Language Reference

Interaction between Input/Output Lists and Format Specifications

The beginning of format-directed formatting initiates format control. Each action of format control depends on the next edit descriptor contained in the format specification and on the next item in the input/output list, if one exists.

If an input/output list specifies at least one item, at least one data edit descriptor must exist in the format specification. Note that an empty format specification (parentheses only) can be used only if there are no items in the input/output list or if each item is a zero-sized array. If this is the case and advancing input/output is in effect, one input record is skipped, or one output record containing no characters is written. For nonadvancing input/output, the file position is left unchanged.

A format specification is interpreted from left to right, except when a repeat specification (r) is present. A format item that is preceded by a repeat specification is processed as a list of r format specifications or edit descriptors identical to the format specification or edit descriptor without the repeat specification.

One item specified by the input/output list corresponds to each data edit descriptor. A list item of type complex requires the interpretation of two F, E, EN, ES, D, G, or extended precision Q edit descriptors. No item specified by the input/output list corresponds to a control edit descriptor or character string edit descriptor. Format control communicates information directly with the record.

Format control operates as follows:

1. If a data edit descriptor is encountered, format control processes an input/output list item, if there is one, or terminates the input/output command if the list is empty. If the list item processed is of type complex, any two edit descriptors are processed.
2. The colon edit descriptor terminates format control if no more items are in the input/output list. If more items are in the input/output list when the colon is encountered, it is ignored.
3. If the end of the format specification is reached, format control terminates if the entire input/output list has been processed, or control reverts to the beginning of the format item terminated by the last preceding right parenthesis. The following items apply when the latter occurs:
   • The reused portion of the format specification must contain at least one data edit descriptor.
   • If reversion is to a parenthesis that is preceded by a repeat specification, the repeat specification is reused.
   • Reversion, of itself, has no effect on the scale factor, on the S, SP, or SS edit descriptors, or on the BN or BZ edit descriptors.
   • If format control reverts, the file is positioned in a manner identical to the way it is positioned when a slash edit descriptor is processed.

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During a read operation, any unprocessed characters of the record are skipped whenever the next record is read. A comma can be used as a value separator for noncharacter data in an input record processed under format-directed formatting. The comma will override the format width specifications when the comma appears before the end of the field width. For example, the format (I10,F20.10,I4) will read the following record correctly:

-345, .05E-3, 12

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It is important to consider the maximum size record allowed on the input/output medium when defining a Fortran record by a FORMAT statement. For example, if a Fortran record is to be printed, the record should not be longer than the printer's line length.