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/* This is part of the netCDF package.
Copyright 2006 University Corporation for Atmospheric Research/Unidata.
See COPYRIGHT file for conditions of use.
This is an example which reads some surface pressure and
temperatures. The data file read by this program is produced
companion program sfc_pres_temp_wr.cxx. It is intended to
illustrate the use of the netCDF C++ API.
This program is part of the netCDF tutorial:
http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-tutorial
Full documentation of the netCDF C++ API can be found at:
http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-cxx
$Id: sfc_pres_temp_rd.cpp,v 1.17 2008/05/16 13:42:28 ed Exp $
*/
#include <iostream>
#include <cstring>
#include <netcdfcpp.h>
using namespace std;
// We are reading 2D data, a 6 x 12 lat-lon grid.
static const int NLAT = 6;
static const int NLON = 12;
// These are used to calculate the values we expect to find.
static const float SAMPLE_PRESSURE = 900;
static const float SAMPLE_TEMP = 9.0;
static const float START_LAT = 25.0;
static const float START_LON = -125.0;
// Return this code to the OS in case of failure.
static const int NC_ERR = 2;
int main(void)
{
// These will hold our pressure and temperature data.
float presIn[NLAT][NLON];
float tempIn[NLAT][NLON];
// These will hold our latitudes and longitudes.
float latsIn[NLAT];
float lonsIn[NLON];
// Change the error behavior of the netCDF C++ API by creating an
// NcError object. Until it is destroyed, this NcError object will
// ensure that the netCDF C++ API silently returns error codes on
// any failure, and leaves any other error handling to the calling
// program. In the case of this example, we just exit with an
// NC_ERR error code.
NcError err(NcError::silent_nonfatal);
// Open the file and check to make sure it's valid.
NcFile dataFile("sfc_pres_temp.nc", NcFile::ReadOnly);
if(!dataFile.is_valid())
return NC_ERR;
// There are a number of inquiry functions in netCDF which can be
// used to learn about an unknown netCDF file. In this case we know
// that there are 2 netCDF dimensions, 4 netCDF variables, no
// global attributes, and no unlimited dimension.
if (dataFile.num_dims() != 2 || dataFile.num_vars() != 4 ||
dataFile.num_atts() != 0 || dataFile.rec_dim() != 0)
return NC_ERR;
// We get back a pointer to each NcVar we request. Get the
// latitude and longitude coordinate variables.
NcVar *latVar, *lonVar;
if (!(latVar = dataFile.get_var("latitude")))
return NC_ERR;
if (!(lonVar = dataFile.get_var("longitude")))
return NC_ERR;
// Read the latitude and longitude coordinate variables into arrays
// latsIn and lonsIn.
if (!latVar->get(latsIn, NLAT))
return NC_ERR;
if (!lonVar->get(lonsIn, NLON))
return NC_ERR;
// Check the coordinate variable data.
for(int lat = 0; lat < NLAT; lat++)
if (latsIn[lat] != START_LAT + 5. * lat)
return NC_ERR;
// Check longitude values.
for (int lon = 0; lon < NLON; lon++)
if (lonsIn[lon] != START_LON + 5. * lon)
return NC_ERR;
// We get back a pointer to each NcVar we request.
NcVar *presVar, *tempVar;
if (!(presVar = dataFile.get_var("pressure")))
return NC_ERR;
if (!(tempVar = dataFile.get_var("temperature")))
return NC_ERR;
// Read the data. Since we know the contents of the file we know
// that the data arrays in this program are the correct size to
// hold all the data.
if (!presVar->get(&presIn[0][0], NLAT, NLON))
return NC_ERR;
if (!tempVar->get(&tempIn[0][0], NLAT, NLON))
return NC_ERR;
// Check the data.
for (int lat = 0; lat < NLAT; lat++)
for (int lon = 0; lon < NLON; lon++)
if (presIn[lat][lon] != SAMPLE_PRESSURE + (lon * NLAT + lat)
|| tempIn[lat][lon] != SAMPLE_TEMP + .25 * (lon * NLAT + lat))
return NC_ERR;
// Each of the netCDF variables has a "units" attribute. Let's read
// them and check them.
NcAtt *att;
char *units;
if (!(att = latVar->get_att("units")))
return NC_ERR;
units = att->as_string(0);
if (strncmp(units, "degrees_north", strlen("degrees_north")))
return NC_ERR;
// Attributes and attribute values should be deleted by the caller
// when no longer needed, to prevent memory leaks.
delete units;
delete att;
if (!(att = lonVar->get_att("units")))
return NC_ERR;
units = att->as_string(0);
if (strncmp(units, "degrees_east", strlen("degrees_east")))
return NC_ERR;
delete units;
delete att;
if (!(att = presVar->get_att("units")))
return NC_ERR;
units = att->as_string(0);
if (strncmp(units, "hPa", strlen("hPa")))
return NC_ERR;
delete units;
delete att;
if (!(att = tempVar->get_att("units")))
return NC_ERR;
units = att->as_string(0);
if (strncmp(units, "celsius", strlen("celsius")))
return NC_ERR;
delete units;
delete att;
// The file will be automatically closed by the destructor. This
// frees up any internal netCDF resources associated with the file,
// and flushes any buffers.
cout << "*** SUCCESS reading example file sfc_pres_temp.nc!" << endl;
return 0;
}
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