Input and Output With Portability Routines

The portability library contains routines that change file properties, read and write characters and buffers, and change the offset position in a file. These input and output routines can be used with standard Fortran input or output statements such as READ or WRITE on the same files, provided that you take into account the following:

When used with direct files, after an FSEEK, GETC, or PUTC operation, the record number is the number of the next whole record. Any subsequent normal Fortran I/O to that unit occurs at the next whole record. For example, if you seek to absolute location 1 of a file whose record length is 10, the NEXTREC returned by an inquire would be 2. If you seek to absolute location 10, NEXTREC would still return 2.
On units with CARRIAGECONTROL='FORTRAN' (the default), PUTC and FPUTC characters are treated as carriage control characters if they appear in column 1.
On sequentially formatted units, the C string "\n"c, which represents the carriage return/line feed escape sequence, is written as CHAR(13) (carriage return) and CHAR(10) (line feed), instead of just line feed, or CHAR(10). On input, the sequence 13 followed by 10 is returned as just 10. (The length of character string "\n"c is 1 character, whose ASCII value, indicated by ICHAR('\n'c), is 10.)
Reading and writing is in a raw form for direct files. Separators between records can be read and overwritten. Therefore, be careful if you continue using the file as a direct file.

I/O errors arising from the use of these routines result in a Visual Fortran run-time error.

Portability Routine	Description
ACCESS	Checks a file for accessibility according to mode
CHMOD	Changes file attributes
FGETC	Reads a character from an external unit
FLUSH	Flushes the buffer for an external unit to its associated file
FPUTC	Writes a character to an external unit
FSEEK	Repositions a file on an external unit
FTELL	Returns the offset, in bytes, from the beginning of the file
GETC	Reads a character from unit 5
PUTC	Writes a character to unit 6

All path names can include drive specifications, forward slashes, or backslashes.

Some portability file I/O routines have equivalents in standard Fortran 95/90. For example, you could use the ACCESS function to check a file specified by name for accessibility according to mode. It tests a file for read, write, or execute permission, as well as checking to see if the file exists. It works on the file attributes as they exist on disk, not as a program's OPEN statement specifies them.

Instead of ACCESS, you can use the INQUIRE statement with the ACTION parameter to check for similar information. (The ACCESS function always returns 0 for read permission on FAT files, meaning that all files have read permission.)