accessing a printf-like function from scheme

accessing a printf-like function from scheme

[Dan McMahill]

Hello,

I'm trying to provide scheme access to a C function which has the same 
interface a printf(). What I'd like to do in scheme is something like

(gschem-log
    "This is a %s message with %d args, pi is %g\n"
    "log"
    3
    3.14
)

so I've gotten as far as a function which takes a variable number of 
arguments and made it available from scheme but can't seem to figure out 
the last step which is how to get the elements from the :

SCM g_funcs_log(SCM s_num_list)
{
   SCM s_element;
   int length;
   int i;

   /* Check that the input is a list */
   SCM_ASSERT (SCM_NFALSEP (scm_list_p (s_num_list)),
	      s_num_list,
	      SCM_ARG1,
	      "gschem-log");
   length = scm_num2int(scm_length(s_num_list), 0, "g_funcs_log()");

   if (length == 0)
      return SCM_BOOL_T;

   /* how to actully feed the data to s_log_message which
    * has a printf-like interface
    */
   s_log_message ("Hi there.  Length = %d\n", length);

   return SCM_BOOL_T;
}

scm_c_define_gsubr ("gschem-log", 0, 0, 1, g_funcs_log);



If it would be easier I can also write a

void s_log_messagev (const char * restrict format, va_list ap);

to complement the

void s_log_message(const char * restrict format, ...);

I tried to find some sort of scm_list2_c_va_list() but haven't found it yet.

Any suggestions?

Thanks
-Dan





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Re: accessing a printf-like function from scheme

[Tomas Zerolo]

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On Tue, Apr 25, 2006 at 08:44:55AM -0400, Dan McMahill wrote:
> 
> Hello,
> 
> I'm trying to provide scheme access to a C function which has the same 
> interface a printf(). [...]

> SCM g_funcs_log(SCM s_num_list)
> {
>   SCM s_element;
>   int length;
>   int i;
> 
>   /* Check that the input is a list */
>   SCM_ASSERT (SCM_NFALSEP (scm_list_p (s_num_list)),
> 	      s_num_list,
> 	      SCM_ARG1,
> 	      "gschem-log");
>   length = scm_num2int(scm_length(s_num_list), 0, "g_funcs_log()");
> 
>   if (length == 0)
>      return SCM_BOOL_T;
> 
>   /* how to actully feed the data to s_log_message which
>    * has a printf-like interface
>    */
>   s_log_message ("Hi there.  Length = %d\n", length);
> 
>   return SCM_BOOL_T;
> }

I fear there is no portable way for this...

> If it would be easier I can also write a
> 
> void s_log_messagev (const char * restrict format, va_list ap);
> 
> to complement the
> 
> void s_log_message(const char * restrict format, ...);
> 
> I tried to find some sort of scm_list2_c_va_list() but haven't found it yet.
> 
> Any suggestions?

I'm not aware of a portable way of putting together a va_list (just of
taking it apart). And I wouldn't expect to see one -- C compilers do a
lot of obscure stuff to optimize parameter passing.

Maybe your function needs another interface (e.g. an array of params)?

Regards
-- tomás

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Re: accessing a printf-like function from scheme

[William Xu]

Dan McMahill <mcmahill@mtl.mit.edu> writes:

> I'm trying to provide scheme access to a C function which has the same
> interface a printf(). What I'd like to do in scheme is something like

But, doesn't SLIB already have this? 

(info "(slib) Standard Formatted Output")

-- 
William


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