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1.1 ! root 1: .ND ! 2: .TL ! 3: Update to the f77 I/O Library ! 4: January 1980 ! 5: .AU ! 6: David L. Wasley ! 7: .AI ! 8: University of California ! 9: Berkeley, Calif. 94720 ! 10: .PP ! 11: The fortran-77 I/O library, libI77.a, has been extensively updated. ! 12: All known bugs have been fixed, and ! 13: I/O error reporting has been improved. ! 14: Several non-standard extensions to FORTRAN I/O have been added. ! 15: .PP ! 16: Some general concepts regarding f77 I/O deserve clarification. There are three ! 17: forms of I/O: formatted, unformatted, and list-directed. The last is ! 18: related to formatted but does not obey all the rules for formatted I/O. ! 19: There are two modes of access to external and internal files: direct ! 20: and sequential. The definition of a logical record depends upon the ! 21: combination of I/O form and mode specified by the fortran I/O statement. ! 22: .PP ! 23: A logical record in direct access external files is a string of bytes ! 24: of a length specified when the file is opened. ! 25: Read and write statements must not specify logical records longer than ! 26: the original record size definition. Shorter logical records are allowed. ! 27: Unformatted direct writes leave the unfilled part of the record undefined. ! 28: Formatted direct writes cause the unfilled record to be padded with blanks. ! 29: .PP ! 30: Logical records in sequentially accessed external files may be of arbitrary ! 31: and variable length. ! 32: Logical record length for unformatted sequential files is determined by ! 33: the size of items in the iolist. ! 34: For formatted write statements, logical record length is determined by ! 35: the format statement interacting with the iolist at execution time. ! 36: Formatted sequential access causes one or more logical records ! 37: ending with 'newline' characters to be read or written. ! 38: .PP ! 39: Logical record length for list-directed I/O is relatively meaningless. ! 40: On output, the record length is dependent on the magnitude of the ! 41: data items. ! 42: On input, the record length is determined by the data types and the file ! 43: contents. ! 44: .PP ! 45: The logical record length for "internal" files is the length of the ! 46: character variable or array element. Thus a simple character variable ! 47: is a single logical record. A character variable array is similar to ! 48: a fixed length direct access file, and obeys the same rules. ! 49: Unformatted I/O is not allowed on "internal" files. ! 50: .PP ! 51: Note that each execution of a fortran unformatted I/O statement causes a single ! 52: logical record to be read or written. Each execution of a fortran formatted ! 53: I/O statement causes one or more logical records to be read or written. ! 54: .PP ! 55: Any error detected during I/O processing will cause the program to abort ! 56: unless alternate action has been provided for specifically in the program. ! 57: Any I/O statement may include an err= clause (and iostat= clause) ! 58: to specify an ! 59: alternate branch to be taken on errors (and return the specific error code). ! 60: Read or write statements may include end= to branch on end-of-file. ! 61: File position and the value of I/O list items is undefined following an error. ! 62: ! 63: I. Implementation details. ! 64: .PP ! 65: The maximum number of logical units that a program may have open at one ! 66: time has been set to correspond with the UNIX system limit, currently 20. ! 67: However, the I/O library uses UNIX file access for internal purposes. ! 68: Therefore fatal errors are possible if the maximum number of files are open. ! 69: Specifically, 'close' or 'endfile' on an old file, ! 70: and "'inquire' by file" may fail. ! 71: .PP ! 72: Vertical format control is implemented. The logical unit must be opened ! 73: for sequential access and "form = 'print'" (see below). ! 74: Control codes '0' and '1' are replaced in the output file ! 75: with '\\n' and '\\f' respectively. ! 76: The control character '+' isn't implemented and, like ! 77: any other character in the first position of a record ! 78: written to a "print" file, is dropped. ! 79: No vertical format control is recognized for direct formatted output ! 80: or list directed output. ! 81: .PP ! 82: Default logical units 0, 5, and 6 can be re-defined with an 'open' statement. ! 83: To preserve error reporting, it is an error to close logical unit 0. ! 84: If you want to open the default filename for any preconnected logical unit, ! 85: remember to 'close' the unit first. ! 86: Redefining the standard units may impair normal console I/O. ! 87: An alternative is to ! 88: use shell re-direction to externally re-define the above units. ! 89: To re-define default blank control or format of the standard input or output ! 90: files, use the 'open' statement specifying the unit number and no ! 91: filename (see below). ! 92: .PP ! 93: An 'open' statement need not specify a filename. If it refers to a logical ! 94: unit that is already open, the "blank= " and "form= " specifiers may be ! 95: redefined without affecting the current file position. ! 96: Otherwise, if "status='scratch'" is specified, a temporary file with a ! 97: name of the form 'tmp.FXXXXXX' will be opened, ! 98: and, by default, will be deleted when closed or during ! 99: termination of program execution. ! 100: Any other "status= " specifier without an associated filename results in ! 101: opening a file named 'fort.N' where N is the specified logical unit number. ! 102: It is an error to try to open an existing file with "status='new'". ! 103: It is an error to try to open a nonexistent file with "status='old'". ! 104: By default "status='unknown'" will be assumed, and a file will be created ! 105: if necessary. ! 106: Existing files are never truncated on opening but are positioned ! 107: at the end-of-file. ! 108: .PP ! 109: Sequentially accessed external files are truncated to the current file ! 110: position on 'close', 'backspace', or 'rewind' only if the last ! 111: access to the file was a write. ! 112: .PP ! 113: Upper as well as lower case characters are recognized in format statements ! 114: and all alphabetic arguments to the I/O library routines. ! 115: This has always been true for statements that are ! 116: part of the source code, but not for format statements ! 117: or character arguments from a file. ! 118: .PP ! 119: If the external representation of a datum ! 120: is too large for the field width specified, the specified ! 121: field is filled with asterisks (*). ! 122: On 'Ew.dEe' output, the e field will be filled with asterisks if the ! 123: exponent representation is too large. ! 124: (This will only happen if e==0) ! 125: .PP ! 126: List-directed output of complex values now includes an appropriate comma. ! 127: List-directed output now distinguishes between real*4 and real*8 values ! 128: and formats them differently. ! 129: Output of a character string that includes '\\n' now works correctly. ! 130: .PP ! 131: If I/O errors are not trapped by the user's program an appropriate ! 132: error message will be written to 'stderr' before aborting. ! 133: An error number will be printed in [ ] along with a brief error message ! 134: showing the logical unit and I/O state. ! 135: Error numbers < 100 refer to UNIX errors, and are described in the ! 136: introduction to chapter 2 of the UNIX Programmer's Manual. ! 137: Error numbers >= 100 come from the I/O library, and are described ! 138: further in the appendix to this writeup. ! 139: For internal I/O, part of the string will be printed with '|' at the ! 140: current position in the string. ! 141: For external I/O, part of the current record will be displayed if ! 142: the error was caused during reading from a file that can backspace. ! 143: .PP ! 144: Direct access list-directed I/O is not allowed. ! 145: Unformatted internal I/O is not allowed. ! 146: Both the above will be caught by the compiler. ! 147: All other flavors of I/O are allowed, although some are not part of the ANSI ! 148: standard. ! 149: .PP ! 150: The standard units, 0, 5, and 6, are now named internally 'stderr', 'stdin', ! 151: and 'stdout' respectively. ! 152: These are not actual filenames and can not be used for opening these units. ! 153: \'inquire' will not return these names and will indicate ! 154: that the above units are not named unless they have been opened to real files. ! 155: The names are meant to make error reporting more meaningful. ! 156: .PP ! 157: On output, a real value that is truly zero will display as '0.' to ! 158: distinguish it from a very small non-zero value. ! 159: This occurs in 'F', 'E', 'D', and 'G' format conversions. ! 160: .PP ! 161: Non-destructive tabbing is implemented for both internal and external ! 162: formatted I/O. ! 163: Tabbing left or right on output ! 164: does not affect previously written portions of a record. ! 165: Tabbing right on output ! 166: causes unwritten portions of a record to be filled with blanks. ! 167: Tabbing left or right off the end of a logical record is an error. ! 168: The format specifier 'T' must be followed by a positive non-zero number. ! 169: If it is not, it will have a different meaning (See below). ! 170: Note that spacing with 'X' always writes blanks in the output record. ! 171: ! 172: II. Non-"ANSI Standard" Extensions ! 173: .PP ! 174: B is an acceptable edit control specifier. It causes return to the ! 175: default mode of blank interpretation (NULL) and is identical to BN. ! 176: This is consistent with S which returns to default sign control. ! 177: .PP ! 178: P by itself is equivalent to 0P. It resets the scale factor to the ! 179: default value, 0. ! 180: .PP ! 181: The form of the 'Ew.dEe' format specifier has been extended to 'D' also. ! 182: The form 'Ew.d.e' is allowed but is not standard. ! 183: The 'e' field specifies the minimum number of digits or spaces in the ! 184: exponent field on output. ! 185: If the value of the exponent is too large, the exponent notation 'e' ! 186: or 'd' will be dropped from the output to allow one ! 187: more character position. ! 188: If this is still not adequate, the 'e' field will be filled with ! 189: asterisks (*). The default value for 'e' is 2. ! 190: .PP ! 191: An additional form of tab control specification has been added. ! 192: The ANSI standard forms 'TRn', 'TLn', and 'Tn' are supported where n is ! 193: a positive non-zero number. If 'T' or 'nT' is specified, tabbing will ! 194: be to the next (or n-th) 8-column tab stop. ! 195: Thus columns of alphanumerics can be lined up without counting. ! 196: (See above for a description of the tabbing implementation.) ! 197: .PP ! 198: A format control specifier has been added to suppress the newline ! 199: at the end of the last record of a formatted sequential write. The ! 200: specifier is a dollar sign ($). It is constrained by the same rules ! 201: as the colon (:). It is used typically for console prompts. ! 202: For example: ! 203: ! 204: .DS ! 205: write (*, "('enter value for x: ',$)") ! 206: read (*,*) x ! 207: .DE ! 208: .PP ! 209: Radices other than 10 can be specified for formatted integer I/O ! 210: conversion. The specifier is patterned after P, the pre-scale factor for ! 211: floating point conversion. It remains in effect until another radix is ! 212: specified or format interpretation is complete. The specifier is defined ! 213: as [n]R where 2 <= n <= 36. If n is omitted, ! 214: the default decimal radix is restored. ! 215: .PP ! 216: In conjunction with the above, a sign control specifier has been added ! 217: to cause integer values to be interpreted as unsigned during output ! 218: conversion. The specifier is SU and remains in effect until another ! 219: sign control specifier is encountered, or format interpretation is ! 220: complete. Radix and 'unsigned' specifiers could be used to format ! 221: a hexadecimal dump, as follows: ! 222: ! 223: .DS ! 224: 2000 format( SU, 16R, 8I10.8) ! 225: .DE ! 226: ! 227: Note: Unsigned integer values greater than (2**30 - 1), ! 228: i.e. any signed negative value, can not be read by FORTRAN input routines. ! 229: All internal values will be output correctly. ! 230: .PP ! 231: The ANSI standard is ambiguous regarding the definition of a "print" file. ! 232: Since UNIX has no default "print" file, an additional 'form' specifier ! 233: is now recognized in the 'open' statement. ! 234: Specifying "form='print'" implies 'formatted' and enables vertical format ! 235: control for that logical unit (see above). ! 236: Vertical format control is interpreted only on sequential formatted writes ! 237: to a "print" file. ! 238: .PP ! 239: The 'inquire' statement will return 'print' in the 'FORM=' string variable ! 240: for logical units opened as "print" files. ! 241: It will return -1 for the unit number of an unconnected file. ! 242: .PP ! 243: If a logical unit is already open, an 'open' statement including the ! 244: 'form=' option or the 'blank=' option will do nothing but ! 245: re-define those options. ! 246: This instance of the 'open' statement need not include the filename, and ! 247: must not include a filename if 'unit=' refers to the standard input or outputs. ! 248: Therefore, to re-define the standard output as a "print" file, use: ! 249: ! 250: .DS ! 251: open (unit=6, form='print') ! 252: .DE ! 253: .PP ! 254: In a 'close' statement, "status='keep'" may be specified for temporary files. ! 255: This is the default for all other files. ! 256: Remember to get the file's real name, ! 257: using 'inquire', if you want to re-open it later. ! 258: .PP ! 259: List directed read has been modified to allow input of a string not enclosed ! 260: in quotes. The string must not start with a digit, and can not contain a ! 261: separator (, or /) or blank (space or tab). A newline will terminate the ! 262: string unless escaped with \\. Any string not meeting the above restrictions ! 263: must be enclosed in quotes (" or '). ! 264: .PP ! 265: Internal list-directed I/O has been implemented. During internal list reads, ! 266: bytes are consummed until the iolist is satisfied, or the 'end-of-file' ! 267: is reached. ! 268: During internal list writes, records are filled until the iolist is satisfied. ! 269: The length of an internal array element should be at least 20 bytes to ! 270: avoid logical record overflow when writing double precision values. ! 271: Internal list read was implemented to make command line decoding easier. ! 272: Internal list write should be avoided. ! 273: .bp ! 274: .ce 2 ! 275: Appendix A ! 276: I/O Library Error Messages ! 277: .PP ! 278: The following error messages are generated by the I/O library. ! 279: The error numbers are returned in the "iostat=" variable if the "err=" ! 280: return is taken. Error numbers < 100 are generated by UNIX. See the ! 281: UNIX Programmers Manual, introduction to chapter 2. ! 282: .DS ! 283: /* 100 */ "error in format" ! 284: See error message output for the location ! 285: of the error in the format. Can be caused ! 286: by more than 10 levels of nested (), or ! 287: an extremely long format statement. ! 288: ! 289: /* 101 */ "illegal unit number" ! 290: It is illegal to close logical unit 0. ! 291: Negative unit numbers are not allowed. ! 292: The upper limit is system dependent. ! 293: ! 294: /* 102 */ "formatted io not allowed" ! 295: The logical unit was opened for ! 296: unformatted I/O. ! 297: ! 298: /* 103 */ "unformatted io not allowed" ! 299: The logical unit was opened for ! 300: formatted I/O. ! 301: ! 302: /* 104 */ "direct io not allowed" ! 303: The logical unit was opened for sequential ! 304: access, or the logical record length was ! 305: specified as 0. ! 306: ! 307: /* 105 */ "sequential io not allowed" ! 308: The logical unit was opened for direct ! 309: access I/O. ! 310: ! 311: /* 106 */ "can't backspace file" ! 312: The file associated with the logical unit ! 313: can't seek. May be a device or a pipe. ! 314: ! 315: /* 107 */ "off beginning of record" ! 316: The format specified a left tab off the ! 317: beginning of the record. ! 318: ! 319: /* 108 */ "can't stat file" ! 320: The system can't return status information ! 321: about the file. Perhaps the directory is ! 322: unreadable. ! 323: ! 324: /* 109 */ "no * after repeat count" ! 325: Repeat counts in list-directed I/O must be ! 326: followed by an * with no blank spaces. ! 327: ! 328: .DE ! 329: .DS ! 330: /* 110 */ "off end of record" ! 331: A formatted write tried to go beyond the ! 332: logical end-of-record. An unformatted read ! 333: or write will also cause this. ! 334: ! 335: /* 111 */ "truncation failed" ! 336: The truncation of external sequential files ! 337: on 'close', 'backspace', or 'rewind' tries ! 338: to do a copy. It failed. Perhaps the temp ! 339: file couldn't be created. ! 340: ! 341: /* 112 */ "incomprehensible list input" ! 342: List input has to be just right. ! 343: ! 344: /* 113 */ "out of free space" ! 345: The library dynamically creates buffers for ! 346: internal use. You ran out of memory for this. ! 347: Your program is too big! ! 348: ! 349: /* 114 */ "unit not connected" ! 350: The logical unit was not open. ! 351: ! 352: /* 115 */ "read unexpected character" ! 353: Certain format conversions can't tolerate ! 354: non-numeric data. Logical data must be ! 355: T or F. ! 356: ! 357: /* 116 */ "blank logical input field" ! 358: ! 359: /* 117 */ "'new' file exists" ! 360: You tried to open an existing file with ! 361: "status='new'". ! 362: ! 363: /* 118 */ "can't find 'old' file" ! 364: You tried to open a non-existent file ! 365: with "status='old'". ! 366: ! 367: /* 119 */ "unknown system error" ! 368: Shouldn't happen, but ..... ! 369: (Send me a documented example.) ! 370: ! 371: /* 120 */ "requires seek ability" ! 372: Direct access requires seek ability. ! 373: Sequential unformatted I/O requires seek ! 374: ability on the file due to the special ! 375: data structure required. Tabbing left ! 376: also requires seek ability. ! 377: ! 378: /* 121 */ "illegal argument" ! 379: Certain arguments to 'open', etc. will be ! 380: checked for legitimacy. Often only non- ! 381: default forms are looked for. ! 382: .DE
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