I/O.
        !           375: Tabbing left or right on output
        !           376: does not affect previously written portions of a record.
        !           377: Tabbing right on output
        !           378: causes unwritten portions of a record to be filled with blanks.
        !           379: Tabbing right off the end of an input logical record is an error.
        !           380: Tabbing left beyond the beginning of an input logical record leaves
        !           381: the input pointer at the beginning of the record.
        !           382: The format specifier
        !           383: .B T
        !           384: must be followed by a positive non-zero number.
        !           385: If it is not, it will have a different meaning (see section 3.1).
        !           386: .PP
        !           387: Tabbing left requires seek ability on the logical unit.
        !           388: Therefore it is not allowed in I/O to a terminal or pipe.
        !           389: Likewise, nondestructive tabbing in either direction is possible
        !           390: only on a unit that can seek. Otherwise tabbing right or spacing with
        !           391: .B X
        !           392: will write blanks on the output.
        !           393: .Nh 2 "List directed output"
        !           394: In formatting list directed output, the I/O system tries to prevent
        !           395: output lines longer than 80 characters.
        !           396: Each external datum will be separated by two spaces.
        !           397: List-directed output of
        !           398: .B complex
        !           399: values includes an appropriate comma.
        !           400: List-directed output distinguishes between
        !           401: .B real
        !           402: and
        !           403: .B "double precision"
        !           404: values and formats them differently.
        !           405: Output of a character string that includes ``\\n''
        !           406: is interpreted reasonably by the output system.
        !           407: .Nh 2 "I/O errors"
        !           408: If I/O errors are not trapped by the user's program an appropriate
        !           409: error message will be written to ``stderr'' before aborting.
        !           410: An error number will be printed in ``[ ]'' along with a brief error message
        !           411: showing the logical unit and I/O state.
        !           412: Error numbers < 100 refer to
        !           413: .UX
        !           414: errors, and are described in the
        !           415: introduction to chapter 2 of the
        !           416: .UX
        !           417: Programmer's Manual.
        !           418: Error numbers \(>= 100 come from the I/O library, and are described
        !           419: on-line in "help f77 io_err_msgs".
        !           420: For internal I/O, part of the string will be printed with ``|'' at the
        !           421: current position in the string.
        !           422: For external I/O, part of the current record will be displayed if
        !           423: the error was caused during reading from a file that can backspace.
        !           424: .sp 1
        !           425: .Nh 1 "Non-``ANSI Standard'' extensions"
        !           426: Several extensions have been added to the I/O system to provide
        !           427: for functions omitted or poorly defined in the standard.
        !           428: Programmers should be aware that these are non-portable.
        !           429: .Nh 2 "Format specifiers"
        !           430: .B B
        !           431: is an acceptable edit control specifier. It causes return to the
        !           432: default mode of blank interpretation.
        !           433: This is consistent with
        !           434: .B S
        !           435: which returns to default sign control.
        !           436: .PP
        !           437: .B P
        !           438: by itself is equivalent to
        !           439: .B 0P .
        !           440: It resets the scale factor to the
        !           441: default value, 0.
        !           442: .PP
        !           443: The form of the
        !           444: .B Ew.dEe
        !           445: format specifier has been extended to
        !           446: .B D
        !           447: also.
        !           448: The form
        !           449: .B Ew.d.e
        !           450: is allowed but is not standard.
        !           451: The ``e'' field specifies the minimum number of digits or spaces in the
        !           452: exponent field on output.
        !           453: If the value of the exponent is too large, the exponent notation
        !           454: .B e
        !           455: or
        !           456: .B d
        !           457: will be dropped from the output to allow one
        !           458: more character position.
        !           459: If this is still not adequate, the ``e'' field will be filled with
        !           460: asterisks (\(**).
        !           461: The default value for ``e'' is 2.
        !           462: .PP
        !           463: An additional form of tab control specification has been added.
        !           464: The
        !           465: .Sm ANSI
        !           466: standard forms 'TRn', 'TLn', and 'Tn' are supported
        !           467: where 'n'
        !           468: is a positive non-zero number.
        !           469: If 'T' or 'nT' is specified, tabbing will
        !           470: be to the next (or n-th) 8-column tab stop.
        !           471: Thus columns of alphanumerics can be lined up without counting.
        !           472: .PP
        !           473: A format control specifier has been added to suppress the newline
        !           474: at the end of the last record of a formatted sequential write. The
        !           475: specifier is a dollar sign ($). It is constrained by the same rules
        !           476: as the colon (:). It is used typically for console prompts.
        !           477: For example:
        !           478: .nf
        !           479: 
        !           480:       write (\(**, "(\(fmenter value for x: \(fm,$)")
        !           481:       read (\(**,\(**) x
        !           482: .fi
        !           483: .PP
        !           484: Radices other than 10 can be specified for formatted integer I/O
        !           485: conversion. The specifier is patterned after
        !           486: .B P ,
        !           487: the scale factor for
        !           488: floating point conversion. It remains in effect until another radix is
        !           489: specified or format interpretation is complete. The specifier is defined
        !           490: as '[n]R' where 2 \(<= n \(<= 36. If
        !           491: .I n
        !           492: is omitted,
        !           493: the default decimal radix is restored.
        !           494: .PP
        !           495: The format specifier 'Om.n' may be used for an octal conversion;
        !           496: it is equivalent to '8R,Im.n,10R'.
        !           497: Similarly, 'Zm.n' is equivalent to '16R,Im.n,10R' and
        !           498: may be used for an hexadecimal conversion;
        !           499: .PP
        !           500: In conjunction with the above, a sign control specifier has been added
        !           501: to cause integer values to be interpreted as unsigned during output
        !           502: conversion. The specifier is
        !           503: .B SU
        !           504: and remains in effect until another
        !           505: sign control specifier is encountered, or format interpretation is
        !           506: complete.
        !           507: Radix and ``unsigned'' specifiers could be used to format
        !           508: a hexadecimal dump, as follows:
        !           509: 
        !           510: .nf
        !           511: 2000  format ( SU, 8Z10.8 )
        !           512: .fi
        !           513: 
        !           514: (Note: Unsigned integer values greater than (2\(**\(**31 - 1),
        !           515: can be read and written using \fBSU\fP.
        !           516: However they can not be used in
        !           517: computations because
        !           518: .Fo
        !           519: uses signed arithmetic and such values appear to the arithmetic unit
        !           520: as negative numbers.)
        !           521: .Nh 2 "Print files"
        !           522: The
        !           523: .Sm ANSI
        !           524: standard is ambiguous regarding the definition of a ``print'' file.
        !           525: Since
        !           526: .UX
        !           527: has no default ``print'' file, an additional
        !           528: .B form=
        !           529: specifier
        !           530: is now recognized in the
        !           531: .B open
        !           532: statement.
        !           533: Specifying
        !           534: .B "form = \(fmprint\(fm"
        !           535: implies
        !           536: .B formatted
        !           537: and enables vertical format
        !           538: control for that logical unit (see section 2.3).
        !           539: Vertical format control is interpreted only on sequential formatted writes
        !           540: to a ``print'' file.
        !           541: .PP
        !           542: The
        !           543: .B inquire
        !           544: statement will return
        !           545: .B print
        !           546: in the
        !           547: .B form=
        !           548: string variable
        !           549: for logical units opened as ``print'' files.
        !           550: It will return -1 for the unit number of an unconnected file.
        !           551: .PP
        !           552: If a logical unit is already open, an
        !           553: .B open
        !           554: statement including the
        !           555: .B form=
        !           556: option or the
        !           557: .B blank=
        !           558: option will do nothing but re-define those options.
        !           559: This instance of the
        !           560: .B open
        !           561: statement need not include the file name, and
        !           562: must not include a file name if
        !           563: .B unit=
        !           564: refers to a standard input or output.
        !           565: Therefore, to re-define the standard output as a ``print'' file, use:
        !           566: .nf
        !           567: 
        !           568:       open (unit=6, form=\(fmprint\(fm)
        !           569: .fi
        !           570: .Nh 2 "Scratch files"
        !           571: A
        !           572: .B close
        !           573: statement with 'status = "keep"'
        !           574: may be specified for temporary files.
        !           575: This is the default for all other files.
        !           576: Remember to get the scratch file's real name,
        !           577: using
        !           578: .B inquire ,
        !           579: if you want to re-open it later.
        !           580: .Nh 2 "List directed I/O"
        !           581: List directed read has been modified to allow
        !           582: tab characters wherever blanks are allowed.
        !           583: It also allows input of a string not enclosed in quotes.
        !           584: The string must not start with a digit or quote,
        !           585: and can not contain any separators ( ``,'', ``/'', blank or tab ).
        !           586: A newline will terminate the string unless escaped with \\.
        !           587: Any string not meeting the above restrictions
        !           588: must be enclosed in quotes (`` " '' or `` \(fm '').
        !           589: .PP
        !           590: Internal list-directed I/O has been implemented. During internal list reads,
        !           591: bytes are consumed until the iolist is satisfied, or the ``end-of-file''
        !           592: is reached.
        !           593: During internal list writes, records are filled until the iolist is satisfied.
        !           594: The length of an internal array element should be at least 20 bytes to
        !           595: avoid logical record overflow when writing double precision values.
        !           596: Internal list read was implemented to make command line decoding easier.
        !           597: Internal list write should be avoided.
        !           598: .sp 1
        !           599: .Nh 1 "Running older programs"
        !           600: Traditional
        !           601: .Fo
        !           602: environments usually assume carriage control on all logical units,
        !           603: usually interpret blank spaces on input as ``0''s, and often provide
        !           604: attachment of global file names to logical units at run time.
        !           605: There are several routines in the I/O library to provide these functions.
        !           606: .Nh 2 "Traditional unit control parameters"
        !           607: If a program reads and writes only units 5 and 6, then including
        !           608: .B \-lI66
        !           609: in the f77 command will cause carriage control to be interpreted on
        !           610: output and cause blanks to be zeros on input without further
        !           611: modification of the program.
        !           612: If this is not adequate,
        !           613: the routine 'ioinit'(3f) can be called to specify control parameters
        !           614: separately, including whether files should be positioned at their
        !           615: beginning or end upon opening.
        !           616: .Nh 2 "Ioinit()"
        !           617: \&'Ioinit'(3f) can be used to attach logical units
        !           618: to specific files at run time, and to set global parameters for the
        !           619: .Sm I/O
        !           620: system.
        !           621: It will look for names of a user specified form in the environment
        !           622: and open the corresponding logical unit for
        !           623: .B "sequential formatted"
        !           624: I/O.
        !           625: Names must be of the form
        !           626: .B PREFIXnn
        !           627: where
        !           628: .B PREFIX
        !           629: is specified in the call to
        !           630: .I ioinit
        !           631: and
        !           632: .I nn
        !           633: is the logical unit to be opened. Unit numbers < 10 must include
        !           634: the leading ``0''.
        !           635: .PP
        !           636: .I Ioinit
        !           637: should prove adequate for most programs as written.
        !           638: However, it
        !           639: is written in
        !           640: .Fo \-77
        !           641: specifically so that it may serve as an example for similar
        !           642: user-supplied routines.
        !           643: A copy may be retrieved by ``ar x /usr/lib/libU77.a ioinit.f''.
        !           644: See section 2.4 for another way to override program file names
        !           645: through environment variables.
        !           646: .sp 1
        !           647: .Nh 1 "Magnetic tape I/O"
        !           648: Because the I/O library uses stdio buffering, reading or writing
        !           649: magnetic tapes should be done with great caution, or avoided if possible.
        !           650: A set of routines has been provided to read and write arbitrary sized buffers
        !           651: to or from tape directly. The buffer must be a
        !           652: .B character
        !           653: object.
        !           654: .B Internal
        !           655: I/O can be used to fill or interpret the buffer.
        !           656: These routines do not use normal
        !           657: .Fo
        !           658: I/O processing and do not obey
        !           659: .Fo
        !           660: I/O rules.
        !           661: See 'topen'(3f).
        !           662: .sp 1
        !           663: .Nh 1 "Caveat Programmer"
        !           664: The I/O library is extremely complex yet we believe there are few bugs left.
        !           665: We've tried to make the system as correct as possible according to
        !           666: the
        !           667: .Sm ANSI
        !           668: X3.9\-1978 document and keep it compatible with the
        !           669: .UX
        !           670: file system.
        !           671: .LP
        !           672: .ce 1
        !           673: Exceptions to the ANSI Standard
        !           674: .sp 1
        !           675: .PP
        !           676: A few exceptions to the
        !           677: .Sm ANSI
        !           678: standard remain.
        !           679: .LP
        !           680: 1) Vertical format control
        !           681: .PP
        !           682: The ``+'' carriage control specifier is not fully implemented
        !           683: (see section 2.3).
        !           684: It would be difficult to implement it correctly and still
        !           685: provide
        !           686: .UX -like
        !           687: file I/O.
        !           688: .PP
        !           689: Furthermore, the carriage control implementation is asymmetrical.
        !           690: A file written with carriage control interpretation can not be
        !           691: read again with the same characters in column 1.
        !           692: .PP
        !           693: An alternative to interpreting carriage control internally is to
        !           694: run the output file through a ``Fortran output filter''
        !           695: before printing. This filter could recognize a much broader range
        !           696: of carriage control and include terminal dependent processing.
        !           697: One such filter is 'fpr'(1).
        !           698: .sp 1
        !           699: .LP
        !           700: 2) Default files
        !           701: .PP
        !           702: Files created by default use of
        !           703: .B rewind
        !           704: or
        !           705: .B endfile
        !           706: statements are opened for
        !           707: .B "sequential formatted"
        !           708: access. There is no way to redefine such a file to allow
        !           709: .B direct
        !           710: or
        !           711: .B unformatted
        !           712: access.
        !           713: .sp 1
        !           714: .LP
        !           715: 3) Lower case strings
        !           716: .PP
        !           717: It is not clear if the
        !           718: .Sm ANSI
        !           719: standard requires internally generated strings to be upper case or not.
        !           720: As currently written, the
        !           721: .B inquire
        !           722: statement will return lower case strings for any alphanumeric data.
        !           723: .sp 1
        !           724: .LP
        !           725: 4) Exponent representation on Ew.dEe output
        !           726: .PP
        !           727: If the field width for the exponent is too small, the standard
        !           728: allows dropping the exponent character but only if the exponent
        !           729: is > 99. This system does not enforce that restriction.
        !           730: Further, the standard implies that the entire field, `w', should be
        !           731: filled with asterisks if the exponent can not be displayed.
        !           732: This system fills only the exponent field in the above case since
        !           733: that is more diagnostic.

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