7 option for cc

[P]

     I work in a 4.2 BSD environment with brl "enhancements".  What this means
is we have access to system V commands and libraries but not to system V
system calls.  On one of the programs I was writing I had the following code:

#include <stdio.h>
.
.
.
.
writeda()
{
	FILE *fopen(), *daction;

	if ((daction = fopen(file,"w"))== NULL){
		fprintf(stderr,"ERROR: Could not create %s\n",file);
		perror("");
	}

	/*  Writes out actual file               */
	fprintf(daction,"                              R & A\n");

.
.
.
	fclose(daction);
}

   I compiled (maked) using the the -O flag (cc -O progname), when I ran the
program that got to the first fprintf statement I got memory fault - core
dump.  After extensive checking of the program for bugs I gave up. I then
ported it over to s System V machine and it worked with no problems.  I then
read the manual page on cc and  read about the -7 option:



     -7      Compile using a 4.2BSD environment (a UNIX System V
             environment is the default.)

AFter recompilng with the -O7 flags I got it to run and have had no problems
since.  The question I have is does the -7 option really do that much? What
does it do?  Could the error be me or the compiler option.  I had never used
-7 before.  I have had no problems with prior programs.

   ..Dennis