Copyright (c) 1985, 1993
The Regents of the University of California. All rights reserved.

%sccs.include.proprietary.man%

@(#)f77IO.ms 8.3 (Berkeley) 06/01/94

.EH 'PSD:9-%''Introduction to the f77 I/O Library' .OH 'Introduction to the f77 I/O Library''PSD:9-%' Fortran\\$1 .. \s-1\\$1\s0 ..
Nh macro - same as NH but also saves heading for table of contents
Nh usage: Nh level string, e.g.: .Nh 2 "Calculator Sample"
\\$2 .XS \\*(SN \\$2 .XE

.. .ND "" .nr ll 7.0i
.nr LL 7.0i
.po 0.0i
.rm PT
.rm BT
.RP

Introduction to the f77 I/O Library .AU David L. Wasley .AU J. Berkman .AI University of California, Berkeley Berkeley, California 94720 .AB The f77 I/O library, libI77.a, includes routines to perform all of the standard types of .Fo input and output specified in the .Sm ANSI 1978 .Fo standard. The I/O Library was written originally by Peter J. Weinberger at Bell Labs. Where the original implementation was incomplete, it has been rewritten to more closely implement the standard. Where the standard is vague, we have tried to provide flexibility within the constraints of the X operating system. A number of logical extensions and enhancements have been provided such as the use of the C stdio library routines to provide efficient buffering for file I/O.

Revised September, 1985 .AE

page 2 is allocated to the table of contents
.bp .Nh 1 "Fortran I/O" The requirements of the .Sm ANSI standard impose significant overhead on programs that do large amounts of I/O. Formatted I/O can be very ``expensive'' while direct access binary I/O is usually very efficient. Because of the complexity of .Fo I/O, some general concepts deserve clarification. .Nh 2 "Types of I/O and logical records" There are four forms of I/O: formatted, unformatted, list directed, and namelist. The last two are related to formatted but do not obey all the rules for formatted I/O. There are two types of ``files'': external and internal and two modes of access to files: direct and sequential. The definition of a logical record depends upon the combination of I/O form, file type, and access mode specified by the .Fo I/O statement. .Nh 3 "Direct access external I/O" A logical record in a direct access external file is a string of bytes of a length specified when the file is opened. Read and write statements must not specify logical records longer than the original record size definition. Shorter logical records are allowed. Unformatted direct writes leave the unfilled part of the record undefined. Formatted direct writes cause the unfilled record to be padded with blanks. .Nh 3 "Sequential access external I/O" Logical records in sequentially accessed external files may be of arbitrary and variable length. Logical record length for unformatted sequential files is determined by the size of items in the iolist. The requirements of this form of I/O cause the external physical record size to be somewhat larger than the logical record size. For formatted write statements, logical record length is determined by the format statement interacting with the iolist at execution time. The ``newline'' character is the logical record delimiter. Formatted sequential access causes one or more logical records ending with ``newline'' characters to be read or written. .Nh 3 "List directed and namelist sequential external I/O" Logical record length for list directed and namelist I/O is relatively meaningless. On output, the record length is dependent on the magnitude of the data items. On input, the record length is determined by the data types and the file contents. By ANSI definition, a slash, ``/'', terminates execution of a list directed input operation. Namelist input is terminated by ``&end'' or ``$end'' (depending on whether the character before the namelist name was ``&'' or ``$''). .Nh 3 "Internal I/O" The logical record length for an internal read or write is the length of the character variable or array element. Thus a simple character variable is a single logical record. A character variable array is similar to a fixed length direct access file, and obeys the same rules. Unformatted and namelist I/O are not allowed on ``internal'' files. .Nh 2 "I/O execution" Note that each execution of a .Fo unformatted I/O statement causes a single logical record to be read or written. Each execution of a .Fo formatted I/O statement causes one or more logical records to be read or written.

A slash, ``/'', will terminate assignment of values to the input list during list directed input and the remainder of the current input line is skipped. The standard is rather vague on this point but seems to require that a new external logical record be found at the start of any formatted input. Therefore data following the slash is ignored and may be used to comment the data file.

"Direct access list directed" I/O is not allowed. "Unformatted internal" I/O is not allowed. Namelist I/O is allowed only with "external sequential" files. All other flavors of I/O are allowed, although some are not part of the .Sm ANSI standard.

Any I/O statement may include an err= clause to specify an alternative branch to be taken on errors and/or an iostat= clause to return the specific error code. Any error detected during I/O processing will cause the program to abort unless either err= or iostat= has been specificed in the program. Read statements may include end= to branch on end-of-file. The end-of-file indication for that logical unit may be reset with a backspace statement. File position and the value of I/O list items is undefined following an error. .Nh 1 "Implementation details" Some details of the current implementation may be useful in understanding constraints on .Fo I/O. .Nh 2 "Number of logical units" Unit numbers must be in the range 0 - 99. The maximum number of logical units that a program may have open at one time is the same as the X system limit, currently 48. .Nh 2 "Standard logical units" By default, logical units 0, 5, and 6 are opened to ``stderr'', ``stdin'', and ``stdout'' respectively. However they can be re-defined with an open statement. To preserve error reporting, it is an error to close logical unit 0 although it may be reopened to another file.

If you want to open the default file name for any preconnected logical unit, remember to close the unit first. Redefining the standard units may impair normal console I/O. An alternative is to use shell re-direction to externally re-define the above units. To re-define default blank control or format of the standard input or output files, use the open statement specifying the unit number and no file name (see \(sc\|2.4).

The standard units, 0, 5, and 6, are named internally ``stderr'', ``stdin'', and ``stdout'' respectively. These are not actual file names and can not be used for opening these units. Inquire will not return these names and will indicate that the above units are not named unless they have been opened to real files. The names are meant to make error reporting more meaningful. .Nh 2 "Vertical format control" Simple vertical format control is implemented. The logical unit must be opened for sequential access with "form = \(fmprint\(fm" (see \(sc\|3.2). Control codes ``0'' and ``1'' are replaced in the output file with ``\\n'' and ``\\f'' respectively. The control character ``+'' is not implemented and, like any other character in the first position of a record written to a ``print'' file, is dropped. The "form = \(fmprint\(fm" mode does not recognize vertical format control for "direct formatted, list directed," or "namelist" output.

An alternative is to use the filter fpr(1) for vertical format control. It replaces ``0'' and ``1'' by ``\\n'' and ``\\f'' respectively, and implements the ``+'' control code. Unlike "form = \(fmprint\(fm" which drops unrecognized form control characters, fpr copies those characters to the output file. .Nh 2 "File names and the open statement" A file name may be specified in an open statement for the logical unit. If a logical unit is opened by an open statement which does not specify a file name, or it is opened implicitly by the execution of a read, write, or endfile statement, then the default file name is fort.N where N is the logical unit number. Before opening the file, the library checks for an environment variable with a name identical to the tail of the file name with periods removed.\(dg .FS \(dgPeriods are deleted because they can not be part of environment variable names in the Bourne shell. .FE If it finds such an environment variable, it uses its value as the actual name of the file. For example, a program containing: open(32,file=\(fm/usr/guest/census/data.d\(fm) read(32,100) vec write(44) vec normally will read from /usr/guest/census/data.d and write to fort.44 in the current directory. If the environment variables datad and fort44 are set, e.g.: % setenv datad mydata % setenv fort44 myout in the C shell or: $ datad=mydata $ fort44=myout $ export datad fort44 in the Bourne shell, then the program will read from mydata and write to myout.

An open statement need not specify a file name. If it refers to a logical unit that is already open, the blank= and form= specifiers may be redefined without affecting the current file position. Otherwise, if "status = \(fmscratch\(fm" is specified, a temporary file with a name of the form tmp.FXXXXXX will be opened, and, by default, will be deleted when closed or during termination of program execution.

It is an error to try to open an existing file with "status = \(fmnew\(fm" . It is an error to try to open a nonexistent file with "status = \(fmold\(fm" . By default, "status = \(fmunknown\(fm" will be assumed, and a file will be created if necessary.

By default, files are positioned at their beginning upon opening, but see fseek(3f) and ioinit(3f) for alternatives. Existing files are never truncated on opening. Sequentially accessed external files are truncated to the current file position on close, backspace, or rewind only if the last access to the file was a write. An endfile always causes such files to be truncated to the current file position. .Nh 2 "Format interpretation" Formats which are in format statements are parsed by the compiler; formats in read, write, and print statements are parsed during execution by the .Sm I/O library. Upper as well as lower case characters are recognized in format statements and all the alphabetic arguments to the I/O library routines.

If the external representation of a datum is too large for the field width specified, the specified field is filled with asterisks (\(**). On Ew.dEe output, the exponent field will be filled with asterisks if the exponent representation is too large. This will only happen if ``e'' is zero (see appendix B).

On output, a real value that is truly zero will display as ``0.'' to distinguish it from a very small non-zero value. If this causes problems for other input systems, the BZ edit descriptor may be used to cause the field following the decimal point to be filled with zero's.

Non-destructive tabbing is implemented for both internal and external formatted I/O. Tabbing left or right on output does not affect previously written portions of a record. Tabbing right on output causes unwritten portions of a record to be filled with blanks. Tabbing right off the end of an input logical record is an error. Tabbing left beyond the beginning of an input logical record leaves the input pointer at the beginning of the record. The format specifier T must be followed by a positive non-zero number. If it is not, it will have a different meaning (see \(sc\|3.1).

Tabbing left requires seek ability on the logical unit. Therefore it is not allowed in I/O to a terminal or pipe. Likewise, nondestructive tabbing in either direction is possible only on a unit that can seek. Otherwise tabbing right or spacing with X will write blanks on the output. .Nh 2 "List directed output" In formatting list directed output, the I/O system tries to prevent output lines longer than 80 characters. Each external datum will be separated by two spaces. List directed output of complex values includes an appropriate comma. List directed output distinguishes between real and "double precision" values and formats them differently. Output of a character string that includes ``\\n'' is interpreted reasonably by the output system. .Nh 2 "I/O errors" If I/O errors are not trapped by the user's program an appropriate error message will be written to ``stderr'' before aborting. An error number will be printed in ``[ ]'' along with a brief error message showing the logical unit and I/O state. Error numbers < 100 refer to X errors, and are described in the introduction to chapter 2 of the X Programmer's Manual. Error numbers \(>= 100 come from the I/O library, and are described further in the appendix to this writeup\(dd. .FS \(dd On many systems, these are also available in help f77 io_err_msgs. .FE For internal I/O, part of the string will be printed with ``|'' at the current position in the string. For external I/O, part of the current record will be displayed if the error was caused during reading from a file that can backspace. .Nh 1 "Non-``ANSI Standard'' extensions" Several extensions have been added to the I/O system to provide for functions omitted or poorly defined in the standard. Programmers should be aware that these are non-portable. .Nh 2 "Format specifiers" B is an acceptable edit control specifier. It causes return to the logical unit's default mode of blank interpretation. This is consistent with S which returns to default sign control.

P by itself is equivalent to 0P . It resets the scale factor to the default value, 0.

The form of the Ew.dEe format specifier has been extended to D also. The form Ew.d.e is allowed but is not standard. The ``e'' field specifies the minimum number of digits or spaces in the exponent field on output. If the value of the exponent is too large, the exponent notation e or d will be dropped from the output to allow one more character position. If this is still not adequate, the ``e'' field will be filled with asterisks (\(**). The default value for ``e'' is 2.

An additional form of tab control specification has been added. The .Sm ANSI standard forms TRn, TLn, and Tn are supported where n is a positive non-zero number. If T or nT is specified, tabbing will be to the next (or n-th) 8-column tab stop. Thus columns of alphanumerics can be lined up without counting.

A format control specifier has been added to suppress the newline at the end of the last record of a formatted sequential write. The specifier is a dollar sign ($). It is constrained by the same rules as the colon (:). It is used typically for console prompts. For example: write (\(**, "(\(fmenter value for x: \(fm,$)") read (\(**,\(**) x

Radices other than 10 can be specified for formatted integer I/O conversion. The specifier is patterned after P, the scale factor for floating point conversion. It remains in effect until another radix is specified or format interpretation is complete. The specifier is defined as [n]R where 2 \(<= n \(<= 36. If n is omitted, the default decimal radix is restored.

The format specifier Om.n may be used for an octal conversion; it is equivalent to 8R,Im.n,10R. Similarly, Zm.n is equivalent to 16R,Im.n,10R and may be used for an hexadecimal conversion;

In conjunction with the above, a sign control specifier has been added to cause integer values to be interpreted as unsigned during output conversion. The specifier is SU and remains in effect until another sign control specifier is encountered, or format interpretation is complete.\(dg .FS \(dgNote: Unsigned integer values greater than (2\(**\(**31 - 1), can be read and written using SU. However they can not be used in computations because .Fo uses signed arithmetic and such values appear to the arithmetic unit as negative numbers. .FE Radix and ``unsigned'' specifiers could be used to format a hexadecimal dump, as follows: 2000 format ( SU, 8Z10.8 ) .Nh 2 "Print files" The .Sm ANSI standard is ambiguous regarding the definition of a ``print'' file. Since X has no default ``print'' file, an additional form= specifier is now recognized in the open statement. Specifying "form = \(fmprint\(fm" implies formatted and enables vertical format control for that logical unit (see \(sc\|2.3). Vertical format control is interpreted only on sequential formatted writes to a ``print'' file.

The inquire statement will return print in the form= string variable for logical units opened as ``print'' files. It will return -1 for the unit number of an unconnected file.

If a logical unit is already open, an open statement including the form= option or the blank= option will do nothing but re-define those options. This instance of the open statement need not include the file name, and must not include a file name if unit= refers to a standard input or output. Therefore, to re-define the standard output as a ``print'' file, use: open (unit=6, form=\(fmprint\(fm) .Nh 2 "Scratch files" A close statement with "status = \(fmkeep\(fm" may be specified for temporary files. This is the default for all other files. Remember to get the scratch file's real name, using inquire , if you want to re-open it later. .Nh 2 "List directed I/O" List directed read has been modified to allow tab characters wherever blanks are allowed. It also allows input of a string not enclosed in quotes. The string must not start with a digit or quote, and can not contain any separators ( ``,'', ``/'', blank or tab ). A newline will terminate the string unless escaped with \\. Any string not meeting the above restrictions must be enclosed in quotes (`` " '' or `` \(fm '').

Internal list directed I/O has been implemented. During internal list reads, bytes are consumed until the iolist is satisfied, or the ``end-of-file'' is reached. During internal list writes, records are filled until the iolist is satisfied. The length of an internal array element should be at least 20 bytes to avoid logical record overflow when writing double precision values. Internal list read was implemented to make command line decoding easier. Internal list write should be avoided. .Nh 2 "Namelist I/O" Namelist I/O is a common extension in Fortran systems. The f77 version was designed to be compatible with other vendors versions; it is described in ``A Portable Fortran 77 Compiler'', by Feldman and Weinberger, August, 1985. .Nh 1 "Running older programs" Traditional .Fo environments usually assume carriage control on all logical units, usually interpret blank spaces on input as ``0''s, and often provide attachment of global file names to logical units at run time. There are several routines in the I/O library to provide these functions. .Nh 2 "Traditional unit control parameters" If a program reads and writes only units 5 and 6, then including -lI66 in the f77 command will cause carriage control to be interpreted on output and cause blanks to be zeros on input without further modification of the program. If this is not adequate, the routine ioinit(3f) can be called to specify control parameters separately, including whether files should be positioned at their beginning or end upon opening. .Nh 2 "Ioinit()" Ioinit(3f) can be used to attach logical units to specific files at run time, and to set global parameters for the .Sm I/O system. It will look for names of a user specified form in the environment and open the corresponding logical unit for "sequential formatted" I/O. Names must be of the form \s-1PREFIX\s0nn where \\s-1PREFIX\\s0 is specified in the call to ioinit and nn is the logical unit to be opened. Unit numbers < 10 must include the leading ``0''.

Ioinit should prove adequate for most programs as written. However, it is written in .Fo -77 specifically so that it may serve as an example for similar user-supplied routines. A copy may be retrieved by ``ar x /usr/lib/libU77.a ioinit.f''. See \(sc\|2.4 for another way to override program file names through environment variables. .Nh 1 "Magnetic tape I/O" Because the I/O library uses stdio buffering, reading or writing magnetic tapes should be done with great caution, or avoided if possible. A set of routines has been provided to read and write arbitrary sized buffers to or from tape directly. The buffer must be a character object. Internal I/O can be used to fill or interpret the buffer. These routines do not use normal .Fo I/O processing and do not obey .Fo I/O rules. See topen(3f). .Nh 1 "Caveat Programmer" The I/O library is extremely complex yet we believe there are few bugs left. We've tried to make the system as correct as possible according to the .Sm ANSI X3.9-1978 document and keep it compatible with the X file system. Exceptions to the standard are noted in appendix B. .bp C "Appendix A" "I/O Library Error Messages" .XS Appendix A: I/O Library Error Messages .XE

The following error messages are generated by the I/O library. The error numbers are returned in the iostat= variable. Error numbers < 100 are generated by the X kernel. See the introduction to chapter 2 of the X Programmers Manual for their description. .nr PD 0

\\$2

..

.bp

C "Appendix B" "Exceptions to the ANSI Standard" .XS Appendix B: Exceptions to the ANSI Standard .XE

A few exceptions to the .Sm ANSI standard remain.

"Vertical format control"

The ``+'' carriage control specifier is not fully implemented (see \(sc\|2.3). It would be difficult to implement it correctly and still provide X -like file I/O.

Furthermore, the carriage control implementation is asymmetrical. A file written with carriage control interpretation can not be read again with the same characters in column 1.

An alternative to interpreting carriage control internally is to run the output file through a ``Fortran output filter'' before printing. This filter could recognize a much broader range of carriage control and include terminal dependent processing. One such filter is fpr(1).

"Default files"

Files created by default use of endfile statements are opened for "sequential formatted" access. There is no way to redefine such a file to allow direct or unformatted access.

"Lower case strings"

It is not clear if the .Sm ANSI standard requires internally generated strings to be upper case or not. As currently written, the inquire statement will return lower case strings for any alphanumeric data.

"Exponent representation on Ew.dEe output"

If the field width for the exponent is too small, the standard allows dropping the exponent character but only if the exponent is > 99. This system does not enforce that restriction. Further, the standard implies that the entire field, ``w'', should be filled with asterisks if the exponent can not be displayed. This system fills only the exponent field in the above case since that is more diagnostic.

"Pre-connection of files"

The standard says units must be pre-connected to files before the program starts or must be explicitly opened. Instead, the I/O library connects the unit to a file on its first use in a read, write, print, or endfile statement. Thus inquire by unit can not tell prior to a unit number use the characteristics or name of the file corresponding to a unit. want Table of Contents to begin on page 2 hence must expand body
of .TC macro to enable us to get handle on page number.
.bp

X