Use of stack allocated vectors with the GNU Scientific Library.

test_stack_allocation_of_vectors.c

/*
  Compile with:
  gcc -Wall -std=c99 test_stack_allocation_of_vectors.c -o test_stack_allocation_of_vectors `gsl-config --libs`
*/

#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <assert.h>

#include <gsl/gsl_vector.h>
#include <gsl/gsl_blas.h>


#define block_init(size_, data_) { .size = size_, .data = data_ }
        
#define vector_from_block_init(block, offset, n, stride_)      \
        { .data = block.data + offset,                         \
          .size = n, .stride = stride_, .owner = 0 }


static void test_stack_allocation_of_vectors(const size_t N)
{
        assert(N >= 4);

        double buf[N];
        gsl_block b = block_init(N, buf);
        gsl_vector u = vector_from_block_init(b, 0, 2, 1);
	gsl_vector v = vector_from_block_init(b, 2, 2, 1);

        gsl_vector_set_basis(&u, 0);
        gsl_vector_set_basis(&v, 1);

        gsl_vector_fprintf(stdout, &u, "%g");
        gsl_vector_fprintf(stdout, &v, "%g");

        double res[3];
        gsl_blas_ddot(&u, &u, &res[0]);
        gsl_blas_ddot(&u, &v, &res[1]);
        gsl_blas_ddot(&v, &v, &res[2]);
        printf("<u, u> = %g, <u, v> = %g, <v, v> = %g\n", res[0], res[1], res[2]);
}


int main(int argc, char *argv[])
{
        if (argc < 2) {
                fprintf(stderr, "Usage: %s NUMBER\n", argv[0]);
                exit(EXIT_FAILURE);
        }

        test_stack_allocation_of_vectors((size_t) atoi(argv[1]));
        
        exit(EXIT_SUCCESS);
}