netcdf-c/ncdap_test/test_nstride_cached.c

/*
Report from Ansely Manke:
I've attached a file with a short c program that
demonstrates what I'm seeing. I don't know that we'd call
this a constraint, so that was a misleading description.

The thing I'm mimicking is a sequence where I read the 2-D
coordinate variables, make some decisions about the size of
a subset region, and then define index ranges and strides
for reading other variables.  Reading the full variable
happens correctly, but the read with strides winds up
messing up the data.  Here it shows up returning some valid
data and some zero's, but in other sequences of events it
seems to be actually mis-ordered.

I notice that the results are correct if the initial read of
the variable uses counts that are size-1. So that might be a
clue.  And the read is correct if I either close and reopen
the dataset after reading the original full variable, or if
I don't do that step of first reading the whole grid. It's
also fine with NetCDF 4.2.1.1.

-Ansley

Problem was two-fold:
1. struct Getvara has the dsttype field as OC_Type rather than nc_type
2. the dap odometer code dapnew_segment was incorrectly
   handling strides > 1: specifically, the stop position was incorrect.

*/

/* vars_whoi_test */
/* acm 4/2013 */
/* ansley.b.manke@noaa.gov */

/* test nc_get_vars_float with calls similar to Ferret calls */


/*linked with:

cc vars_whoi_test.c -g -o vars_whoi_test_4211 /usr/local/netcdf_4211/lib/libnetcdf.a /usr/local/hdf5_189/lib/libhdf5_hl.a /usr/local/hdf5_189/lib/libhdf5.a /usr/local/lib/libz.a -L/usr/lib64 -lc -lm -lcurl
cc vars_whoi_test.c -g -o vars_whoi_test /home/users/ansley/local/x86_nc43/lib/libnetcdf.a /usr/local/hdf5_189/lib/libhdf5_hl.a /usr/local/hdf5_189/lib/libhdf5.a /usr/local/lib/libz.a -L/usr/lib64 -lc -lm -lcurl

Closing and reopening the dataset between the two reads fixes the
incorrect data return

Setting the count to one less in the full data read also fixes the
incorrect data return
*/

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include "netcdf.h"

#define VERBOSE 1

/*
2014-07-01: (DMH) Changed the URL to use one from remotetest server.
to remove dependence on an external server.
*/

/*
static char* URL="http://geoport.whoi.edu/thredds/dodsC/coawst_4/use/fmrc/coawst_4_use_best.ncd";
Float64 lon_rho[eta_rho = 336][xi_rho = 896];
Float64 lat_rho[eta_rho = 336][xi_rho = 896];
*/

static char* URL="https://remotetest.unidata.ucar.edu/thredds/dodsC/testdods/rtofs.nc";
#define VAR1 "Latitude"
#define VAR2 "Longitude"
#define XSIZE 850
#define YSIZE 712

int
main()
{

    int ncid;
    int varid;
    int i;
    int ncstatus;
    size_t start[5], count[5];
    ptrdiff_t stride[5], tmp_ptrdiff_t;
    int pass = 1;
    int nelems = XSIZE*YSIZE;

    int idim, ndim;
    float *dat = (float*)malloc(sizeof(float)*nelems);
    float sdat[10];

    for (idim=0; idim<5; idim++) {
        start[idim] = 0;
        count[idim] = 1;
        stride[idim] = 1;
    }

    ndim=2;

    printf(" \n");
    printf("********************\n");
    printf("open URL %s\n",URL);
    printf(" \n");

    ncstatus = nc_open(URL, NC_NOWRITE, &ncid);

    if(ncstatus != NC_NOERR) {
	fprintf(stderr,"Could not open: %s; server may be down; test ignored\n",URL);
	exit(0);
    }

    ncstatus = nc_inq_varid(ncid, VAR1, &varid);

    ndim=2;


#ifdef VERBOSE
    printf(" \n");
    printf("********************\n");
    printf("Read %s data w/o strides\n",VAR1);
    printf(" \n");
#endif

    start[0] = 0;
    start[1] = 0;
    start[2] = 0;
    start[3] = 0;

    count[0] =  XSIZE;
    count[1] =  YSIZE;

    stride[0] = 1;
    stride[1] = 1;

#ifdef VERBOSE
    for (idim=0; idim<ndim; idim++)
	printf("start[%1d]=%3lu count[%1d]=%3lu stride[%1d]=%3lu\n",
		idim,start[idim],idim,count[idim],idim,stride[idim]);
#endif

    ncstatus = nc_get_vars_float (ncid, varid, start, count, stride, (float*) dat);

#ifdef VERBOSE
    printf(" \n");
    printf("********************\n");
    printf("Print some of %s\n",VAR1);
    printf(" \n");

    for (i=0; i<10; i++)
        printf("%s[%d] = %f\n",VAR1,i,dat[i]);
    printf(" \n");


    for (i=(nelems-11); i<(nelems-1); i++)
        printf("%s[%d] = %f\n",VAR1,i,dat[i]);
    printf(" \n");
#endif

    memset((void*)dat,0,sizeof(dat));

    /* Read a second variable */

    ncstatus = nc_inq_varid(ncid, VAR2, &varid);

    ndim=2;

#ifdef VERBOSE
    printf(" \n");
    printf("********************\n");
    printf("Read %s data w/o strides\n",VAR2);
    printf(" \n");
#endif

    start[0] = 0;
    start[1] = 0;
    start[2] = 0;
    start[3] = 0;

    count[0] =  XSIZE;
    count[1] =  YSIZE;

    stride[0] = 1;
    stride[1] = 1;

#ifdef VERBOSE
    for (idim=0; idim<ndim; idim++)
        printf("start[%d]=%3lu count[%d]=%3lu stride[%d]=%3lu\n",
		idim, start[idim], idim, count[idim], idim, stride[idim]);
#endif

    ncstatus = nc_get_vars_float (ncid, varid, start, count, stride, (float*) dat);

#ifdef VERBOSE
    printf(" \n");
    printf("********************\n");
    printf("Print some of %s\n",VAR2);
    printf(" \n");
    for (i=0; i<10; i++)
        printf("%s[%d] = %f\n",VAR2,i,dat[i]);
    printf(" \n");

    printf(" \n");
    for (i=(nelems-11); i<(nelems-1); i++)
        printf("%s[%d] = %f\n",VAR2,i,dat[i]);
    printf(" \n");
#endif

    memset((void*)dat,0,sizeof(dat));

    /* close and reopen the dataset, then the below read is correct */

#ifdef VERBOSE
    printf(" \n");
    printf("********************\n");
    printf("Close and reopen the dataset\n");
#endif

    ncstatus = nc_close (ncid);
    ncstatus = nc_open(URL, NC_NOWRITE, &ncid);

    /*  ----------------------------------------------------- */
    /* Read a subset of the data with strides */

    ncstatus = nc_inq_varid(ncid, VAR1, &varid);

#ifdef VERBOSE
    printf(" \n");
    printf("********************\n");
    printf("Read a subset of %s data with strides\n",VAR1);
    printf(" \n");
#endif

    start[0] = 250;
    start[1] = 704;

    count[0] =  5;
    count[1] =  2;

    stride[0] = 2;
    stride[1] = 4;

#ifdef VERBOSE
    for (idim=0; idim<ndim; idim++)
	printf("start[%1d]=%3lu count[%1d]=%3lu stride[%1d]=%3lu\n",
		idim,start[idim],idim,count[idim],idim,stride[idim]);
#endif

    memset((void*)sdat,0,sizeof(sdat));
    ncstatus = nc_get_vars_float (ncid, varid, start, count, stride,  (float*) sdat);

    printf("status = %d\n", ncstatus);

    /* Verify that all read values are 50 <= n < 51 */
    for (i=0; i<10; i++) {
	if(sdat[i] <= 50.0 || sdat[i] > 51.0) {
	    printf("Out of range: %s[%d] = %f\n",VAR1, i,sdat[i]);
	    pass = 0;
	}
    }

#ifdef VERBOSE
    printf(" \n");
    printf("********************\n");
    printf("Print  values read. They should all be 50.xxxx \n");
    printf(" \n");

    for (i=0; i<10; i++)
        printf("%s[%d] = %f\n",VAR1,i,sdat[i]);
#endif

    ncstatus = nc_close (ncid);

    if(!pass) {
	printf("*** FAIL: %s value out of range.\n",VAR1);
	exit(1);
    }

    printf("*** PASS\n");
    free(dat);
    exit(0);

}