Editing Library Reference (section)

==Functions from the C library==
Functions from the C library for which an interface has been defined at the end of <tt>RSFSRC/api/f90/fortran.c</tt> can be called directly from Madagascar F90 programs. The programmer must know, however, that '''an argument type mismatch will result in a silent failure, with no informative errors.''' There may be other sources of problems as well. Caution therefore must be advised when calling these functions. The reason for these issues is that [http://people.scs.fsu.edu/~burkardt/f_src/mixed/mixed.html if a FORTRAN90 routine needs to pass a scalar parameter to a C routine, there is no standard way to ensure that a value is passed rather than an address]. The success rate of calling C from Fortran [http://w3.pppl.gov/~dmccune/papers-reports/linux_f90.txt is compiler-dependent] and [http://www.cs.sandia.gov/Zoltan/ug_html/ug_fortran.html special types may have to be defined for portability]. If you do have to call a C function from F90, follow the examples of the functions below. Use the C library reference to find argument and output types. A C-to-F90 data type dictionary follows:
{| class="wikitable" align="center" cellspacing="0" border="1"
! style="background:#ffdead;" | C ||! style="background:#ffdead;" | F90
|-
| RSFFILE || type(file)
|-
| INT || integer
|-
| OFFSETT || integer(kind=OFFKIND)
|}
===Void-output functions callable as subroutines===
These can be treated as subroutines, and accessed with a <tt>call</tt> statement. Follow 
* <tt>sf_error</tt> ('''G''') 
* <tt>sf_init</tt> ('''G''') ('''''Can it also be called in subroutines if we want to isolate I/O operations there?''''')
* <tt>sf_seek</tt>

===Non-void-output functions===
It is a good idea to declare in your program the function output type and use the keyword <tt>external</tt>, i.e.:
<pre>real, external :: sf_dosomething</pre>
Alternately, you may define a F90 <tt>interface</tt> block for the procedure(s). 

Several examples can be found in <tt>RSFSRC/filt/lib/rsf.f90</tt>, but they are not enumerated here because F90 wrappers exist for them and they should be used instead of the direct calls to the C library functions.