# I/O Options and Subcase Information Entries Guidelines

The following guidelines apply to all entries in the I/O Options and Subcase Information sections.

• All input cards are limited to 80 characters per line; all characters after the 80th are skipped. SYSSETTING,CARDLENGTH, may be used to change the number of characters allowed in each line.
• "Tab" spaces are not allowed and may lead OptiStruct to error out, if present.
• Cards which require a file name (OUTFILE, RESTART, INCLUDE, LOADLIB, TMPDIR, EIGVNAME, ASSIGN) can contain up to 200 characters in a single line. Alternatively, the file name may be continued in several lines if it is enclosed in quotes (" or '). When combining continuation lines, all trailing and leading blanks in each line are omitted. File names with blanks at the start or end are not allowed, even if enclosed in quotes.
• File names can contain an absolute or relative path. Forward slash (/) or back slash (\) characters can be used to separate parts of a path name. Absolute paths are discouraged since they prevent moving files from one location to another, and may cause unexpected failures, as in PBS or a similar batch environment.
• Windows style file names, starting with the drive letter (for example: D:/users/mbg/workarea), can be used on Unix/ Linux only when environment variable(s) DOS_DRIVE_# are defined. Content of the respective environment variable replaces the first two letters ('D:') in the file name, and the expanded file name must fit within 600 characters. Alternatively, the DOS_DRIVE_# option can be specified in the config file. UNC format (//server/path/filename) is not accepted.
• Each line of data contains up to ten fields in free format. Entries in the free format are separated by any number of characters from the following set:
• (blank)
• , (comma)
• (
• )
• =

File names and titles (TITLE, SUBTITLE, and LABEL) are exceptions to this rule.

• P2G, K2GG, M2GG, and B2GG entries allow more than ten fields per line (up to CARDLENGTH limit).
• GROUNDCHECK, WEIGHTCHECK, EIGVRETRIEVE, and XYPLOT allow more than ten fields per line and are the only entries which allow continuation.
• Dollar signs, \$, in any column denote comments. All characters after the dollar sign until the end of the line are ignored. A dollar sign can be a part of a file name or title, but the full title or file name must be enclosed in quotes (" or ') in such cases.
• Lines which begin with two slashes, //, or a pound symbol, #, are read as comment lines. Blank lines are also assumed to be comment lines.
• Continuation lines are marked with a trailing comma character in the preceding line.
• Integer entries may not contain decimal points or exponent parts, and must fit in the range of values allowed for INTEGER*4 (usually -2**31<x<2**31).
• Integer data placed in the field reserved for real valued data is accepted and converted to a double precision.
• Character entries longer than eight characters are silently truncated, except for the title strings and file names. All character strings, except user-provided labels, titles, and file names, are case insensitive (can be typed in lower or upper case). File names are always case sensitive, except with Windows, where the operating system does not care for case.
• Abbreviated keyword entries are accepted and recognized properly using the first four characters. When a four character abbreviation is not unique, the full length keyword has to appear on the data line (but only the first eight characters are used if the keyword is longer).

## Examples

The following three lines are equivalent:
DISPLACEMENT (form) = option
disp FORM option
displa ,, form , oPTIOn
The following is a card with multiple continuation lines:
XYPLOT, XYPEAK, VELO, PSDF / 3(T2),
6(T2), 8(T2), 10(T2),
20(T2)
The following is a path split across several lines:
INCLUDE "path/
/split into multiple / lines
/filename.txt "
is equivalent to:
INCLUDE "path//split into multiple / lines/filename.txt "
Note: Several spaces, the space at the end in particular, which are valid parts of this name, may cause unexpected results.