D Compile Options

One standard debugging technique is to print out the values of variables and constants from different parts of your program to check that they are being transferred correctly. Another debugging technique is to build a simple test case right into your program and then to check that it continues to give a known answer even after you make those ``harmless'' modifications. Once these debugging structures are built into your program, you just leave them there permanently-without having to execute them. You do that by commenting them out with a d or D in column 1. For example:
   

 
subroutine sub1   	   
    	   
d  write(6,999) 'at 999, x, y =', x, y   	d in col. 1.   
d 999 format( (a), 2f10.3)   	d in col. 1.   

If this is done with the traditional C in column 1, you must go back and modify the source code to uncomment them. With a d in column 1 you uncomment these statements by invoking the D (for debugging) option of the Fortran compiler:

% f77 -D sub1.f   	Option makes D statements =  source.   

Or alternatively, you may place debug directives in the source file:

 
$debug on   	Treat D statements as source.   
$debug off   	Treat D statements as comments.