Help Files: Fortran77: Debugging

     HELP                      Sep. 15, 1984             F77/DEBUGGING



                      Debugging Aids for F77 Programs

     The first step in debugging is to understand  the  error  message
     you are getting.  See "help f77 error_msgs" for advice on that.

     There are several utilities that can be used  in  debugging.   If
     you  have a core dump, use the debugger, dbx, to look at the core
     dump.  If you compiled and loaded with the -g flag,  dbx  can  be
     used to tell the line at which your program failed and to display
     the values of variables.  Dbx can also be used to monitor a  pro-
     gram while running and do interactive debugging.

     If you did not compile with the -g flag but did load using the -g
     flag,  dbx  will  still tell you which subroutines were active at
     the time of the failure.  If you did not load with the  -g  flag,
     dbx can not be used at all.  See "help f77 dbx" and "man dbx" for
     more information.

     If you might be exceeding the bounds of an  array,  you  can  use
     f77's -C flag to check for subscripts out of range.

     The 'nm' utility is useful in telling which procedures are refer-
     enced  in  which  .o  files.  Thus if the loader issues a message
     like:

             Undefined:
             _subr_

     and you don't know where subr() is called, the command:

             nm -og *.o | grep subr

     will tell you  which  '.o'  files  in  this  directory  reference
     subr().

     The -M flag can be used to tell out of which archive or library a
     .o file is loaded.