R help - Nov 2006 - Error in Calling C++ function from R!!!

Hello, 

I tried to call an external function of R from the following code in C++: 

void prodgdot(double *x, double *y, int *n, double *output) 

{ 

	int i; 

	*output=0; 

	for (i=0;i<*n;i++) 

		{ 

		*output+=x[i]*y[i]; 

		} 

} 

I compiled it using from my working directory in linux terminal and I think 
it's ok: 

giba at giba-desktop:~/mysrc/meus_testes_iniciais$ R CMD SHLIB codigoprova.cc 
# The output 
g++ -I/usr/share/R/include -I/usr/share/R/include      -fpic  -g -O2 -c 
codigoprova.cc -o codigoprova.o 
g++ -shared  -o codigoprova.so codigoprova.o   -L/usr/lib/R/lib -lR 

After, I tried to call R from my working directory an Error occurs: 
> x<-c(1,4,6,2) 
> y<-c(3,2.4,1,9) 
> dyn.load("codigoprova.so") 
> is.loaded("codigoprova.so") 
[1] FALSE 
>
product<-.C("prodgdot",myx=x,muy=y,myn=NROW(x),myoutput=as.double(0))
Error in .C("prodgdot", myx = x, muy = y, myn = NROW(x), myoutput = 
as.double(0)) : 
        C symbol name "prodgdot" not in load table
> 
Does anyone know what is the problem? 

Thank's in advance! 
Gilberto.

>>product<-.C("prodgdot",myx=x,muy=y,myn=NROW(x),myoutput=as.double(0))
> 
> Error in .C("prodgdot", myx = x, muy = y, myn = NROW(x), myoutput
=
> as.double(0)) : 
>         C symbol name "prodgdot" not in load table 
> 
> 
> Does anyone know what is the problem? 
  C++ name mangling?

http://cran.r-project.org/doc/manuals/R-exts.html#Interfacing-C_002b_002b-code

  Solution: wrap in extern "C" { ... } as discussed there.

Barry