R help - Jun 2004 - help in R calling C function

Hi there,

I want to call a C function in R. I have some experience on it, but this 
time I need to call another C function in the "main" C function. As a 
simple example, I use the following C code:

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>


void main(double *alpha)
{
	double test();
	double beta;
	beta= *alpha *2 + test(*alpha);
}

double test(double *alpha)
{
	double value;
	value = *alpha *3;
	return(value);
}

I used "gcc -c main.c" and "Rcmd SHLIB main.o" and I got the
main.dll file.
In R I use the following code to call the C function "main":

dyn.load("c:/Program Files/R/rw1060/bin/main.dll")
a=4.2
b=.C('main', as.double(a))

But the R system crashed. I know I can only define the function type in C 
as "void" to be called by R. But what if I want to call another C
function
in the "main" C function? Thank you for your help!

Sincerely,

Lei Liu

Lei Liu wrote:
> Hi there,
> 
> I want to call a C function in R. I have some experience on it, but this 
> time I need to call another C function in the "main" C function.
As a
> simple example, I use the following C code:
> 
> #include <stdio.h>
> #include <math.h>
> #include <stdlib.h>
> #include <time.h>
> 
> 
> void main(double *alpha)
1. don't call it "main".
2. alpha must not be a pointer.

> {
>     double test();
>     double beta;
>     beta= *alpha *2 + test(*alpha);
> }
>
> double test(double *alpha)
> {
>     double value;
>     value = *alpha *3;
>     return(value);
> }
> 
> I used "gcc -c main.c" and "Rcmd SHLIB main.o" and I
got the main.dll
> file. In R I use the following code to call the C function
"main":
3. "Rcmd SHLIB main" is sufficient.

> dyn.load("c:/Program Files/R/rw1060/bin/main.dll")
4. Why do you compile in R's /bin directory? That's not necessary,
it's
rather confusing.

Uwe Ligges
> a=4.2
> b=.C('main', as.double(a))
>
> But the R system crashed. I know I can only define the function type in 
> C as "void" to be called by R. But what if I want to call another
C
> function in the "main" C function? Thank you for your help!
> 
> Sincerely,
> 
> Lei Liu
> 
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