erica@technodyke.com (Erica) wrote:
>
> My basic C program to compute the 2D Fourier transform of a bunch of
> data works fine when I compile it with gcc. However, I would like to
> incorporate that code into a larger program that I wrote with C++.
> Unfortunately, I cannot get my program to compile with g++. 
> 
> I compile it as follows:
> 
> g++ ft2d.c -o ft2d -I/usr/local/include -L /usr/local/lib -lfftw3 -lm
> 
> The errors I get are:
> 
> ft2d.c: In function `int main()':
> ft2d.c:13: invalid conversion from `void*' to `double (*)[2]'
> ft2d.c:14: invalid conversion from `void*' to `double (*)[2]'

IMHO if you want to mix C and C++ in a project, you should
leave your C files as .C files, (and compile them with gcc not g++).
If you include the corresponding .H file from a C++ source file
do this:
  extern "C" {
    #include "ft2d.h"
  };

Alternatively you could write a wrapper file that uses this, 
that would avoid having to do this in every other unit that has
to include the C header.

There's a chapter in the c.l.c++ FAQ about mixing C and C++ in 
projects, have a read of it and see if there is any more advice.

That did the trick...thanks!!

"Howard" <alicebt@hotmail.com> wrote in message news:<DA%1d.594287$Gx4.169205@bgtnsc04-news.ops.worldnet.att.net>...
> "Erica" <erica@technodyke.com> wrote in message
> news:346a55df.0409151004.7edf489e@posting.google.com...
> > Hi,
> >
> > I am currently working on a program using FFTW-> http://www.fftw.org .
> > My basic C program to compute the 2D Fourier transform of a bunch of
> > data works fine when I compile it with gcc. However, I would like to
> > incorporate that code into a larger program that I wrote with C++.
> > Unfortunately, I cannot get my program to compile with g++.
> >
> > I compile it as follows:
> >
> > g++ ft2d.c -o ft2d -I/usr/local/include -L /usr/local/lib -lfftw3 -lm
> >
> > The errors I get are:
> >
> > ft2d.c: In function `int main()':
> > ft2d.c:13: invalid conversion from `void*' to `double (*)[2]'
> > ft2d.c:14: invalid conversion from `void*' to `double (*)[2]'
> >
> 
> You don't note in your code what lines 13 and 14 are, but if I'm counting
> correctly, the errors are on the fftw_malloc lines, right?  You probably
> need to cast the results of those function calls to (fftw_complex *).  It
> appears that the fftw_malloc call returns a void*, and the compiler is
> complaining about that type not matching your in and out variables' declared
> type.
> 
> -Howard
> 
> > Here is my code:
> >
> > #include <fftw3.h>
> > #include <math.h>
> >
> > int main(void)
> > {
> >     fftw_complex *in, *out;
> >     fftw_plan p;
> >     int nx = 5;
> >     int ny = 5;
> >     int i;
> >
> >     /* Allocate the input and output arrays, and create the plan */
> >     in = fftw_malloc(sizeof(fftw_complex) * nx * ny);
> >     out = fftw_malloc(sizeof(fftw_complex) * nx * ny);

"Erica" <erica@technodyke.com> wrote in message
news:346a55df.0409151004.7edf489e@posting.google.com...
> Hi,
>
> I am currently working on a program using FFTW-> http://www.fftw.org .
> My basic C program to compute the 2D Fourier transform of a bunch of
> data works fine when I compile it with gcc. However, I would like to
> incorporate that code into a larger program that I wrote with C++.
> Unfortunately, I cannot get my program to compile with g++.
>
> I compile it as follows:
>
> g++ ft2d.c -o ft2d -I/usr/local/include -L /usr/local/lib -lfftw3 -lm
>
> The errors I get are:
>
> ft2d.c: In function `int main()':
> ft2d.c:13: invalid conversion from `void*' to `double (*)[2]'
> ft2d.c:14: invalid conversion from `void*' to `double (*)[2]'
>

You don't note in your code what lines 13 and 14 are, but if I'm counting
correctly, the errors are on the fftw_malloc lines, right?  You probably
need to cast the results of those function calls to (fftw_complex *).  It
appears that the fftw_malloc call returns a void*, and the compiler is
complaining about that type not matching your in and out variables' declared
type.

-Howard

> Here is my code:
>
> #include <fftw3.h>
> #include <math.h>
>
> int main(void)
> {
>     fftw_complex *in, *out;
>     fftw_plan p;
>     int nx = 5;
>     int ny = 5;
>     int i;
>
>     /* Allocate the input and output arrays, and create the plan */
>     in = fftw_malloc(sizeof(fftw_complex) * nx * ny);
>     out = fftw_malloc(sizeof(fftw_complex) * nx * ny);

"Erica" <erica@technodyke.com> wrote in message 
news:346a55df.0409151004.7edf489e@posting.google.com...
> Hi,
>
> I am currently working on a program using FFTW-> http://www.fftw.org .
> My basic C program to compute the 2D Fourier transform of a bunch of
> data works fine when I compile it with gcc. However, I would like to
> incorporate that code into a larger program that I wrote with C++.
> Unfortunately, I cannot get my program to compile with g++.
>
> I compile it as follows:
>
> g++ ft2d.c -o ft2d -I/usr/local/include -L /usr/local/lib -lfftw3 -lm
>
> The errors I get are:
>
> ft2d.c: In function `int main()':
> ft2d.c:13: invalid conversion from `void*' to `double (*)[2]'
> ft2d.c:14: invalid conversion from `void*' to `double (*)[2]'

This is one of the differences between C++ and C. In C void* automatically 
converts to any other pointer, in C++ you must cast.

>
> Here is my code:
>
> #include <fftw3.h>
> #include <math.h>
>
> int main(void)
> {
>    fftw_complex *in, *out;
>    fftw_plan p;
>    int nx = 5;
>    int ny = 5;
>    int i;
>
>    /* Allocate the input and output arrays, and create the plan */
>    in = fftw_malloc(sizeof(fftw_complex) * nx * ny);

   in = (fftw_complex*)fftw_malloc(sizeof(fftw_complex) * nx * ny);

>    out = fftw_malloc(sizeof(fftw_complex) * nx * ny);

   out = (fftw_complex*)fftw_malloc(sizeof(fftw_complex) * nx * ny);

That should do it.

john

Hi,

I am currently working on a program using FFTW-> http://www.fftw.org .
My basic C program to compute the 2D Fourier transform of a bunch of
data works fine when I compile it with gcc. However, I would like to
incorporate that code into a larger program that I wrote with C++.
Unfortunately, I cannot get my program to compile with g++. 

I compile it as follows:

g++ ft2d.c -o ft2d -I/usr/local/include -L /usr/local/lib -lfftw3 -lm

The errors I get are:

ft2d.c: In function `int main()':
ft2d.c:13: invalid conversion from `void*' to `double (*)[2]'
ft2d.c:14: invalid conversion from `void*' to `double (*)[2]'

Here is my code:

#include <fftw3.h>
#include <math.h>

int main(void)
{
    fftw_complex *in, *out;
    fftw_plan p;
    int nx = 5;
    int ny = 5;
    int i;

    /* Allocate the input and output arrays, and create the plan */
    in = fftw_malloc(sizeof(fftw_complex) * nx * ny);
    out = fftw_malloc(sizeof(fftw_complex) * nx * ny);
    p = fftw_plan_dft_2d(nx, ny, in, out, FFTW_FORWARD,
FFTW_ESTIMATE);

    /* Now fill the input array with the input data */
    /* We'll simply make a sine wave */
    for (i = 0; i < (nx * ny); i++) {
        in[i][0] = sin(i / 10.0 * M_PI);    /* Real part */
        in[i][1] = 0.0;                          /* Imaginary part */
    }

    /* Actually execute the plan on the input data */
    fftw_execute(p);

    /* Print out the results */
    for (i = 0; i < (nx * ny); i++)
        printf("Coefficient %d: %f%+f*i\n", i, out[i][0], out[i][1]);

    /* Clean up after ourselves */
    fftw_destroy_plan(p);
    fftw_free(in); fftw_free(out);
    return 0;
} 

Eventually I will do something more complex than a sine wave, but you
get the idea.

If anyone knows what the problem is, I would greatly appreciate any
help. This is all that fftw.org has about calling it from C++:
http://fftw.org/faq/section2.html#cplusplus

Thanks in advance!!
--Erica