Path: utzoo!mnetor!uunet!husc6!bbn!gatech!stratus!strick
From: strick@stratus.UUCP (henry strickland)
Newsgroups: comp.lang.c++
Subject: Re: C++ debugging?
Message-ID: <1037@stratus.UUCP>
Date: 12 Feb 88 19:45:16 GMT
References: <41938@ti-csl.CSNET> <10053@ulysses.homer.nj.att.com>
Reply-To: strick@stratus.UUCP (henry strickland)
Organization: the clouds project -- computer science -- georgia tech
Lines: 190

In article <41938@ti-csl.CSNET> ramey@ti-csl.UUCP (Joe Ramey) writes:
>(I'm sure this question has been asked before, so perhaps someone with
>a summary could forward it to me.)  How well does dbx debug C++ code?

I'm answering a different question:  How do I use dbx to debug C++ code?

(using AT&T's current release of C++, i.e. CC, cfront and munch):

My preference is to keep the C intermediate file (*..c), and debug with
respect to it.  I prefer to have the line numbers used by dbx be the
C line numbers. The C intermediate will then tell what line of
the C++ source generated it.    With X windows, I can keep 1) the C++
sources, 2) the C intermediates, and 3) my dbx session all on the screen.
Without a native C++ debugger, the C intermediate is a necessary
evil because of the modified variable names, baroque-looking (but
beautifully straightforward in execution) code generated by inlines,
etc.   

To do this, I edit the "CC" shell script to send the output of "cfront",
which is the C intermediate, through a filter to convert the 
	#line "filename" lineno
lines into C comments
	/* #line "filename" lineno */
so that dbx will refer to the raw intermediate-C line number, 
yet in these comments I can find the corresponding C++ line numbers.


The following lex script will do this: 
( however, "sed" is too dangerous -- it mangles long lines.  )

==================================================================
%%
^[#].*$		printf("\t\t/* %s */", yytext );
==================================================================


However, while I'm at it, I'll tell you what I really do.

I name my C++ sources ".x", a contraction of the proposed ".cxx".
I name my C intermediates ".i", a convention the sun C compiler understands.
Now nothing interferes with normal ".c" files.

Then I put the following rules in my makefile, and avoid the expense
of running the CC script.   Don't forget to "ld" with "-lC".

==================================================================

.SUFFIXES:	.o .i .x .s .c

CXXI=/usr/include/CC/


.x.i: 
	/lib/cpp -C -I$(CXXI) $*.x | cfront | line2com $*.i

.x.o:
	/lib/cpp -C -I$(CXXI) $*.x | cfront | line2com $*.i
	/bin/cc $(CFLAGS) -c $*.i

==================================================================

The following C program is used for "line2com",  rather than the
lex script I presented above.  It does basically the same thing,
but it is a bit more robust, in that it removes the $*.i file
in the case that "cfront" terminates with a nonzero status, or
in the case that it dies from a signal (such as the user's SIGINT).
This is necessary so that "make" knows it must recompile.


==================================================================

/*
 *   line2com:    change "#" lines into C comments
 * 
 *   Henry Strickland  -- Georgia Tech Computer Science (clouds project)
 *
 *   <strick@gatech.edu>           (known to work on a sun3 (4.2BSD) )
 *
 *   9jan87 -- rather nasty code for such a simple concept
 *
 *	usage:     line2com [outname]
 *
 *   reads standard input, makes "#line" lines into comments,
 *	and writes to [outname] or to standard output.
 *
 *   waits on any children (preprocessors, such as cfront,
 *	in a pipe chain) and exits bad if any of them
 *  	exit bad.  If we exit bad, we also unlink [outname],
 *	if any.   THIS IS IMPORTANT IF ONE USES PIPES.
 */



#include <stdio.h>
#include <sys/wait.h>

#define BIG	50000		

char buf[BIG];

int p;   		/* process id returned from wait() */
union wait s;		
int stati;		/* nonzero if any status nonzero */
int retval;		/* exit value */

FILE *output;
char *filename;
char *cmdname;

handler()
{
	if (filename) unlink(filename);
	fprintf(stderr, "%s: KILLED!\n", cmdname );
	exit(250);
};

main(argc,argv)
	char *argv[];
{
	int i;

	/* figure out with what name we were invoked */
	cmdname= argc>0? argv[0] : "line2com";

	/* remove [outfile] if we are killed */ 
	for ( i=1; i<16; i++)
		signal(i,handler);

	/* open the [outfile] or use stdout */
	if ( argc>1 ) {
		filename= argv[1];
		output= fopen( filename, "w" );
		if ( !output ) {
			fprintf(stderr, "%d: ERR: cannot creat: ");
			perror( filename ); exit(1);
		}
	} else {
		output= stdout;
	}

	/* filter stdin to stdout */
	while ( fgets(buf, BIG, stdin ) ) {
		if ( buf[0]=='#' ) {
			/* comment out all # lines */
			fputs( "\t\t\t/*", output);
			buf[strlen(buf)-1]='\0';  /* remove \n */
			fputs( buf, output);
			fputs( "*/\n", output);
		} else {
			/* copy all other lines verbatim */
			fputs( buf, output);
		}
	}


	/* wait for any children.  this _seems_ to work. */
	do { 
		extern errno;
		s.w_status=0;
		p=wait(&s);
		stati |= s.w_status;    /* collect all stati */
		/* fprintf(stderr,"%s: WAIT p%d s%08x e%d\n", cmdname, 
				p, s.w_status, errno ); */
	} while ( p>0 );

	if ( stati ) {
		/* if any one of them had nonzero status */
		/* try to find a decent exit() value */
		retval= 255&( stati + (stati>>8) );
		if (retval==0) retval=255;

		fprintf(stderr,"%s: EXIT(%d) (stati=%08x)\n", 
				cmdname, retval, stati); 
		/* remove [outfile] on errors */
		if ( argc>1 ) unlink( filename );
		exit(retval);
	} else {
		/* fprintf(stderr,"%s: EXIT GOOD\n", cmdname); */
		exit(0);
	}
};

==================================================================


Henry Strickland     <strick@gatech.edu>     gatech!strick   404-676-1313


-- 
Henry Strickland     <strick@gatech.edu>     gatech!strick   404-676-1313