2.1.2 Opening Files Without a Name

The OPEN statement need not specify a name; the runtime system supplies a file name according to several conventions.

2.1.2.1 Opened as Scratch

Specifying STATUS=’SCRATCH’ in the OPEN statement opens a file with a name of the form tmp.FAAAxnnnnn, where nnnnn is replaced by the current process ID, AAA is a string of three characters, and x is a letter; the AAA and x make the file name unique. This file is deleted upon termination of the program or execution of a CLOSE statement. When compiling in FORTRAN 77 compatibility mode (-f77), you can specify STATUS=’KEEP’ in the CLOSE statement to preserve the scratch file. (This is a non-standard extension.)

2.1.2.2 Already Open

If the file has already been opened by the program, you can use a subsequent OPEN statement to change some of the file’s characteristics; for example, BLANK and FORM. In this case, you would specify only the file’s logical unit number and the parameters to change.

2.1.2.3 Preconnected or Implicitly Named Units

Three unit numbers are automatically associated with specific standard I/O files at the start of program execution. These preconnected units are standard input, standard output, and standard error:

• Standard input is logical unit 5

• Standard output is logical unit 6

• Standard error is logical unit 0

Typically, standard input receives input from the workstation keyboard; standard output and standard error display output on the workstation screen.

In all other cases where a logical unit number but no FILE= name is specified on an OPEN statement, a file is opened with a name of the form fort.n, where n is the logical unit number.