Combinations of I/O (FORTRAN 77 Language Reference)

FORTRAN 77 Language Reference

Combinations of I/O

I/O combinations on external files are:

Allowed	Not Allowed
Sequential unformatted Sequential formatted Sequential list-directed Sequential `NAMELIST` Direct unformatted Direct formatted	Direct-access, list-directed I/O Direct-access, `NAMELIST` I/O `NAMELIST` I/O on internal files Unformatted, internal I/O

The following table shows combinations of I/O form, access mode, and physical file types.

Table 5-1 Summary of f77 Input and Output


Kind of I/O		Access Mode:
Form	File Type	Sequential	Direct
Formatted	Internal	The file is a character variable, substring, array, or array element. `@`	The file is a character array; each record is one array element.
Formatted	External	Only formatted records of same or variable length.	Only formatted records, all the same length.
Unformatted	Internal	Not allowed.	Not allowed.
Unformatted	External	Contains only unformatted records.	`READ`: Gets one logical record at a time. `WRITE`: Unfilled part of record is undefined.
List-directed	Internal	`READ`: Reads characters until EOF or I/O list is satisfied. `WRITE`: Writes records until list is satisfied. `@`	Not allowed.
List-directed	External	Uses standard formats based on type of variable and size of element. Blanks or commas are separators. Any columns.	Not allowed.
`NAMELIST`	Internal	Not allowed.	Not allowed.
`NAMELIST`	External	`READ`: Reads records until it finds `$`groupname in columns 2-80. Then reads records searching for names in that group, and stores data in those variables. Stops reading on `$` or `eof`. `WRITE`: Writes records showing the group name and each variable name with value.	Not allowed.

Avoid list-directed internal writes. The number of lines and items per line varies with the values of items.