Failure to use PetscFListGet for listing available KSP types

crashpetscflistget.c

#include <petscsys.h>
#include <petscksp.h>

// Struct copied from reg.c so we can access the members of a PetscFList
struct _n_PetscFList {
  void        (*routine)(void);   /* the routine */
  char        *path;              /* path of link library containing routine */
  char        *name;              /* string to identify routine */
  char        *rname;             /* routine name in dynamic library */
  PetscFList  next;               /* next pointer */
  PetscFList  next_list;          /* used to maintain list of all lists for freeing */
};

int main(int argc,char **argv)
{
  PetscErrorCode ierr;
  KSP ksp;

  ierr = PetscInitialize(&argc,&argv,PETSC_NULL,PETSC_NULL);CHKERRQ(ierr);
  // Create a KSP context so that KSPList is initialised
  KSPCreate(PETSC_COMM_WORLD,&ksp);

  PetscFList list = KSPList;
  int count = 0;

  // Manually iterate over the KSPList (inspired by the code in PetscFListGet)
  // Works OK
  while (list) {
    printf("%d: %s\n", count, list->name);
    list = list->next;
    count++;
  }

  // Get the array of names with PetscFlistGet. Segfaults in PetscTrMalloc...
  char ***array;
  int *n;
  ierr = PetscFListGet(KSPList, array, n);

  // Print the array (should be the same as before)
  for (int i=0; i<*n; ++i)
    printf("%s\n", *array[i]);

  ierr = PetscFinalize();
  return ierr;
}

You want:

#include <petscsys.h>
#include <petscksp.h>

int main(int argc,char **argv)
{
  PetscErrorCode ierr;
  KSP ksp;

  ierr = PetscInitialize(&argc,&argv,PETSC_NULL,PETSC_NULL);CHKERRQ(ierr);
  // Create a KSP context so that KSPList is initialised
  KSPCreate(PETSC_COMM_WORLD,&ksp);
  KSPDestroy(ksp);
  PetscFList list = KSPList;

  char **array;
  int n;
  ierr = PetscFListGet(KSPList, &array, &n);

  /* Last entry in array is NULL (this is non-obvious) */
  int i;
  for ( i = 0; *array; i++ ) {
      printf("%d: %s\n", i, *(array++));
  }

  array -= i;
  PetscFree(array);
  ierr = PetscFinalize();
  return ierr;
}