Using Fix and Continue With Runtime Checking

You can use runtime checking along with fix and continue to isolate and fix programming errors rapidly. Fix and continue provides a powerful combination that can save you a lot of debugging time. Here is an example:.

% cat -n bug.c
     1 #include stdio.h
     2 char *s = NULL;
     3
     4 void
     5 problem()
     6 {
     7      *s = ’c’;
     8 }
     9
    10 main()
    11 {
    12      problem();
    13      return 0;
    14 }
% cat -n bug-fixed.c
     1 #include stdio.h
     2 char *s = NULL;
     3
     4 void
     5 problem()
     6 {
     7
     8      s = (char *)malloc(1);
     9      *s = ’c’;
    10 }
    11
    12 main()
    13 {
    14      problem();
    15      return 0;
    16 }
yourmachine46: cc -g bug.c
yourmachine47: dbx -C a.out
Reading symbolic information for a.out
Reading symbolic information for rtld /usr/lib/ld.so.1
Reading symbolic information for librtc.so
Reading symbolic information for libc.so.1
Reading symbolic information for libintl.so.1
Reading symbolic information for libdl.so.1
Reading symbolic information for libw.so.1
(dbx) check -access
access checking - ON
(dbx) run
Running: a.out
(process id 15052)
Enabling Error Checking... done
Write to unallocated (wua):
Attempting to write 1 byte through NULL pointer
Current function is problem
    7       *s = ’c’;
(dbx) pop
stopped in main at line 12 in file "bug.c"
   12       problem();
(dbx) #at this time we would edit the file; in this example just copy  
the correct version
(dbx) cp bug-fixed.c bug.c
(dbx) fix
fixing "bug.c" ......
pc moved to "bug.c":14
stopped in main at line 14 in file "bug.c"
   14       problem();
(dbx) cont

execution completed, exit code is 0
(dbx) quit
The following modules in \Qa.out’ have been changed (fixed):
bug.c
Remember to remake program.

For more information on using fix and continue, see Memory Leak (mel) Error.