Lines

(Corresponds to Section 3.2 of ANSI X3.9-1978 FORTRAN 77.)

The way a Fortran compiler views source files depends entirely on the implementation choices made for the compiler, since those choices are explicitly left to the implementation by the published Fortran standards.

The GNU Fortran language mandates a view applicable to UNIX-like text files--files that are made up of an arbitrary number of lines, each with an arbitrary number of characters (sometimes called stream-based files).

This view does not apply to types of files that are specified as having a particular number of characters on every single line (sometimes referred to as record-based files).

Because a "line in a program unit is a sequence of 72 characters", to quote X3.9-1978, the GNU Fortran language specifies that a stream-based text file is translated to GNU Fortran lines as follows:

• A newline in the file is the character that represents the end of a line of text to the underlying system. For example, on ASCII-based systems, a newline is the <NL> character, which has ASCII value 10 (decimal).
• Each newline in the file serves to end the line of text that precedes it (and that does not contain a newline).
• The end-of-file marker (EOF) also serves to end the line of text that precedes it (and that does not contain a newline).
• Any line of text that is shorter than 72 characters is padded to that length with spaces (called "blanks" in the standard).
• Any line of text that is longer than 72 characters is truncated to that length, but the truncated remainder must consist entirely of spaces.
• Characters other than newline and the GNU Fortran character set are invalid.

For the purposes of the remainder of this description of the GNU Fortran language, the translation described above has already taken place, unless otherwise specified.

The result of the above translation is that the source file appears, in terms of the remainder of this description of the GNU Fortran language, as if it had an arbitrary number of 72-character lines, each character being among the GNU Fortran character set.

For example, if the source file itself has two newlines in a row, the second newline becomes, after the above translation, a single line containing 72 spaces.