These files need not exist before program execution.
n is referenced, where n is the logical unit number (except for 0, 5, and 6, which have special meaning). If the first operation on a logical unit is an I/O statement other than OPEN or INQUIRE, the file fort. Use of the OPEN statement is optional in those cases where default conventions can be assumed. n, where n is the logical unit number.Ģ.1.3 Opening Files Without an OPEN Statement 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. Typically, standard input receives input from the workstation keyboard standard output and standard error display output on the workstation screen. These preconnected units are standard input, standard output, and standard error: Three unit numbers are automatically associated with specific standard I/O files at the start of program execution. In this case, you would specify only the file's logical unit number and the parameters to change.Ģ.1.2.3 Preconnected or Implicitly Named Units 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. When compiling in FORTRAN 77 compatibility mode ( -f77), you can specify STATUS='KEEP' in the CLOSE statement to preserve the scratch file. This file is deleted upon termination of the program or execution of a CLOSE statement. Specifying STATUS='SCRATCH' in the OPEN statement opens a file with a name of the form tmp.F AAAxnnnnn, 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. The OPEN statement need not specify a name the runtime system supplies a file name according to several conventions. See man page entries for getarg(3F), getcwd(3F), and getenv(3F) for details these and other useful library routines are also described in the Fortran Library Reference. These routines are further described in Section 2.1.4, Passing File Names to Programs. Getfil PATH IS: /home/users/auser/subdir/atest.f The program uses the library routines GETENV, LNBLNK, and GETCWD to return the value of the $HOME environment variable, find the last non-blank in the string, and determine the current working directory:ĭemo% f95 -o getfil GetFilNam.f demo% getfil ENTER FILE NAME: The following example ( GetFilNam.f) shows one way to construct an absolute path file name from a typed-in name. Library routines can be used to bring command-line arguments and environment variables into the program as character variables for use as file names in OPEN statements. Also, the specifier may be a character constant, variable, or character expression. The FILE= specifier on an OPEN statement may specify a simple file name ( FILE='myfile.out') or a file name preceded by an absolute or relative directory path ( FILE='./Amber/Qproj/myfile.out'). This file can be pre-existing or created by the program.
The OPEN statement's FILE= specifier establishes the association of a logical unit to a named, physical file at runtime. Also, certain preconnected units are automatically associated with specific files at the start of program execution. The asterisk stands for standard input file when it appears in a READ statement it stands for standard output file when it appears in a WRITE or PRINT statement.Ī Fortran logical unit can be associated with a specific, named file through the OPEN statement. The character * can appear as a logical unit identifier. Logical units are identified in an I/O statement by a logical unit number, a nonnegative integer from 0 to the maximum 4-byte integer value (2,147,483,647). 2.1 Accessing Files From Within Fortran Programsĭata is transferred between the program and devices or files through a Fortran logical unit.
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