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<a href="#groups">Topics</a> |
<a href="#func-members">Functions</a> </div>
<div class="headertitle"><div class="title">Identifiers (H5I)</div></div>
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<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<p>Use the functions in this module to manage identifiers defined by the HDF5 library. See <a class="el" href="group___h5_i_u_d.html">User-defined ID Types</a> for user-defined identifiers and identifier types.</p>
<p>HDF5 identifiers are usually created as a side-effect of creating HDF5 entities such as groups, datasets, attributes, or property lists.</p>
<p>Identifiers defined by the HDF5 library can be used to retrieve information such as path names and reference counts, and their validity can be checked.</p>
<p>Identifiers can be updated by manipulating their reference counts.</p>
<p>Unused identifiers should be reclaimed by closing the associated item, e.g., HDF5 object, or decrementing the reference count to 0.</p>
<dl class="section note"><dt>Note</dt><dd>Identifiers (of type <a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a>) are run-time auxiliaries and not persisted in the file.</dd></dl>
<table class="doxtable">
<tr>
<th>Create</th><th>Read </th></tr>
<tr valign="top">
<td><div class="fragment"><div class="line"><span class="lineno"> 15</span> {</div>
<div class="line"><span class="lineno"> 16</span> __label__ fail_dcpl;</div>
<div class="line"><span class="lineno"> 17</span> <a class="code hl_typedef" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> dcpl;</div>
<div class="line"><span class="lineno"> 18</span> </div>
<div class="line"><span class="lineno"> 19</span> <span class="comment">// create an ID of a pre-defined ID type</span></div>
<div class="line"><span class="lineno"> 20</span> <span class="keywordflow">if</span> ((dcpl = <a class="code hl_function" href="group___p_l_c_r.html#gaf1b11da01d4d45d788c45f8bc5f0cbfa">H5Pcreate</a>(<a class="code hl_define" href="_h5_ppublic_8h.html#a6f9c8a5aba72c0445fff384bf418a80d">H5P_DATASET_XFER</a>)) == <a class="code hl_define" href="_h5_ipublic_8h.html#a01eab13dccc91afd6909d74dccb780ba">H5I_INVALID_HID</a>) {</div>
<div class="line"><span class="lineno"> 21</span> ret_val = EXIT_FAILURE;</div>
<div class="line"><span class="lineno"> 22</span> <span class="keywordflow">goto</span> fail_dcpl;</div>
<div class="line"><span class="lineno"> 23</span> }</div>
<div class="line"><span class="lineno"> 24</span> </div>
<div class="line"><span class="lineno"> 25</span> <span class="comment">// we can reliably predict the ID type</span></div>
<div class="line"><span class="lineno"> 26</span> assert(<a class="code hl_function" href="#ga4941435d4d64de3d7095d2316f415f2d">H5Iget_type</a>(dcpl) == <a class="code hl_enumvalue" href="_h5_ipublic_8h.html#a13afe14178faf81b89fa2167e7ab832bab6161706783d4bca26a889f1ac0cf91a">H5I_GENPROP_LST</a>);</div>
<div class="line"><span class="lineno"> 27</span> printf(<span class="stringliteral">"%d\n"</span>, <a class="code hl_function" href="#ga4941435d4d64de3d7095d2316f415f2d">H5Iget_type</a>(dcpl));</div>
<div class="line"><span class="lineno"> 28</span> </div>
<div class="line"><span class="lineno"> 29</span> <a class="code hl_function" href="group___p_l_c_r.html#ga5dce61149211d3ef319452aa598887fb">H5Pclose</a>(dcpl);</div>
<div class="line"><span class="lineno"> 30</span>fail_dcpl:;</div>
<div class="line"><span class="lineno"> 31</span> }</div>
</div><!-- fragment --> </td><td><div class="fragment"><div class="line"><span class="lineno"> 35</span> {</div>
<div class="line"><span class="lineno"> 36</span> __label__ fail_dcpl;</div>
<div class="line"><span class="lineno"> 37</span> <a class="code hl_typedef" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> dcpl;</div>
<div class="line"><span class="lineno"> 38</span> </div>
<div class="line"><span class="lineno"> 39</span> <span class="comment">// create an ID of a pre-defined ID type</span></div>
<div class="line"><span class="lineno"> 40</span> <span class="keywordflow">if</span> ((dcpl = <a class="code hl_function" href="group___p_l_c_r.html#gaf1b11da01d4d45d788c45f8bc5f0cbfa">H5Pcreate</a>(<a class="code hl_define" href="_h5_ppublic_8h.html#a6f9c8a5aba72c0445fff384bf418a80d">H5P_DATASET_XFER</a>)) == <a class="code hl_define" href="_h5_ipublic_8h.html#a01eab13dccc91afd6909d74dccb780ba">H5I_INVALID_HID</a>) {</div>
<div class="line"><span class="lineno"> 41</span> ret_val = EXIT_FAILURE;</div>
<div class="line"><span class="lineno"> 42</span> <span class="keywordflow">goto</span> fail_dcpl;</div>
<div class="line"><span class="lineno"> 43</span> }</div>
<div class="line"><span class="lineno"> 44</span> </div>
<div class="line"><span class="lineno"> 45</span> <span class="comment">// this better be valid</span></div>
<div class="line"><span class="lineno"> 46</span> assert(<a class="code hl_function" href="#ga20eb10c559d9ed5ba6f77b31d6a3ba9a">H5Iis_valid</a>(dcpl) > 0);</div>
<div class="line"><span class="lineno"> 47</span> </div>
<div class="line"><span class="lineno"> 48</span> <span class="comment">// this ID is NOT associated with any HDF5 file;</span></div>
<div class="line"><span class="lineno"> 49</span> <span class="comment">// see the error message</span></div>
<div class="line"><span class="lineno"> 50</span> assert(<a class="code hl_function" href="#ga6ce32e88051e4cdf7d02439d86e5e042">H5Iget_file_id</a>(dcpl) == <a class="code hl_define" href="_h5_ipublic_8h.html#a01eab13dccc91afd6909d74dccb780ba">H5I_INVALID_HID</a>);</div>
<div class="line"><span class="lineno"> 51</span> </div>
<div class="line"><span class="lineno"> 52</span> <a class="code hl_function" href="group___p_l_c_r.html#ga5dce61149211d3ef319452aa598887fb">H5Pclose</a>(dcpl);</div>
<div class="line"><span class="lineno"> 53</span>fail_dcpl:;</div>
<div class="line"><span class="lineno"> 54</span> }</div>
</div><!-- fragment --> </td></tr>
<tr>
<th>Update</th><th>Delete </th></tr>
<tr valign="top">
<td><div class="fragment"><div class="line"><span class="lineno"> 58</span> {</div>
<div class="line"><span class="lineno"> 59</span> __label__ fail_rc, fail_dcpl;</div>
<div class="line"><span class="lineno"> 60</span> <a class="code hl_typedef" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> dcpl;</div>
<div class="line"><span class="lineno"> 61</span> <span class="keywordtype">int</span> rc;</div>
<div class="line"><span class="lineno"> 62</span> </div>
<div class="line"><span class="lineno"> 63</span> <span class="comment">// create an ID of a pre-defined ID type</span></div>
<div class="line"><span class="lineno"> 64</span> <span class="keywordflow">if</span> ((dcpl = <a class="code hl_function" href="group___p_l_c_r.html#gaf1b11da01d4d45d788c45f8bc5f0cbfa">H5Pcreate</a>(<a class="code hl_define" href="_h5_ppublic_8h.html#a6f9c8a5aba72c0445fff384bf418a80d">H5P_DATASET_XFER</a>)) == <a class="code hl_define" href="_h5_ipublic_8h.html#a01eab13dccc91afd6909d74dccb780ba">H5I_INVALID_HID</a>) {</div>
<div class="line"><span class="lineno"> 65</span> ret_val = EXIT_FAILURE;</div>
<div class="line"><span class="lineno"> 66</span> <span class="keywordflow">goto</span> fail_dcpl;</div>
<div class="line"><span class="lineno"> 67</span> }</div>
<div class="line"><span class="lineno"> 68</span> </div>
<div class="line"><span class="lineno"> 69</span> <span class="comment">// retrieve the IDs reference count</span></div>
<div class="line"><span class="lineno"> 70</span> <span class="keywordflow">if</span> ((rc = <a class="code hl_function" href="#gac9638ade14cc75b7b125b3723f319c81">H5Iget_ref</a>(dcpl)) < 0) {</div>
<div class="line"><span class="lineno"> 71</span> ret_val = EXIT_FAILURE;</div>
<div class="line"><span class="lineno"> 72</span> <span class="keywordflow">goto</span> fail_rc;</div>
<div class="line"><span class="lineno"> 73</span> }</div>
<div class="line"><span class="lineno"> 74</span> printf(<span class="stringliteral">"Reference count: %d\n"</span>, rc);</div>
<div class="line"><span class="lineno"> 75</span> </div>
<div class="line"><span class="lineno"> 76</span> <span class="comment">// bump its reference count (by 1)</span></div>
<div class="line"><span class="lineno"> 77</span> <span class="keywordflow">if</span> ((rc = <a class="code hl_function" href="#ga3fd0c157704573965cafd6e1aa7f368f">H5Iinc_ref</a>(dcpl)) < 0) {</div>
<div class="line"><span class="lineno"> 78</span> ret_val = EXIT_FAILURE;</div>
<div class="line"><span class="lineno"> 79</span> <span class="keywordflow">goto</span> fail_rc;</div>
<div class="line"><span class="lineno"> 80</span> }</div>
<div class="line"><span class="lineno"> 81</span> printf(<span class="stringliteral">"Reference count: %d\n"</span>, rc);</div>
<div class="line"><span class="lineno"> 82</span> </div>
<div class="line"><span class="lineno"> 83</span>fail_rc:</div>
<div class="line"><span class="lineno"> 84</span> <a class="code hl_function" href="group___p_l_c_r.html#ga5dce61149211d3ef319452aa598887fb">H5Pclose</a>(dcpl);</div>
<div class="line"><span class="lineno"> 85</span>fail_dcpl:;</div>
<div class="line"><span class="lineno"> 86</span> }</div>
</div><!-- fragment --> </td><td><div class="fragment"><div class="line"><span class="lineno"> 90</span> {</div>
<div class="line"><span class="lineno"> 91</span> __label__ fail_rc, fail_dcpl;</div>
<div class="line"><span class="lineno"> 92</span> <a class="code hl_typedef" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> dcpl;</div>
<div class="line"><span class="lineno"> 93</span> <span class="keywordtype">int</span> rc;</div>
<div class="line"><span class="lineno"> 94</span> </div>
<div class="line"><span class="lineno"> 95</span> <span class="comment">// create an ID of a pre-defined ID type</span></div>
<div class="line"><span class="lineno"> 96</span> <span class="keywordflow">if</span> ((dcpl = <a class="code hl_function" href="group___p_l_c_r.html#gaf1b11da01d4d45d788c45f8bc5f0cbfa">H5Pcreate</a>(<a class="code hl_define" href="_h5_ppublic_8h.html#a6f9c8a5aba72c0445fff384bf418a80d">H5P_DATASET_XFER</a>)) == <a class="code hl_define" href="_h5_ipublic_8h.html#a01eab13dccc91afd6909d74dccb780ba">H5I_INVALID_HID</a>) {</div>
<div class="line"><span class="lineno"> 97</span> ret_val = EXIT_FAILURE;</div>
<div class="line"><span class="lineno"> 98</span> <span class="keywordflow">goto</span> fail_dcpl;</div>
<div class="line"><span class="lineno"> 99</span> }</div>
<div class="line"><span class="lineno"> 100</span> </div>
<div class="line"><span class="lineno"> 101</span> <span class="comment">// decrease its reference count (from 1) to 0</span></div>
<div class="line"><span class="lineno"> 102</span> <span class="keywordflow">if</span> ((rc = <a class="code hl_function" href="#gaea2aa78caea892edf2a6a6ac70486ed9">H5Idec_ref</a>(dcpl)) < 0) {</div>
<div class="line"><span class="lineno"> 103</span> ret_val = EXIT_FAILURE;</div>
<div class="line"><span class="lineno"> 104</span> <span class="keywordflow">goto</span> fail_rc;</div>
<div class="line"><span class="lineno"> 105</span> }</div>
<div class="line"><span class="lineno"> 106</span> printf(<span class="stringliteral">"Reference count: %d\n"</span>, rc);</div>
<div class="line"><span class="lineno"> 107</span> </div>
<div class="line"><span class="lineno"> 108</span> <span class="comment">// at this point, the ID is no longer valid</span></div>
<div class="line"><span class="lineno"> 109</span> assert(<a class="code hl_function" href="#ga20eb10c559d9ed5ba6f77b31d6a3ba9a">H5Iis_valid</a>(dcpl) == 0);</div>
<div class="line"><span class="lineno"> 110</span> </div>
<div class="line"><span class="lineno"> 111</span> <span class="comment">// dropping the ref. count to 0 has the side-effect of closing</span></div>
<div class="line"><span class="lineno"> 112</span> <span class="comment">// the associated item, and calling H5Pclose would create an error</span></div>
<div class="line"><span class="lineno"> 113</span> <span class="keywordflow">goto</span> fail_dcpl;</div>
<div class="line"><span class="lineno"> 114</span> </div>
<div class="line"><span class="lineno"> 115</span>fail_rc:</div>
<div class="line"><span class="lineno"> 116</span> <a class="code hl_function" href="group___p_l_c_r.html#ga5dce61149211d3ef319452aa598887fb">H5Pclose</a>(dcpl);</div>
<div class="line"><span class="lineno"> 117</span>fail_dcpl:;</div>
<div class="line"><span class="lineno"> 118</span> }</div>
</div><!-- fragment --> </td></tr>
</table>
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Topics</h2></td></tr>
<tr class="memitem:group___h5_i_u_d" id="r_group___h5_i_u_d"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="group___h5_i_u_d.html">User-defined ID Types</a></td></tr>
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Functions</h2></td></tr>
<tr class="memitem:gad61703cd16f392fb194da648099e69a9" id="r_gad61703cd16f392fb194da648099e69a9"><td class="memItemLeft" align="right" valign="top"><a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="#gad61703cd16f392fb194da648099e69a9">H5Iregister_future</a> (<a class="el" href="_h5_ipublic_8h.html#a13afe14178faf81b89fa2167e7ab832b">H5I_type_t</a> type, const void *object, <a class="el" href="_h5_idevelop_8h.html#ab0f349ec701c3d8c6ded067f160da44c">H5I_future_realize_func_t</a> realize_cb, <a class="el" href="_h5_idevelop_8h.html#a127fbac3b8283a7804d8470676a65518">H5I_future_discard_func_t</a> discard_cb)</td></tr>
<tr class="memdesc:gad61703cd16f392fb194da648099e69a9"><td class="mdescLeft"> </td><td class="mdescRight">Registers a "future" object under a type and returns an ID for it. <br /></td></tr>
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<tr class="memitem:ga4941435d4d64de3d7095d2316f415f2d" id="r_ga4941435d4d64de3d7095d2316f415f2d"><td class="memItemLeft" align="right" valign="top"><a class="el" href="_h5_ipublic_8h.html#a13afe14178faf81b89fa2167e7ab832b">H5I_type_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="#ga4941435d4d64de3d7095d2316f415f2d">H5Iget_type</a> (<a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> id)</td></tr>
<tr class="memdesc:ga4941435d4d64de3d7095d2316f415f2d"><td class="mdescLeft"> </td><td class="mdescRight">Retrieves the type of an object. <br /></td></tr>
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<tr class="memitem:ga6ce32e88051e4cdf7d02439d86e5e042" id="r_ga6ce32e88051e4cdf7d02439d86e5e042"><td class="memItemLeft" align="right" valign="top"><a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="#ga6ce32e88051e4cdf7d02439d86e5e042">H5Iget_file_id</a> (<a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> id)</td></tr>
<tr class="memdesc:ga6ce32e88051e4cdf7d02439d86e5e042"><td class="mdescLeft"> </td><td class="mdescRight">Retrieves an identifier for the file containing the specified object. <br /></td></tr>
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<tr class="memitem:ga9c84a8dc29566b82b6d1ff7a6e6828f1" id="r_ga9c84a8dc29566b82b6d1ff7a6e6828f1"><td class="memItemLeft" align="right" valign="top"><a class="el" href="_h5public_8h.html#af629ed855824cf5955b54529adf78ad6">ssize_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="#ga9c84a8dc29566b82b6d1ff7a6e6828f1">H5Iget_name</a> (<a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> id, char *name, size_t size)</td></tr>
<tr class="memdesc:ga9c84a8dc29566b82b6d1ff7a6e6828f1"><td class="mdescLeft"> </td><td class="mdescRight">Retrieves a name of an object based on the object identifier. <br /></td></tr>
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<tr class="memitem:ga3fd0c157704573965cafd6e1aa7f368f" id="r_ga3fd0c157704573965cafd6e1aa7f368f"><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="#ga3fd0c157704573965cafd6e1aa7f368f">H5Iinc_ref</a> (<a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> id)</td></tr>
<tr class="memdesc:ga3fd0c157704573965cafd6e1aa7f368f"><td class="mdescLeft"> </td><td class="mdescRight">Increments the reference count for an object. <br /></td></tr>
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<tr class="memitem:gaea2aa78caea892edf2a6a6ac70486ed9" id="r_gaea2aa78caea892edf2a6a6ac70486ed9"><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="#gaea2aa78caea892edf2a6a6ac70486ed9">H5Idec_ref</a> (<a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> id)</td></tr>
<tr class="memdesc:gaea2aa78caea892edf2a6a6ac70486ed9"><td class="mdescLeft"> </td><td class="mdescRight">Decrements the reference count for an object. <br /></td></tr>
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<tr class="memitem:gac9638ade14cc75b7b125b3723f319c81" id="r_gac9638ade14cc75b7b125b3723f319c81"><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="#gac9638ade14cc75b7b125b3723f319c81">H5Iget_ref</a> (<a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> id)</td></tr>
<tr class="memdesc:gac9638ade14cc75b7b125b3723f319c81"><td class="mdescLeft"> </td><td class="mdescRight">Retrieves the reference count for an object. <br /></td></tr>
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<tr class="memitem:ga20eb10c559d9ed5ba6f77b31d6a3ba9a" id="r_ga20eb10c559d9ed5ba6f77b31d6a3ba9a"><td class="memItemLeft" align="right" valign="top"><a class="el" href="_h5public_8h.html#aa8f6c28736dbd0f18388c67911d38aca">htri_t</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="#ga20eb10c559d9ed5ba6f77b31d6a3ba9a">H5Iis_valid</a> (<a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> id)</td></tr>
<tr class="memdesc:ga20eb10c559d9ed5ba6f77b31d6a3ba9a"><td class="mdescLeft"> </td><td class="mdescRight">Determines whether an identifier is valid. <br /></td></tr>
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<h2 class="groupheader">Function Documentation</h2>
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<h2 class="memtitle"><span class="permalink"><a href="#gaea2aa78caea892edf2a6a6ac70486ed9">◆ </a></span>H5Idec_ref()</h2>
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<td class="memname">int H5Idec_ref </td>
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<p>Decrements the reference count for an object. </p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">id</td><td>Object identifier</td></tr>
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<dl class="section return"><dt>Returns</dt><dd>Returns a non-negative reference count of the object ID after decrementing it, if successful; otherwise a negative value is returned.</dd></dl>
<p><a class="el" href="#gaea2aa78caea892edf2a6a6ac70486ed9" title="Decrements the reference count for an object.">H5Idec_ref()</a> decrements the reference count of the object identified by <code>id</code>.</p>
<p>The reference count for an object ID is attached to the information about an object in memory and has no relation to the number of links to an object on disk.</p>
<p>The reference count for a newly created object will be 1. Reference counts for objects may be explicitly modified with this function or with <a class="el" href="#ga3fd0c157704573965cafd6e1aa7f368f" title="Increments the reference count for an object.">H5Iinc_ref()</a>. When an object identifier's reference count reaches zero, the object will be closed. Calling an object identifier's <code>close</code> function decrements the reference count for the identifier, which normally closes the object, but if the reference count for the identifier has been incremented with <a class="el" href="#ga3fd0c157704573965cafd6e1aa7f368f" title="Increments the reference count for an object.">H5Iinc_ref()</a>, the object will only be closed when the reference count reaches zero with further calls to this function or the object identifier's <code>close</code> function.</p>
<p>If the object ID was created by a collective parallel call (such as <a class="el" href="group___h5_d.html#ga0647ba4bbd26d5230cc07f3a5685b2cf">H5Dcreate()</a>, <a class="el" href="group___h5_g.html#ga3eca6807deff4f9e51fc5fe0befc2245">H5Gopen()</a>, etc.), the reference count should be modified by all the processes which have copies of the ID. Generally, this means that group, dataset, attribute, file and named datatype IDs should be modified by all the processes and that all other types of IDs are safe to modify by individual processes.</p>
<p>This function is of particular value when an application maintains multiple copies of an object ID. The object ID can be incremented when a copy is made. Each copy of the ID can then be safely closed or decremented and the HDF5 object will be closed when the reference count for that object drops to zero.</p>
<dl class="section since"><dt>Since</dt><dd>1.6.3 </dd></dl>
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<h2 class="memtitle"><span class="permalink"><a href="#ga6ce32e88051e4cdf7d02439d86e5e042">◆ </a></span>H5Iget_file_id()</h2>
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<td class="memname"><a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> H5Iget_file_id </td>
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<p>Retrieves an identifier for the file containing the specified object. </p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">id</td><td>Object identifier</td></tr>
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<dl class="section return"><dt>Returns</dt><dd>Returns a file identifier if successful; otherwise returns <a class="el" href="_h5_ipublic_8h.html#a01eab13dccc91afd6909d74dccb780ba">H5I_INVALID_HID</a>.</dd></dl>
<p><a class="el" href="#ga6ce32e88051e4cdf7d02439d86e5e042" title="Retrieves an identifier for the file containing the specified object.">H5Iget_file_id()</a> returns the identifier of the file associated with the object referenced by <code>id</code>.</p>
<dl class="section note"><dt>Note</dt><dd>Note that the HDF5 library permits an application to close a file while objects within the file remain open. If the file containing the object <code>id</code> is still open, <a class="el" href="#ga6ce32e88051e4cdf7d02439d86e5e042" title="Retrieves an identifier for the file containing the specified object.">H5Iget_file_id()</a> will retrieve the existing file identifier. If there is no existing file identifier for the file, i.e., the file has been closed, <a class="el" href="#ga6ce32e88051e4cdf7d02439d86e5e042" title="Retrieves an identifier for the file containing the specified object.">H5Iget_file_id()</a> will reopen the file and return a new file identifier. In either case, the file identifier must eventually be released using <a class="el" href="group___h5_f.html#gac55cd91d80822e4f8c2a7f04ea71b124" title="Terminates access to an HDF5 file.">H5Fclose()</a>.</dd></dl>
<dl class="section since"><dt>Since</dt><dd>1.6.3 </dd></dl>
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<h2 class="memtitle"><span class="permalink"><a href="#ga9c84a8dc29566b82b6d1ff7a6e6828f1">◆ </a></span>H5Iget_name()</h2>
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<td class="memname"><a class="el" href="_h5public_8h.html#af629ed855824cf5955b54529adf78ad6">ssize_t</a> H5Iget_name </td>
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<td class="paramtype"><a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a></td> <td class="paramname"><span class="paramname"><em>id</em>, </span></td>
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<p>Retrieves a name of an object based on the object identifier. </p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">id</td><td>Object identifier </td></tr>
<tr><td class="paramdir">[out]</td><td class="paramname">name</td><td>A buffer for the name associated with the identifier </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">size</td><td>The size of the <code>name</code> buffer; usually the size of the name in bytes plus 1 for a NULL terminator</td></tr>
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<dl class="section return"><dt>Returns</dt><dd>ssize_t</dd></dl>
<p><a class="el" href="#ga9c84a8dc29566b82b6d1ff7a6e6828f1" title="Retrieves a name of an object based on the object identifier.">H5Iget_name()</a> retrieves a name for the object identified by <code>id</code>.</p>
<p>Up to size characters of the name are returned in <code>name</code>; additional characters, if any, are not returned to the user application.</p>
<p>If the length of the name, which determines the required value of <code>size</code>, is unknown, a preliminary <a class="el" href="#ga9c84a8dc29566b82b6d1ff7a6e6828f1" title="Retrieves a name of an object based on the object identifier.">H5Iget_name()</a> call can be made. The return value of this call will be the size in bytes of the object name. That value, plus 1 for a NULL terminator, is then assigned to size for a second <a class="el" href="#ga9c84a8dc29566b82b6d1ff7a6e6828f1" title="Retrieves a name of an object based on the object identifier.">H5Iget_name()</a> call, which will retrieve the actual name.</p>
<p>If the object identified by <code>id</code> is an attribute, as determined via <a class="el" href="#ga4941435d4d64de3d7095d2316f415f2d" title="Retrieves the type of an object.">H5Iget_type()</a>, <a class="el" href="#ga9c84a8dc29566b82b6d1ff7a6e6828f1" title="Retrieves a name of an object based on the object identifier.">H5Iget_name()</a> retrieves the name of the object to which that attribute is attached. To retrieve the name of the attribute itself, use <a class="el" href="group___h5_a.html#ga05e195aabab8c623b1c52009aeb99674" title="Gets an attribute name.">H5Aget_name()</a>.</p>
<p>If there is no name associated with the object identifier or if the name is NULL, <a class="el" href="#ga9c84a8dc29566b82b6d1ff7a6e6828f1" title="Retrieves a name of an object based on the object identifier.">H5Iget_name()</a> returns 0 (zero).</p>
<dl class="section note"><dt>Note</dt><dd>Note that an object in an HDF5 file may have multiple paths if there are multiple links pointing to it. This function may return any one of these paths. When possible, <a class="el" href="#ga9c84a8dc29566b82b6d1ff7a6e6828f1" title="Retrieves a name of an object based on the object identifier.">H5Iget_name()</a> returns the path with which the object was opened.</dd></dl>
<dl class="section since"><dt>Since</dt><dd>1.6.0 </dd></dl>
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<h2 class="memtitle"><span class="permalink"><a href="#gac9638ade14cc75b7b125b3723f319c81">◆ </a></span>H5Iget_ref()</h2>
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<td class="memname">int H5Iget_ref </td>
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<td class="paramtype"><a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a></td> <td class="paramname"><span class="paramname"><em>id</em></span></td><td>)</td>
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<p>Retrieves the reference count for an object. </p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">id</td><td>Object identifier</td></tr>
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<dl class="section return"><dt>Returns</dt><dd>Returns a non-negative current reference count of the object identifier if successful; otherwise a negative value is returned.</dd></dl>
<p><a class="el" href="#gac9638ade14cc75b7b125b3723f319c81" title="Retrieves the reference count for an object.">H5Iget_ref()</a> retrieves the reference count of the object identified by <code>id</code>.</p>
<p>The reference count for an object identifier is attached to the information about an object in memory and has no relation to the number of links to an object on disk.</p>
<p>The function <a class="el" href="#ga20eb10c559d9ed5ba6f77b31d6a3ba9a" title="Determines whether an identifier is valid.">H5Iis_valid()</a> is used to determine whether a specific object identifier is valid.</p>
<dl class="section since"><dt>Since</dt><dd>1.6.3 </dd></dl>
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<h2 class="memtitle"><span class="permalink"><a href="#ga4941435d4d64de3d7095d2316f415f2d">◆ </a></span>H5Iget_type()</h2>
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<td class="memname"><a class="el" href="_h5_ipublic_8h.html#a13afe14178faf81b89fa2167e7ab832b">H5I_type_t</a> H5Iget_type </td>
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<p>Retrieves the type of an object. </p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">id</td><td>Object identifier</td></tr>
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<dl class="section return"><dt>Returns</dt><dd>Returns the object type if successful; otherwise <a class="el" href="_h5_ipublic_8h.html#a13afe14178faf81b89fa2167e7ab832ba3e61c9654de6398dc9676ad37cbe6133">H5I_BADID</a>.</dd></dl>
<p><a class="el" href="#ga4941435d4d64de3d7095d2316f415f2d" title="Retrieves the type of an object.">H5Iget_type()</a> retrieves the type of the object identified by <code>id</code>. If no valid type can be determined or the identifier submitted is invalid, the function returns <a class="el" href="_h5_ipublic_8h.html#a13afe14178faf81b89fa2167e7ab832ba3e61c9654de6398dc9676ad37cbe6133">H5I_BADID</a>.</p>
<p>This function is of particular use in determining the type of object closing function (<a class="el" href="group___h5_d.html#gae47c3f38db49db127faf221624c30609" title="Closes the specified dataset.">H5Dclose()</a>, <a class="el" href="group___h5_g.html#ga8dbe20b390d2504f0bd3589ed8f4e221" title="Closes the specified group.">H5Gclose()</a>, etc.) to call after a call to <a class="el" href="group___h5_r.html#ga5dc19b9d1833af66c5e1f819f2c05c4a">H5Rdereference()</a>.</p>
<dl class="section note"><dt>Note</dt><dd>Note that this function returns only the type of object that <code>id</code> would identify if it were valid; it does not determine whether <code>id</code> is valid identifier. Validity can be determined with a call to <a class="el" href="#ga20eb10c559d9ed5ba6f77b31d6a3ba9a" title="Determines whether an identifier is valid.">H5Iis_valid()</a>.</dd></dl>
<dl class="section since"><dt>Since</dt><dd>1.0.0 </dd></dl>
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<h2 class="memtitle"><span class="permalink"><a href="#ga3fd0c157704573965cafd6e1aa7f368f">◆ </a></span>H5Iinc_ref()</h2>
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<td class="memname">int H5Iinc_ref </td>
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<p>Increments the reference count for an object. </p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">id</td><td>Object identifier</td></tr>
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<dl class="section return"><dt>Returns</dt><dd>Returns a non-negative reference count of the object ID after incrementing it if successful; otherwise a negative value is returned.</dd></dl>
<p><a class="el" href="#ga3fd0c157704573965cafd6e1aa7f368f" title="Increments the reference count for an object.">H5Iinc_ref()</a> increments the reference count of the object identified by <code>id</code>.</p>
<p>The reference count for an object ID is attached to the information about an object in memory and has no relation to the number of links to an object on disk.</p>
<p>The reference count for a newly created object will be 1. Reference counts for objects may be explicitly modified with this function or with <a class="el" href="#gaea2aa78caea892edf2a6a6ac70486ed9" title="Decrements the reference count for an object.">H5Idec_ref()</a>. When an object ID's reference count reaches zero, the object will be closed. Calling an object ID's <code>close</code> function decrements the reference count for the ID which normally closes the object, but if the reference count for the ID has been incremented with this function, the object will only be closed when the reference count reaches zero with further calls to <a class="el" href="#gaea2aa78caea892edf2a6a6ac70486ed9" title="Decrements the reference count for an object.">H5Idec_ref()</a> or the object ID's <code>close</code> function.</p>
<p>If the object ID was created by a collective parallel call (such as <a class="el" href="group___h5_d.html#ga0647ba4bbd26d5230cc07f3a5685b2cf">H5Dcreate()</a>, <a class="el" href="group___h5_g.html#ga3eca6807deff4f9e51fc5fe0befc2245">H5Gopen()</a>, etc.), the reference count should be modified by all the processes which have copies of the ID. Generally this means that group, dataset, attribute, file and named datatype IDs should be modified by all the processes and that all other types of IDs are safe to modify by individual processes.</p>
<p>This function is of particular value when an application is maintaining multiple copies of an object ID. The object ID can be incremented when a copy is made. Each copy of the ID can then be safely closed or decremented and the HDF5 object will be closed when the reference count for that that object drops to zero.</p>
<dl class="section since"><dt>Since</dt><dd>1.6.3 </dd></dl>
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<h2 class="memtitle"><span class="permalink"><a href="#ga20eb10c559d9ed5ba6f77b31d6a3ba9a">◆ </a></span>H5Iis_valid()</h2>
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<td class="memname"><a class="el" href="_h5public_8h.html#aa8f6c28736dbd0f18388c67911d38aca">htri_t</a> H5Iis_valid </td>
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<td class="paramtype"><a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a></td> <td class="paramname"><span class="paramname"><em>id</em></span></td><td>)</td>
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<p>Determines whether an identifier is valid. </p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">id</td><td>Object identifier</td></tr>
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<dl class="section return"><dt>Returns</dt><dd>Returns zero (false), a positive (true) or a negative (failure) value.</dd></dl>
<p><a class="el" href="#ga20eb10c559d9ed5ba6f77b31d6a3ba9a" title="Determines whether an identifier is valid.">H5Iis_valid()</a> determines whether the identifier <code>id</code> is valid.</p>
<p>Valid identifiers are those that have been obtained by an application and can still be used to access the original target. Examples of invalid identifiers include: </p><ul>
<li>Out-of-range values: negative, for example </li>
<li>Previously-valid identifiers that have been released: for example, a dataset identifier for which the dataset has been closed</li>
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<p><a class="el" href="#ga20eb10c559d9ed5ba6f77b31d6a3ba9a" title="Determines whether an identifier is valid.">H5Iis_valid()</a> can be used with any type of identifier: object identifier, property list identifier, attribute identifier, error message identifier, etc. When necessary, a call to <a class="el" href="#ga4941435d4d64de3d7095d2316f415f2d" title="Retrieves the type of an object.">H5Iget_type()</a> can determine the type of object that the <code>id</code> identifies.</p>
<dl class="section since"><dt>Since</dt><dd>1.8.3 </dd></dl>
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<h2 class="memtitle"><span class="permalink"><a href="#gad61703cd16f392fb194da648099e69a9">◆ </a></span>H5Iregister_future()</h2>
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<td class="memname"><a class="el" href="_h5_ipublic_8h.html#a0045db7ff9c22ad35db6ae91662e1943">hid_t</a> H5Iregister_future </td>
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<td class="paramtype"><a class="el" href="_h5_ipublic_8h.html#a13afe14178faf81b89fa2167e7ab832b">H5I_type_t</a></td> <td class="paramname"><span class="paramname"><em>type</em>, </span></td>
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<td class="paramtype"><a class="el" href="_h5_idevelop_8h.html#ab0f349ec701c3d8c6ded067f160da44c">H5I_future_realize_func_t</a></td> <td class="paramname"><span class="paramname"><em>realize_cb</em>, </span></td>
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<td class="paramtype"><a class="el" href="_h5_idevelop_8h.html#a127fbac3b8283a7804d8470676a65518">H5I_future_discard_func_t</a></td> <td class="paramname"><span class="paramname"><em>discard_cb</em></span> )</td>
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<p>Registers a "future" object under a type and returns an ID for it. </p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramdir">[in]</td><td class="paramname">type</td><td>The identifier of the type of the new ID </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">object</td><td>Pointer to "future" object for which a new ID is created </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">realize_cb</td><td>Function pointer to realize a future object </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">discard_cb</td><td>Function pointer to destroy a future object</td></tr>
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<dl class="section return"><dt>Returns</dt><dd>Returns a object identifier if successful; otherwise returns <a class="el" href="_h5_ipublic_8h.html#a01eab13dccc91afd6909d74dccb780ba">H5I_INVALID_HID</a>.</dd></dl>
<p><a class="el" href="#gad61703cd16f392fb194da648099e69a9" title="Registers a "future" object under a type and returns an ID for it.">H5Iregister_future()</a> creates and returns a new ID for a "future" object. Future objects are a special kind of object and represent a placeholder for an object that has not yet been created or opened. The <code>realize_cb</code> will be invoked by the HDF5 library to 'realize' the future object as an actual object. A call to <a class="el" href="group___h5_i_u_d.html#ga82b68eac53ed4c55efd98ab4d0eb9035" title="Returns the object referenced by an ID.">H5Iobject_verify()</a> will invoke the <code>realize_cb</code> callback and if it successfully returns, will return the actual object, not the future object.</p>
<p>The <code>type</code> parameter is the identifier for the ID type to which this new future ID will belong. This identifier may have been created by a call to <a class="el" href="group___h5_i_u_d.html#gae10d4baa1335b2d1f1aecffb305e1613" title="Creates and returns a new ID type.">H5Iregister_type()</a> or may be one of the HDF5 pre-defined ID classes (e.g. H5I_FILE, H5I_GROUP, H5I_DATASPACE, etc).</p>
<p>The <code>object</code> parameter is a pointer to the memory which the new ID will be a reference to. This pointer will be stored by the library, but will not be returned to a call to <a class="el" href="group___h5_i_u_d.html#ga82b68eac53ed4c55efd98ab4d0eb9035" title="Returns the object referenced by an ID.">H5Iobject_verify()</a> until the <code>realize_cb</code> callback has returned the actual pointer for the object.</p>
<p>A NULL value for <code>object</code> is allowed.</p>
<p>The <code>realize_cb</code> parameter is a function pointer that will be invoked by the HDF5 library to convert a future object into an actual object. The <code>realize_cb</code> function may be invoked by <a class="el" href="group___h5_i_u_d.html#ga82b68eac53ed4c55efd98ab4d0eb9035" title="Returns the object referenced by an ID.">H5Iobject_verify()</a> to return the actual object for a user-defined ID class (i.e. an ID class registered with <a class="el" href="group___h5_i_u_d.html#gae10d4baa1335b2d1f1aecffb305e1613" title="Creates and returns a new ID type.">H5Iregister_type()</a>) or internally by the HDF5 library in order to use or get information from an HDF5 pre-defined ID type. For example, the <code>realize_cb</code> for a future dataspace object will be called during the process of returning information from <a class="el" href="group___h5_s.html#gac494409b615d8e67c5edd9eb2848b2f3" title="Retrieves dataspace dimension size and maximum size.">H5Sget_simple_extent_dims()</a>.</p>
<p>Note that although the <code>realize_cb</code> routine returns an ID (as a parameter) for the actual object, the HDF5 library will swap the actual object in that ID for the future object in the future ID. This ensures that the ID value for the object doesn't change for the user when the object is realized.</p>
<p>Note that the <code>realize_cb</code> callback could receive a NULL value for a future object pointer, if one was used when <a class="el" href="#gad61703cd16f392fb194da648099e69a9" title="Registers a "future" object under a type and returns an ID for it.">H5Iregister_future()</a> was initially called. This is permitted as a means of allowing the <code>realize_cb</code> to act as a generator of new objects, without requiring creation of unnecessary future objects.</p>
<p>It is an error to pass NULL for <code>realize_cb</code>.</p>
<p>The <code>discard_cb</code> parameter is a function pointer that will be invoked by the HDF5 library to destroy a future object. This callback will always be invoked for <em>every</em> future object, whether the <code>realize_cb</code> is invoked on it or not. It's possible that the <code>discard_cb</code> is invoked on a future object without the <code>realize_cb</code> being invoked, e.g. when a future ID is closed without requiring the future object to be realized into an actual one.</p>
<p>Note that the <code>discard_cb</code> callback could receive a NULL value for a future object pointer, if one was used when <a class="el" href="#gad61703cd16f392fb194da648099e69a9" title="Registers a "future" object under a type and returns an ID for it.">H5Iregister_future()</a> was initially called.</p>
<p>It is an error to pass NULL for <code>discard_cb</code>.</p>
<dl class="section note"><dt>Note</dt><dd>The <a class="el" href="#gad61703cd16f392fb194da648099e69a9" title="Registers a "future" object under a type and returns an ID for it.">H5Iregister_future()</a> function is primarily targeted at VOL connector authors and is <em>not</em> designed for general-purpose application use.</dd></dl>
<dl class="section since"><dt>Since</dt><dd>1.14.0 </dd></dl>
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