View source for FAQ/Programming

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[[Category:FAQSection]]

== FAQ Section [[faqnumber::7]]: [[faqname::Programming]] ==
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[[faqdescription::Questions about writing applications and solvers]]
=== Compiling ===

==== Where does <tt>wmake</tt> get the values for the environmental variables from? ====

All <tt>wmake</tt> variables come from (in this order)

# <tt>$WM_DIR/rules/General/general</tt>
# <tt>$WM_DIR/rules/${WM_ARCH}${WM_COMPILER}/general</tt>
# <tt>$WM_DIR/rules/${WM_ARCH}/c++</tt>

(Source: [http://openfoam.cfd-online.com/forum/messages/1/546.html])

For a complete list of foam related environment variables, see [[Environment_variables]].

==== What does "-lOpenFOAM" and '-lfiniteVolume' mean? ====
For example, in the file {{tt|src/finiteVolume/Make/options}} is the following content:
<code>EXE_INC = \
    -I$(LIB_SRC)/triSurface/lnInclude \
    -I$(LIB_SRC)/meshTools/lnInclude \

LIB_LIBS = \
    -lOpenFOAM \
    -ltriSurface \
    -lmeshTools
</code>
The last 3 lines refer to the libraries {{tt|OpenFOAM}}, {{tt|triSurface}} and {{tt|meshTools}}:
* On Linux, this equates to the respective 3 files: {{tt|libOpenFOAM.so}}, {{tt|libtriSurface.so}} and {{tt|libmeshTools.so}}
* On Mac OS X, this equates to the respective 3 files: {{tt|libOpenFOAM.dylib}}, {{tt|libtriSurface.dylib}} and {{tt|libmeshTools.dylib}}
* On Window, this equates to the respective 3 files, although there are two variants of files:
** The interface files: {{tt|libOpenFOAM.a}}, {{tt|libtriSurface.a}} and {{tt|libmeshTools.a}} - these are always needed for building on Windows with GCC.
** The actual binary library files, i.e. the ones used for running OpenFOAM: {{tt|libOpenFOAM.dll}}, {{tt|libtriSurface.dll}} and {{tt|libmeshTools.dll}}

For a lot mode details about this, read: [http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html 3. Shared Libraries] chapter at [http://tldp.org tldp.org]

=== Working with fields ===

==== How to calculate the field value of an arbitrary point? ====

See [[snip_calculate_field_value_at_point|Calculating the field value at an arbitrary point]].

=== OpenFOAM's template library ===

==== What is the object registry? ====
See [[snip_objectRegistry|objectRegistry explained]].

==== What do the filenames mean? ====
OpenFOAM's file naming convention.  For <tt>exampleClass</tt>, these filenames may exist:

* <tt>exampleClass'''.H</tt>''' - Main header.
* <tt>exampleClass'''.C</tt>''' - Main body.
* <tt>exampleClass'''Fwd.H</tt>''' - Forward declarations.
* <tt>exampleClass'''I.H</tt>''' - Inline functions implemented.
* <tt>exampleClass'''IO.C</tt>''' - IO functions implemented.
* <tt>exampleClass'''M.H</tt>''' - Macros.
* <tt>exampleClass'''FunctionName.C</tt>''' - <tt>FunctionName</tt>'s implementation (seperated for no other reason than aesthetics).

There may be others as well.  Unknown naming conventions:

* <tt>exampleClass'''s.H</tt>''' 
* <tt>exampleClass'''s.C</tt>'''

Some filenames add an '''<tt>s</tt>''' to the end.  These may be associated with <tt>static</tt> variables / functions.  They may also be associated with the <tt>NoRepository</tt> flag.

==== What is tmp<>? ====
See [[snip_tmp_explained|tmp explained]].

==== What is runtime selection? ====
See [[snip_runtime_selection_mechanism|Runtime selection mechanism]].

=== Adding new features ===

==== How do I add a new wall-function? ====

See the How-To: [[HowTo_Adding_a_new_wall_function|Adding a new wall-function]].

==== How do I add a new boundary condition? ====

See the How-To: [[HowTo_Adding_a_new_boundary_condition|Adding a new boundary condition]].

=== Frequently occurring issues ===

==== <tt>error: call of overloaded ‘sqrt(double)’ is ambiguous</tt> ====
For example, if you use a piece of code like this one:
<cpp>volScalarField strainRate = sqrt(2.0)*mag(symm(fvc::grad(U)));</cpp>

you're likely to get this error message:
<pre>error: call of overloaded ‘sqrt(double)’ is ambiguous
</pre>

Possible solutions, instead of simply using <tt>sqrt(2.0)</tt>:
<cpp>::sqrt(2.0)
scalar(::sqrt(2.0))
::sqrt(scalar(2.0))
</cpp>

The reason for this is that OpenFOAM has got several function overloads for {{tt|sqrt}} for dealing with fields, but it does not overload the original function {{tt|sqrt}}, which leads to the compiler getting confused with which overload it should uses.

For more details, please refer to posts #10 and #11 on this thread: [http://www.cfd-online.com/Forums/openfoam-programming-development/146061-adding-strainrate-solver.html#post526653 adding strainRate in a solver]
Faqdescription	Questions about writing applications and solvers +
Faqname	Programming +
Faqnumber	7 +