Lines and source formats
A line is a horizontal arrangement of characters. A column is a vertical arrangement of characters, where each character, or each byte of a multibyte character, in a given column shares the same horizontal line position.
Because XL Fortran measures
lines in bytes, these definitions apply only to lines containing single-byte
characters. Each byte of a multibyte character occupies one column. 
| Initial line | Is the first line of a statement. |
| Continuation line | Continues a statement beyond its initial line. |
| Comment line | Does not affect the executable program and can be used for
documentation. The comment text continues to the end of a line. Although
comment lines can follow one another, a comment line cannot be continued.
A line of all white space or a zero-length line is a comment line
without any text. Comment text can contain any characters allowed
in a character context. If an initial line or continuation line is not continued, or if it is continued but not in a character context, an inline comment can be placed on the same line, to the right of any statement label, statement text, and continuation character that may be present. An exclamation mark (!) begins an inline comment. |
| Conditional compilation line | Indicates that the line should only be compiled if recognition of conditional compilation lines is enabled. A conditional compilation sentinel should appear on a conditional compilation line. For more information, see Conditional compilation. |
| Debug Line | Indicates that the line is for debugging code (for fixed source form only). In XL Fortran the letter D or X must be specified in column 1. For more information, see Debug lines. |
| Directive line | Provides instructions or information to the compiler in XL Fortran. For more information, see Comment form directives. |
In XL Fortran source lines can be in fixed source
form or free source form format. Use the SOURCEFORM directive
to mix source formats within the same program unit. When
you use the f77 or fort77 invocation
command, fixed source form is the default. When you use xlf or xlf_r to
compile the .f, .F, .f77, or .F77 files, fixed source form is also
the default. When you use the xlf90, xlf90_r, xlf95, xlf95_r, xlf2003, xlf2003_r, xlf2008, xlf2008_r,
or 
xlcuf
invocation command, Fortran 90 free source form is the
default.
See Compiling XL Fortran Programs in the XL Fortran Compiler Reference for details on invocation commands.
