GRASS GIS Debugging:

See also
https://grasswiki.osgeo.org/wiki/GRASS_Debugging

----------------------------------------------------
At user level:

 Print debugging message if variable DEBUG
 is set to level equal or greater

g.gisenv set="DEBUG=3"

Levels: (recommended levels)
 * 0 - silence
 * 1 - message is printed once or few times per module
 * 3 - each row (raster) or line (vector)
 * 5 - each cell (raster) or point (vector)

Further hints:
> How can I force gcc, to complain about missing header file?
 
'-Wimplicit-function-declaration'
'-Werror-implicit-function-declaration'
     Give a warning (or error) whenever a function is used before being
     declared.
----------------------------------------------------

To make gcc less tolerant in accepting errors and code flaws, compile
with (see also the INSTALL.md file):

export CFLAGS='-g -ansi -Wall -D_BSD_SOURCE=1 -D_SVID_SOURCE=1 -D_POSIX_SOURCE=1 -D_POSIX_C_SOURCE=199506L'

Also nice to emulate gcc/MacOSX compiler:
CFLAGS='-fno-common'

It is a good idea to use '-Wall -Werror' as gcc options. This means
it treats the warnings as errors, i.e. it stops on them. So you have time
to read them then.

The gcc switch -Wimplicit-function-declaration (implied by -Wall) should
report missing prototypes (use -Werror-implicit-function-declaration to
make it an error rather than a warning).
 
The linker switch --warn-common (e.g. LDFLAGS='-Wl,--warn-common') might
be useful for catching multiply-defined symbols.

Be sure to compile using debug flags (gcc -g) and don't "strip" the
binaries after compiling.
----------------------------------------------------
C Code debugging Software:


1) Debugger (command-line)
      gdb `which r.plane`
      r <flags> <parameters>
      bt full


   To debug in a running process, find out the process ID (PID)
      ps -aef
   and then use
      gdb --pid=PID

   to attach to running process PID. It will stop, enter 'c'
   to continue and so forth (bt full for backtrace).

2a) Graphical front-end for command-line debugger: ddd
      ddd `which r.plane`
      RUN -> here enter Parameters/Flags
    
      http://www.gnu.org/software/ddd/
       (GNU DDD is a graphical front-end for command-line debuggers such as
        GDB, DBX, WDB, Ladebug, JDB, XDB, the Perl debugger, the bash debugger, or the
        Python debugger. )

    See mini tutorial here:
    https://grasswiki.osgeo.org/wiki/GRASS_Debugging

2b) Graphical front-end for command-line debugger: kdbg
      Use the menus

----------------------------------------------------
Debugging on Mac OS X

 The 'ldd' command doesn't exist, but
  otool -L 
 does almost the same job.

----------------------------------------------------
Using valgrind to find memory leaks (http://valgrind.org/):

* Memory note for vector modules:
   Support structures are not released by default because it take long time
   and it is much faster if it is done by system.

   You have to call Vect_set_release_support() before
   Vect_close() if you want to use valgrind.

* Example (see also http://bambi.otago.ac.nz/hamish/grass/memleak/v.in.ascii/):

    CMD="v.in.ascii -zt z=3 in=lidaratm2_250k.txt out=lidaratm2_250k fs=,"
    valgrind -v --tool=addrcheck --leak-check=yes --show-reachable=yes $CMD --o

* On 64bit boxed valgrind is not supported. An alternative is 'memusage':

     memusage -t -T v.in.ogr -o dsn=clcit2000 layer=LAB,ARC \
                             type=centroid,boundary output=corine2000_it

----------------------------------------------------
Profiling GRASS with GCC:

Profiling allows the compiler to insert code that collects various 
statistics for later analysis.  Profiling with GCC is particularly 
useful for quickly locating bottleneck functions, determining how 
much time is spent in a particular function, and how many times that 
function was called.

To profile the entire GRASS package, the following steps should be 
followed for success:

 * Before running 'configure', both the CFLAGS and LDFLAGS environment 
   variables need to be altered by adding the -pg flag to enable 
   profiling. This can be accomplished by the following:

   CFLAGS='-pg' LDFLAGS='-pg' ./configure ...

   CFLAGS and LINK_FLAGS in include/Make/Platform.make can be manually 
   edited after running 'configure', also.

 * 'configure' must be called with --disable-shared if you intend to 
   profile GRASS libraries (recommended)

 * make GRASS as normal

 * In order to run GRASS without errors, lib/init must be recompiled 
   without linking using the -pg flag.  Edit include/Make/Platform.make 
   and remove -pg from LINK_FLAGS.  'cd lib/init; make clean; make'.  
   GRASS can now be installed as normal.

When running a GRASS C module, a file called gmon.out is created when 
the module completes execution.  This file can be analyzed with 
the GCC tool 'gprof'.

Note that when 'make distclean' is run, the manual changes to 
include/Make/Platform.make are also removed.

