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<div class="title">NetCDF Example Programs </div> </div>
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<div class="toc"><h3>Table of Contents</h3>
<ul><li class="level1"><a href="#example_simple_xy">The simple_xy Example</a></li>
<li class="level1"><a href="#example_sfc_pres_temp">The sfc_pres_temp Example</a></li>
<li class="level1"><a href="#example_pres_temp_4D">The pres_temp_4D Example</a></li>
<li class="level1"><a href="#example_simple_nc4">The simple_nc4 Example</a></li>
<li class="level1"><a href="#example_simple_xy_nc4">The simple_xy_nc4 Example</a></li>
</ul>
</div>
<div class="textblock"><p>The netCDF example programs show how to use netCDF.</p>
<p>In the netCDF distribution, the “examples” directory contains examples in C and CDL. The examples create, and then read, example data files of increasing complexity.</p>
<p>There are three sets of netCDF classic example programs; corresponding examples are included with the netCDF Fortran and C++ APIs.</p><ul>
<li><a class="el" href="examples1.html#example_simple_xy">The simple_xy Example</a></li>
<li><a class="el" href="examples1.html#example_sfc_pres_temp">The sfc_pres_temp Example</a></li>
<li><a class="el" href="examples1.html#example_pres_temp_4D">The pres_temp_4D Example</a></li>
</ul>
<p>Any existing netCDF applications can be converted to generate netCDF-4/HDF5 files. Simply change the file creation call to include the correct mode flag.</p>
<p>In one of the netCDF classic examples which write a data file, change the <a class="el" href="group__datasets.html#ga427f5a0b24f1d426a99bcc37b8a39cac" title="Create a new netCDF file. ">nc_create()</a> call so that <a class="el" href="netcdf_8h.html#a0d505827d0bdef8a011faf73c5331b9b" title="Use netCDF-4/HDF5 format. ">NC_NETCDF4</a> is one of the flags set on the create.</p>
<p>The corresponding read example will work without modification; netCDF will notice that the file is a NetCDF-4/HDF5 file, and will read it automatically, just as if it were a netCDF classic format file.</p>
<p>In the example in this section we show some of the advanced features of netCDF-4.</p><ul>
<li><a class="el" href="examples1.html#example_simple_nc4">The simple_nc4 Example</a></li>
<li><a class="el" href="examples1.html#example_simple_xy_nc4">The simple_xy_nc4 Example</a></li>
</ul>
<p>The examples are built and run with the “make check” command. (See <a class="el" href="getting_and_building_netcdf.html#building">Building netCDF-C </a>).</p>
<p>The corresponding examples in each language create identical netCDF data files. For example, the C program <a class="el" href="sfc__pres__temp__wr_8c.html" title="A simple example of writing a netCDF file. ">sfc_pres_temp_wr.c</a> produces the same data file as the Fortran 77 program sfc_pres_temp_wr.f.</p>
<h1><a class="anchor" id="example_simple_xy"></a>
The simple_xy Example</h1>
<p>This example is an unrealistically simple netCDF file, to demonstrate the minimum operation of the netCDF APIs. Users should seek to make their netCDF files more self-describing than this primitive example.</p><ul>
<li><a class="el" href="simple__xy__wr_8c.html" title="An example program demonstrating a simple 2D write. ">simple_xy_wr.c</a></li>
<li><a class="el" href="simple__xy__rd_8c.html" title="Write a file demonstrating some of the features of netCDF-4. ">simple_xy_rd.c</a></li>
</ul>
<p>As in all the netCDF tutorial examples, this example file can be created by C and by ncgen, which creates it from a CDL script. Both ncgen and the C example create identical files, “simple_xy.nc.”</p>
<p>The simple_xy.nc data file contains two dimensions, “x” and “y”, and one netCDF variable, “data.”</p>
<p>The CDL for this example is shown below. For more information on ncdump and ncgen see NetCDF Utilities.</p>
<div class="fragment"><div class="line">netcdf simple_xy {</div><div class="line">dimensions:</div><div class="line"> x = 6 ;</div><div class="line"> y = 12 ;</div><div class="line">variables:</div><div class="line"> <span class="keywordtype">int</span> data(x, y) ;</div><div class="line">data:</div><div class="line"></div><div class="line"> data =</div><div class="line"> 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,</div><div class="line"> 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,</div><div class="line"> 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,</div><div class="line"> 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,</div><div class="line"> 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59,</div><div class="line"> 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71 ;</div><div class="line">}</div></div><!-- fragment --><h1><a class="anchor" id="example_sfc_pres_temp"></a>
The sfc_pres_temp Example</h1>
<p>This example has been constructed for the meteorological mind.</p>
<p>Suppose you have some data you want to write to a netCDF file. For example, you have one time step of surface temperature and surface pressure, on a 6 x 12 latitude longitude grid.</p>
<p>To store this in netCDF, create a file, add two dimensions (latitude and longitude) and two variables (pressure and temperature).</p><ul>
<li><a class="el" href="sfc__pres__temp__wr_8c.html" title="A simple example of writing a netCDF file. ">sfc_pres_temp_wr.c</a></li>
<li><a class="el" href="sfc__pres__temp__rd_8c.html" title="A simple example of reading a netCDF file. ">sfc_pres_temp_rd.c</a></li>
</ul>
<p>In this example we add some netCDF attributes, as is typical in scientific applications, to further describe the data. In this case we add a units attribute to every netCDF variable.</p>
<p>In this example we also add additional netCDF variables to describe the coordinate system. These “coordinate variables” allow us to specify the latitudes and longitudes that describe the data grid.</p>
<p>The CDL version of the data file, generated by ncdump, is shown below (see <a class="el" href="netcdf_working_with_netcdf_files.html#netcdf_utilities">The NetCDF Utilities</a>).</p>
<div class="fragment"><div class="line">netcdf sfc_pres_temp {</div><div class="line">dimensions:</div><div class="line"> latitude = 6 ;</div><div class="line"> longitude = 12 ;</div><div class="line">variables:</div><div class="line"> <span class="keywordtype">float</span> latitude(latitude) ;</div><div class="line"> latitude:units = <span class="stringliteral">"degrees_north"</span> ;</div><div class="line"> <span class="keywordtype">float</span> longitude(longitude) ;</div><div class="line"> longitude:units = <span class="stringliteral">"degrees_east"</span> ;</div><div class="line"> <span class="keywordtype">float</span> pressure(latitude, longitude) ;</div><div class="line"> pressure:units = <span class="stringliteral">"hPa"</span> ;</div><div class="line"> <span class="keywordtype">float</span> temperature(latitude, longitude) ;</div><div class="line"> temperature:units = <span class="stringliteral">"celsius"</span> ;</div><div class="line">data:</div><div class="line"></div><div class="line"> latitude = 25, 30, 35, 40, 45, 50 ;</div><div class="line"></div><div class="line"> longitude = -125, -120, -115, -110, -105, -100, -95, -90, -85, -80, -75, -70 ;</div><div class="line"></div><div class="line"> pressure =</div><div class="line"> 900, 906, 912, 918, 924, 930, 936, 942, 948, 954, 960, 966,</div><div class="line"> 901, 907, 913, 919, 925, 931, 937, 943, 949, 955, 961, 967,</div><div class="line"> 902, 908, 914, 920, 926, 932, 938, 944, 950, 956, 962, 968,</div><div class="line"> 903, 909, 915, 921, 927, 933, 939, 945, 951, 957, 963, 969,</div><div class="line"> 904, 910, 916, 922, 928, 934, 940, 946, 952, 958, 964, 970,</div><div class="line"> 905, 911, 917, 923, 929, 935, 941, 947, 953, 959, 965, 971 ;</div><div class="line"></div><div class="line"> temperature =</div><div class="line"> 9, 10.5, 12, 13.5, 15, 16.5, 18, 19.5, 21, 22.5, 24, 25.5,</div><div class="line"> 9.25, 10.75, 12.25, 13.75, 15.25, 16.75, 18.25, 19.75, 21.25, 22.75, 24.25,</div><div class="line"> 25.75,</div><div class="line"> 9.5, 11, 12.5, 14, 15.5, 17, 18.5, 20, 21.5, 23, 24.5, 26,</div><div class="line"> 9.75, 11.25, 12.75, 14.25, 15.75, 17.25, 18.75, 20.25, 21.75, 23.25, 24.75,</div><div class="line"> 26.25,</div><div class="line"> 10, 11.5, 13, 14.5, 16, 17.5, 19, 20.5, 22, 23.5, 25, 26.5,</div><div class="line"> 10.25, 11.75, 13.25, 14.75, 16.25, 17.75, 19.25, 20.75, 22.25, 23.75,</div><div class="line"> 25.25, 26.75 ;</div><div class="line">}</div></div><!-- fragment --><h1><a class="anchor" id="example_pres_temp_4D"></a>
The pres_temp_4D Example</h1>
<p>This example expands on the previous example by making our two-dimensional data into four-dimensional data, adding a vertical level axis and an unlimited time step axis.</p><ul>
<li><a class="el" href="pres__temp__4D__wr_8c.html" title="A more complex example of writing a netCDF file. ">pres_temp_4D_wr.c</a></li>
<li><a class="el" href="pres__temp__4D__rd_8c.html" title="Example program for reading a 4D netCDF file. ">pres_temp_4D_rd.c</a></li>
</ul>
<p>Additionally, in this example the data are written and read one time step at a time, as is typical in scientific applications that use the unlimited dimension.</p>
<p>The sample data file created by pres_temp_4D_wr can be examined with the utility ncdump (see <a class="el" href="netcdf_working_with_netcdf_files.html#netcdf_utilities">The NetCDF Utilities</a>).</p>
<div class="fragment"><div class="line">netcdf pres_temp_4D {</div><div class="line">dimensions:</div><div class="line"> level = 2 ;</div><div class="line"> latitude = 6 ;</div><div class="line"> longitude = 12 ;</div><div class="line"> time = UNLIMITED ; <span class="comment">// (2 currently)</span></div><div class="line">variables:</div><div class="line"> <span class="keywordtype">float</span> latitude(latitude) ;</div><div class="line"> latitude:units = <span class="stringliteral">"degrees_north"</span> ;</div><div class="line"> <span class="keywordtype">float</span> longitude(longitude) ;</div><div class="line"> longitude:units = <span class="stringliteral">"degrees_east"</span> ;</div><div class="line"> <span class="keywordtype">float</span> pressure(time, level, latitude, longitude) ;</div><div class="line"> pressure:units = <span class="stringliteral">"hPa"</span> ;</div><div class="line"> <span class="keywordtype">float</span> temperature(time, level, latitude, longitude) ;</div><div class="line"> temperature:units = <span class="stringliteral">"celsius"</span> ;</div><div class="line">data:</div><div class="line"></div><div class="line"> latitude = 25, 30, 35, 40, 45, 50 ;</div><div class="line"></div><div class="line"> longitude = -125, -120, -115, -110, -105, -100, -95, -90, -85, -80, -75, -70 ;</div><div class="line"></div><div class="line"> pressure =</div><div class="line"> 900, 901, 902, 903, 904, 905, 906, 907, 908, 909, 910, 911,</div><div class="line"> 912, 913, 914, 915, 916, 917, 918, 919, 920, 921, 922, 923,</div><div class="line"> 924, 925, 926, 927, 928, 929, 930, 931, 932, 933, 934, 935,</div><div class="line"> 936, 937, 938, 939, 940, 941, 942, 943, 944, 945, 946, 947,</div><div class="line"> 948, 949, 950, 951, 952, 953, 954, 955, 956, 957, 958, 959,</div><div class="line"> 960, 961, 962, 963, 964, 965, 966, 967, 968, 969, 970, 971,</div><div class="line"> 972, 973, 974, 975, 976, 977, 978, 979, 980, 981, 982, 983,</div><div class="line"> 984, 985, 986, 987, 988, 989, 990, 991, 992, 993, 994, 995,</div><div class="line"> 996, 997, 998, 999, 1000, 1001, 1002, 1003, 1004, 1005, 1006, 1007,</div><div class="line"> 1008, 1009, 1010, 1011, 1012, 1013, 1014, 1015, 1016, 1017, 1018, 1019,</div><div class="line"> 1020, 1021, 1022, 1023, 1024, 1025, 1026, 1027, 1028, 1029, 1030, 1031,</div><div class="line"> 1032, 1033, 1034, 1035, 1036, 1037, 1038, 1039, 1040, 1041, 1042, 1043,</div><div class="line"> 900, 901, 902, 903, 904, 905, 906, 907, 908, 909, 910, 911,</div><div class="line"> 912, 913, 914, 915, 916, 917, 918, 919, 920, 921, 922, 923,</div><div class="line"> 924, 925, 926, 927, 928, 929, 930, 931, 932, 933, 934, 935,</div><div class="line"> 936, 937, 938, 939, 940, 941, 942, 943, 944, 945, 946, 947,</div><div class="line"> 948, 949, 950, 951, 952, 953, 954, 955, 956, 957, 958, 959,</div><div class="line"> 960, 961, 962, 963, 964, 965, 966, 967, 968, 969, 970, 971,</div><div class="line"> 972, 973, 974, 975, 976, 977, 978, 979, 980, 981, 982, 983,</div><div class="line"> 984, 985, 986, 987, 988, 989, 990, 991, 992, 993, 994, 995,</div><div class="line"> 996, 997, 998, 999, 1000, 1001, 1002, 1003, 1004, 1005, 1006, 1007,</div><div class="line"> 1008, 1009, 1010, 1011, 1012, 1013, 1014, 1015, 1016, 1017, 1018, 1019,</div><div class="line"> 1020, 1021, 1022, 1023, 1024, 1025, 1026, 1027, 1028, 1029, 1030, 1031,</div><div class="line"> 1032, 1033, 1034, 1035, 1036, 1037, 1038, 1039, 1040, 1041, 1042, 1043 ;</div><div class="line"></div><div class="line"> temperature =</div><div class="line"> 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,</div><div class="line"> 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32,</div><div class="line"> 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44,</div><div class="line"> 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56,</div><div class="line"> 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,</div><div class="line"> 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80,</div><div class="line"> 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92,</div><div class="line"> 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104,</div><div class="line"> 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116,</div><div class="line"> 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128,</div><div class="line"> 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140,</div><div class="line"> 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152,</div><div class="line"> 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,</div><div class="line"> 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32,</div><div class="line"> 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44,</div><div class="line"> 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56,</div><div class="line"> 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,</div><div class="line"> 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80,</div><div class="line"> 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92,</div><div class="line"> 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104,</div><div class="line"> 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116,</div><div class="line"> 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128,</div><div class="line"> 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140,</div><div class="line"> 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152 ;</div><div class="line">}</div></div><!-- fragment --><h1><a class="anchor" id="example_simple_nc4"></a>
The simple_nc4 Example</h1>
<p>This example, like the simple_xy netCDF-3 example above, is an overly simplified example which demonstrates how to use groups in a netCDF-4 file.</p>
<p>This example is only available in C for this version of netCDF-4. The example creates and then reads the file “simple_nc4.nc.”</p>
<p>The simple_xy.nc data file contains two dimensions, “x” and “y”, two groups, “grp1” and “grp2”, and two data variables, one in each group, both named: “data.” One data variable is an unsigned 64-bit integer, the other a user-defined compound type.</p>
<p>The example program <a class="el" href="simple__nc4__wr_8c.html" title="Write a file demonstrating some of the features of netCDF-4. ">simple_nc4_wr.c</a> creates the example data file simple_nc4.nc. The example program <a class="el" href="simple__nc4__rd_8c.html" title="Read a simple file, with some of the features of netCDF-4. ">simple_nc4_rd.c</a> reads the data file.</p><ul>
<li><a class="el" href="simple__nc4__wr_8c.html" title="Write a file demonstrating some of the features of netCDF-4. ">simple_nc4_wr.c</a></li>
<li><a class="el" href="simple__nc4__rd_8c.html" title="Read a simple file, with some of the features of netCDF-4. ">simple_nc4_rd.c</a></li>
</ul>
<h1><a class="anchor" id="example_simple_xy_nc4"></a>
The simple_xy_nc4 Example</h1>
<p>This example, like the simple_xy netCDF-3 example above, is an overly simplified example. It is based on the simple_xy example, but used data chunking, compression, and the fletcher32 filter.</p>
<p>(These are all HDF5 features. For more information see <a href="http://hdfgroup.org/HDF5/">http://hdfgroup.org/HDF5/</a>).</p>
<p>This example is not yet available in C++. We hope to have the C++ example in a future release of netCDF.</p>
<p>The example creates and then reads the file “simple_xy_nc4.nc.”</p>
<p>The example program <a class="el" href="simple__xy__nc4__wr_8c.html" title="Write the simple_xy file, with some of the features of netCDF-4. ">simple_xy_nc4_wr.c</a> creates the example data file simple_xy_nc4.nc. The example program <a class="el" href="simple__xy__nc4__rd_8c.html" title="Read the simple_xy file, with some of the features of netCDF-4. ">simple_xy_nc4_rd.c</a> reads the data file.</p><ul>
<li><a class="el" href="simple__xy__nc4__wr_8c.html" title="Write the simple_xy file, with some of the features of netCDF-4. ">simple_xy_nc4_wr.c</a></li>
<li><a class="el" href="simple__xy__nc4__rd_8c.html" title="Read the simple_xy file, with some of the features of netCDF-4. ">simple_xy_nc4_rd.c</a> </li>
</ul>
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