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<div class="textblock"><h1><a class="anchor" id="secAttributes"></a>
Attributes</h1>
<h2><a class="anchor" id="CB_LargeAttributes"></a>
Creating "Large" HDF5 Attributes</h2>
<dl class="section user"><dt>Problem</dt><dd>You would like to use HDF5 attributes the size of whose values exceeds a few dozen kilobytes</dd></dl>
<dl class="section user"><dt>Solution</dt><dd>A file format change in the HDF5 1.8.x family of library releases made it possible to have attributes larger than about 64 KiB. Ensure that the lower library version bound for new HDF5 item creation is at least 1.8.x, and create larger attributes as usual.<br />
In the example below, we create an attribute whose value occupies 4 MiB.</dd></dl>
<dl class="section note"><dt>Note</dt><dd>This feature is only supported in HDF5 1.8.x+</dd></dl>
<div class="fragment"><div class="line"><a name="l00015"></a><span class="lineno"> 15</span>  {</div>
<div class="line"><a name="l00016"></a><span class="lineno"> 16</span>  __label__ fail_attr, fail_aspace, fail_fapl, fail_file;</div>
<div class="line"><a name="l00017"></a><span class="lineno"> 17</span>  <a class="code" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> fapl, file, aspace, attr;</div>
<div class="line"><a name="l00018"></a><span class="lineno"> 18</span>  </div>
<div class="line"><a name="l00019"></a><span class="lineno"> 19</span>  <span class="keywordflow">if</span> ((fapl = <a class="code" href="group___p_l_c_r.html#gaf1b11da01d4d45d788c45f8bc5f0cbfa">H5Pcreate</a>(<a class="code" href="_h5_ppublic_8h.html#a60ec2d4334addfc0eda89614598ee38e">H5P_FILE_ACCESS</a>)) < 0) {</div>
<div class="line"><a name="l00020"></a><span class="lineno"> 20</span>  ret_val = EXIT_FAILURE;</div>
<div class="line"><a name="l00021"></a><span class="lineno"> 21</span>  <span class="keywordflow">goto</span> fail_fapl;</div>
<div class="line"><a name="l00022"></a><span class="lineno"> 22</span>  }</div>
<div class="line"><a name="l00023"></a><span class="lineno"> 23</span> <span class="preprocessor">#if H5_VERSION_GE(1, 10, 0)</span></div>
<div class="line"><a name="l00024"></a><span class="lineno"> 24</span>  <span class="keywordflow">if</span> (<a class="code" href="group___f_a_p_l.html#gacbe1724e7f70cd17ed687417a1d2a910">H5Pset_libver_bounds</a>(fapl, <a class="code" href="_h5_fpublic_8h.html#a2d963b599894f684571fbd4d5e8a96a2a434ca8def77a117013577c8cec6af0d8">H5F_LIBVER_V18</a>, <a class="code" href="_h5_fpublic_8h.html#a47d050173da48a2b85c730446f0771c0">H5F_LIBVER_LATEST</a>) < 0) {</div>
<div class="line"><a name="l00025"></a><span class="lineno"> 25</span> <span class="preprocessor">#elif H5_VERSION_GE(1, 8, 0)</span></div>
<div class="line"><a name="l00026"></a><span class="lineno"> 26</span>  <span class="keywordflow">if</span> (<a class="code" href="group___f_a_p_l.html#gacbe1724e7f70cd17ed687417a1d2a910">H5Pset_libver_bounds</a>(fapl, <a class="code" href="_h5_fpublic_8h.html#a47d050173da48a2b85c730446f0771c0">H5F_LIBVER_LATEST</a>, <a class="code" href="_h5_fpublic_8h.html#a47d050173da48a2b85c730446f0771c0">H5F_LIBVER_LATEST</a>) < 0) {</div>
<div class="line"><a name="l00027"></a><span class="lineno"> 27</span> <span class="preprocessor">#else</span></div>
<div class="line"><a name="l00028"></a><span class="lineno"> 28</span> <span class="preprocessor">#error Only HDF5 1.8.x and later supported.</span></div>
<div class="line"><a name="l00029"></a><span class="lineno"> 29</span> <span class="preprocessor">#endif</span></div>
<div class="line"><a name="l00030"></a><span class="lineno"> 30</span>  ret_val = EXIT_FAILURE;</div>
<div class="line"><a name="l00031"></a><span class="lineno"> 31</span>  <span class="keywordflow">goto</span> fail_file;</div>
<div class="line"><a name="l00032"></a><span class="lineno"> 32</span>  }</div>
<div class="line"><a name="l00033"></a><span class="lineno"> 33</span>  <span class="keywordflow">if</span> ((file = <a class="code" href="group___h5_f.html#gae64b51ee9ac0781bc4ccc599d98387f4">H5Fcreate</a>(<span class="stringliteral">"large_attribute.h5"</span>, <a class="code" href="_h5_fpublic_8h.html#a5a2d6726f9ad8d2bca8df2b817e5ad6a">H5F_ACC_TRUNC</a>, <a class="code" href="_h5_ppublic_8h.html#afa85e97bfbf9bf1c58e39263846c568f">H5P_DEFAULT</a>, fapl)) < 0) {</div>
<div class="line"><a name="l00034"></a><span class="lineno"> 34</span>  ret_val = EXIT_FAILURE;</div>
<div class="line"><a name="l00035"></a><span class="lineno"> 35</span>  <span class="keywordflow">goto</span> fail_file;</div>
<div class="line"><a name="l00036"></a><span class="lineno"> 36</span>  }</div>
<div class="line"><a name="l00037"></a><span class="lineno"> 37</span>  </div>
<div class="line"><a name="l00038"></a><span class="lineno"> 38</span>  <span class="keywordflow">if</span> ((aspace = <a class="code" href="group___h5_s.html#ga8e35eea5738b4805856eac7d595254ae">H5Screate_simple</a>(1, (<a class="code" href="_h5public_8h.html#a7f81cce70fb546af88da24d9285d3c1c">hsize_t</a>[]){1024 * 1024}, NULL)) < 0) {</div>
<div class="line"><a name="l00039"></a><span class="lineno"> 39</span>  ret_val = EXIT_FAILURE;</div>
<div class="line"><a name="l00040"></a><span class="lineno"> 40</span>  <span class="keywordflow">goto</span> fail_aspace;</div>
<div class="line"><a name="l00041"></a><span class="lineno"> 41</span>  }</div>
<div class="line"><a name="l00042"></a><span class="lineno"> 42</span>  <span class="keywordflow">if</span> ((attr = <a class="code" href="group___h5_a.html#ga4a76e4e5ab6eb0fd2aa7990d38d55f24">H5Acreate</a>(file, <span class="stringliteral">"4MiB"</span>, <a class="code" href="group___p_d_t_i_e_e_e.html#ga994ce9ffdd2c77a9352b102a883503ea">H5T_IEEE_F32LE</a>, aspace, <a class="code" href="_h5_ppublic_8h.html#afa85e97bfbf9bf1c58e39263846c568f">H5P_DEFAULT</a>, <a class="code" href="_h5_ppublic_8h.html#afa85e97bfbf9bf1c58e39263846c568f">H5P_DEFAULT</a>)) < 0) {</div>
<div class="line"><a name="l00043"></a><span class="lineno"> 43</span>  ret_val = EXIT_FAILURE;</div>
<div class="line"><a name="l00044"></a><span class="lineno"> 44</span>  <span class="keywordflow">goto</span> fail_attr;</div>
<div class="line"><a name="l00045"></a><span class="lineno"> 45</span>  }</div>
<div class="line"><a name="l00046"></a><span class="lineno"> 46</span>  </div>
<div class="line"><a name="l00047"></a><span class="lineno"> 47</span>  <a class="code" href="group___h5_a.html#gaef4394b661e2c930879e9868e122bdda">H5Aclose</a>(attr);</div>
<div class="line"><a name="l00048"></a><span class="lineno"> 48</span> fail_attr:</div>
<div class="line"><a name="l00049"></a><span class="lineno"> 49</span>  <a class="code" href="group___h5_s.html#ga2b53128a39c8f104c1c9c2a91590fcc1">H5Sclose</a>(aspace);</div>
<div class="line"><a name="l00050"></a><span class="lineno"> 50</span> fail_aspace:</div>
<div class="line"><a name="l00051"></a><span class="lineno"> 51</span>  <a class="code" href="group___h5_f.html#gac55cd91d80822e4f8c2a7f04ea71b124">H5Fclose</a>(file);</div>
<div class="line"><a name="l00052"></a><span class="lineno"> 52</span> fail_file:</div>
<div class="line"><a name="l00053"></a><span class="lineno"> 53</span>  <a class="code" href="group___p_l_c_r.html#ga5dce61149211d3ef319452aa598887fb">H5Pclose</a>(fapl);</div>
<div class="line"><a name="l00054"></a><span class="lineno"> 54</span> fail_fapl:;</div>
<div class="line"><a name="l00055"></a><span class="lineno"> 55</span>  }</div>
<div class="ttc" id="a_h5_fpublic_8h_html_a2d963b599894f684571fbd4d5e8a96a2a434ca8def77a117013577c8cec6af0d8"><div class="ttname"><a href="_h5_fpublic_8h.html#a2d963b599894f684571fbd4d5e8a96a2a434ca8def77a117013577c8cec6af0d8">H5F_LIBVER_V18</a></div><div class="ttdeci">@ H5F_LIBVER_V18</div><div class="ttdef"><b>Definition:</b> H5Fpublic.h:187</div></div>
<div class="ttc" id="a_h5_fpublic_8h_html_a47d050173da48a2b85c730446f0771c0"><div class="ttname"><a href="_h5_fpublic_8h.html#a47d050173da48a2b85c730446f0771c0">H5F_LIBVER_LATEST</a></div><div class="ttdeci">#define H5F_LIBVER_LATEST</div><div class="ttdef"><b>Definition:</b> H5Fpublic.h:195</div></div>
<div class="ttc" id="a_h5_fpublic_8h_html_a5a2d6726f9ad8d2bca8df2b817e5ad6a"><div class="ttname"><a href="_h5_fpublic_8h.html#a5a2d6726f9ad8d2bca8df2b817e5ad6a">H5F_ACC_TRUNC</a></div><div class="ttdeci">#define H5F_ACC_TRUNC</div><div class="ttdef"><b>Definition:</b> H5Fpublic.h:50</div></div>
<div class="ttc" id="a_h5_ipublic_8h_html_a0045db7ff9c22ad35db6ae91662e1943"><div class="ttname"><a href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a></div><div class="ttdeci">int64_t hid_t</div><div class="ttdef"><b>Definition:</b> H5Ipublic.h:60</div></div>
<div class="ttc" id="a_h5_ppublic_8h_html_a60ec2d4334addfc0eda89614598ee38e"><div class="ttname"><a href="_h5_ppublic_8h.html#a60ec2d4334addfc0eda89614598ee38e">H5P_FILE_ACCESS</a></div><div class="ttdeci">#define H5P_FILE_ACCESS</div><div class="ttdef"><b>Definition:</b> H5Ppublic.h:52</div></div>
<div class="ttc" id="a_h5_ppublic_8h_html_afa85e97bfbf9bf1c58e39263846c568f"><div class="ttname"><a href="_h5_ppublic_8h.html#afa85e97bfbf9bf1c58e39263846c568f">H5P_DEFAULT</a></div><div class="ttdeci">#define H5P_DEFAULT</div><div class="ttdef"><b>Definition:</b> H5Ppublic.h:102</div></div>
<div class="ttc" id="a_h5public_8h_html_a7f81cce70fb546af88da24d9285d3c1c"><div class="ttname"><a href="_h5public_8h.html#a7f81cce70fb546af88da24d9285d3c1c">hsize_t</a></div><div class="ttdeci">uint64_t hsize_t</div><div class="ttdef"><b>Definition:</b> H5public.h:297</div></div>
<div class="ttc" id="agroup___f_a_p_l_html_gacbe1724e7f70cd17ed687417a1d2a910"><div class="ttname"><a href="group___f_a_p_l.html#gacbe1724e7f70cd17ed687417a1d2a910">H5Pset_libver_bounds</a></div><div class="ttdeci">herr_t H5Pset_libver_bounds(hid_t plist_id, H5F_libver_t low, H5F_libver_t high)</div><div class="ttdoc">Controls the range of library release versions used when creating objects in a file.</div></div>
<div class="ttc" id="agroup___h5_a_html_ga4a76e4e5ab6eb0fd2aa7990d38d55f24"><div class="ttname"><a href="group___h5_a.html#ga4a76e4e5ab6eb0fd2aa7990d38d55f24">H5Acreate</a></div><div class="ttdeci">#define H5Acreate</div><div class="ttdef"><b>Definition:</b> H5version.h:868</div></div>
<div class="ttc" id="agroup___h5_a_html_gaef4394b661e2c930879e9868e122bdda"><div class="ttname"><a href="group___h5_a.html#gaef4394b661e2c930879e9868e122bdda">H5Aclose</a></div><div class="ttdeci">herr_t H5Aclose(hid_t attr_id)</div><div class="ttdoc">Closes the specified attribute.</div></div>
<div class="ttc" id="agroup___h5_f_html_gac55cd91d80822e4f8c2a7f04ea71b124"><div class="ttname"><a href="group___h5_f.html#gac55cd91d80822e4f8c2a7f04ea71b124">H5Fclose</a></div><div class="ttdeci">herr_t H5Fclose(hid_t file_id)</div><div class="ttdoc">Terminates access to an HDF5 file.</div></div>
<div class="ttc" id="agroup___h5_f_html_gae64b51ee9ac0781bc4ccc599d98387f4"><div class="ttname"><a href="group___h5_f.html#gae64b51ee9ac0781bc4ccc599d98387f4">H5Fcreate</a></div><div class="ttdeci">hid_t H5Fcreate(const char *filename, unsigned flags, hid_t fcpl_id, hid_t fapl_id)</div><div class="ttdoc">Creates an HDF5 file.</div></div>
<div class="ttc" id="agroup___h5_s_html_ga2b53128a39c8f104c1c9c2a91590fcc1"><div class="ttname"><a href="group___h5_s.html#ga2b53128a39c8f104c1c9c2a91590fcc1">H5Sclose</a></div><div class="ttdeci">herr_t H5Sclose(hid_t space_id)</div><div class="ttdoc">Releases and terminates access to a dataspace.</div></div>
<div class="ttc" id="agroup___h5_s_html_ga8e35eea5738b4805856eac7d595254ae"><div class="ttname"><a href="group___h5_s.html#ga8e35eea5738b4805856eac7d595254ae">H5Screate_simple</a></div><div class="ttdeci">hid_t H5Screate_simple(int rank, const hsize_t dims[], const hsize_t maxdims[])</div><div class="ttdoc">Creates a new simple dataspace and opens it for access.</div></div>
<div class="ttc" id="agroup___p_d_t_i_e_e_e_html_ga994ce9ffdd2c77a9352b102a883503ea"><div class="ttname"><a href="group___p_d_t_i_e_e_e.html#ga994ce9ffdd2c77a9352b102a883503ea">H5T_IEEE_F32LE</a></div><div class="ttdeci">#define H5T_IEEE_F32LE</div><div class="ttdef"><b>Definition:</b> H5Tpublic.h:261</div></div>
<div class="ttc" id="agroup___p_l_c_r_html_ga5dce61149211d3ef319452aa598887fb"><div class="ttname"><a href="group___p_l_c_r.html#ga5dce61149211d3ef319452aa598887fb">H5Pclose</a></div><div class="ttdeci">herr_t H5Pclose(hid_t plist_id)</div><div class="ttdoc">Terminates access to a property list.</div></div>
<div class="ttc" id="agroup___p_l_c_r_html_gaf1b11da01d4d45d788c45f8bc5f0cbfa"><div class="ttname"><a href="group___p_l_c_r.html#gaf1b11da01d4d45d788c45f8bc5f0cbfa">H5Pcreate</a></div><div class="ttdeci">hid_t H5Pcreate(hid_t cls_id)</div><div class="ttdoc">Creates a new property list as an instance of a property list class.</div></div>
</div><!-- fragment --> <dl class="section user"><dt>Discussion</dt><dd>Large attributes are supported only in HDF5 versions 1.8.x and higher. This has implications for the accessibility of your HDF5 files and is your call.<br />
Since there are no size limitations for large attributes, it might seem tempting to mistake them for dataset stand-ins. This is not the case, for at least two reasons:<ol type="1">
<li>Attributes decorate HDF5 objects, have their own local namespace, and can't be link targets.</li>
<li>Attribute I/O treats the attribute value as atomic, i.e., there is no support for partial I/O. A large attribute will always be read or written in its entirety.</li>
</ol>
</dd></dl>
<dl class="section user"><dt>See Also</dt><dd>See <a class="el" href="_accessibility.html#CB_MaintainCompat">Maintaining Compatibility with other HDF5 Library Versions</a> for HDF5 compatibility implications. </dd></dl>
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