4.1.3 Tab Form

The f95 fixed-format source text is defined as follows:

• A tab in any of columns 1 through 6 makes the line as a tab form source line.

• A comment indicator or a statement number may precede the tab.

• If a tab is the first nonblank character, then:

  • If the character after the tab is anything other than a nonzero digit, then the text following the tab is an initial line.

  • If there is a nonzero digit after the first tab, the line is a continuation line. The text following the nonzero digit is the next part of the statement.

The f95 default maximum line length is 72 columns for fixed form and 132 for free form. Use the -e compiler option to extend the lines in fixed-format source to 132 columns.

Example: The tab form source on the left is treated as shown on the right.

!^IUses of tabs
^ICHARACTER *3 A = ’A’
^IINTEGER B = 2
^IREAL C = 3.0
^IWRITE(*,9) A, B, C
9^IFORMAT(1X, A3,
^I1 I3,
^I2 F9.1 )
^IEND

!       Uses of tabs
        CHARACTER *3 A = ’A’
        INTEGER B = 2
        REAL C = 3.0
        WRITE(*,9) A, B, C
9       FORMAT(1X, A3,
       1 I3,
       2 F9.1 )
        END

In the example above, ”^I” stands for the tab character, and the line starting with “1” and “2” are continuation lines. The coding is shown to illustrate various tab situations, and not to advocate any one style.

Tabs in f95 force the rest of the line to be padded out to column 72. This may cause unexpected results if the tab appears within a character string that is continued onto the next line:

Source file:

^Iprint *, "Tab on next line
^I1this  continuation line starts with a tab."
^Iend

Running the code:

Tab on next line                                             this  continuation
 line starts with a tab.

When tab formatting is used with the —f77 option, there is no 132 character limit to the line length. The line can be much longer.