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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<li class="navelem"><b>mysqlpp</b></li><li class="navelem"><a class="el" href="classmysqlpp_1_1Null.html">Null</a></li> </ul>
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<div class="header">
<div class="summary">
<a href="#pub-types">Public Types</a> |
<a href="#pub-methods">Public Member Functions</a> |
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<a href="classmysqlpp_1_1Null-members.html">List of all members</a> </div>
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<div class="title">mysqlpp::Null< Type, Behavior > Class Template Reference</div> </div>
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<p>Class for holding data from a SQL column with the NULL attribute.
<a href="classmysqlpp_1_1Null.html#details">More...</a></p>
<p><code>#include <<a class="el" href="null_8h_source.html">null.h</a>></code></p>
<table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="pub-types"></a>
Public Types</h2></td></tr>
<tr class="memitem:aca01e95f7308d0601463e941857245ac"><td class="memItemLeft" align="right" valign="top"><a id="aca01e95f7308d0601463e941857245ac"></a>
typedef Type </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#aca01e95f7308d0601463e941857245ac">value_type</a></td></tr>
<tr class="memdesc:aca01e95f7308d0601463e941857245ac"><td class="mdescLeft"> </td><td class="mdescRight">Type of the data stored in this object, when it is not equal to SQL null. <br /></td></tr>
<tr class="separator:aca01e95f7308d0601463e941857245ac"><td class="memSeparator" colspan="2"> </td></tr>
</table><table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="pub-methods"></a>
Public Member Functions</h2></td></tr>
<tr class="memitem:aa776139d049ac32aa7850ecd5e623b8f"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#aa776139d049ac32aa7850ecd5e623b8f">Null</a> ()</td></tr>
<tr class="memdesc:aa776139d049ac32aa7850ecd5e623b8f"><td class="mdescLeft"> </td><td class="mdescRight">Default constructor. <a href="#aa776139d049ac32aa7850ecd5e623b8f">More...</a><br /></td></tr>
<tr class="separator:aa776139d049ac32aa7850ecd5e623b8f"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a738398c6aa00bd5a4d691f6277e453ca"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#a738398c6aa00bd5a4d691f6277e453ca">Null</a> (const Type &x)</td></tr>
<tr class="memdesc:a738398c6aa00bd5a4d691f6277e453ca"><td class="mdescLeft"> </td><td class="mdescRight">Initialize the object with a particular value. <a href="#a738398c6aa00bd5a4d691f6277e453ca">More...</a><br /></td></tr>
<tr class="separator:a738398c6aa00bd5a4d691f6277e453ca"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:ab04ae6dc7e0e4ad80021014a6e241b67"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#ab04ae6dc7e0e4ad80021014a6e241b67">Null</a> (const <a class="el" href="classmysqlpp_1_1null__type.html">null_type</a> &)</td></tr>
<tr class="memdesc:ab04ae6dc7e0e4ad80021014a6e241b67"><td class="mdescLeft"> </td><td class="mdescRight">Construct a <a class="el" href="classmysqlpp_1_1Null.html" title="Class for holding data from a SQL column with the NULL attribute.">Null</a> equal to SQL null. <a href="#ab04ae6dc7e0e4ad80021014a6e241b67">More...</a><br /></td></tr>
<tr class="separator:ab04ae6dc7e0e4ad80021014a6e241b67"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a2ff8415d7070ebbe0462dd78f278d78a"><td class="memItemLeft" align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#a2ff8415d7070ebbe0462dd78f278d78a">operator Type</a> () const</td></tr>
<tr class="memdesc:a2ff8415d7070ebbe0462dd78f278d78a"><td class="mdescLeft"> </td><td class="mdescRight">Converts this object to Type. <a href="#a2ff8415d7070ebbe0462dd78f278d78a">More...</a><br /></td></tr>
<tr class="separator:a2ff8415d7070ebbe0462dd78f278d78a"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a166ecaa4b711982efe2d8ceee57cd06a"><td class="memItemLeft" align="right" valign="top"><a class="el" href="classmysqlpp_1_1Null.html">Null</a> & </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#a166ecaa4b711982efe2d8ceee57cd06a">operator=</a> (const Type &x)</td></tr>
<tr class="memdesc:a166ecaa4b711982efe2d8ceee57cd06a"><td class="mdescLeft"> </td><td class="mdescRight">Assign a value to the object. <a href="#a166ecaa4b711982efe2d8ceee57cd06a">More...</a><br /></td></tr>
<tr class="separator:a166ecaa4b711982efe2d8ceee57cd06a"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a05b4d11b4ac5bfa80c2a05cbcc740d01"><td class="memItemLeft" align="right" valign="top"><a class="el" href="classmysqlpp_1_1Null.html">Null</a> & </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#a05b4d11b4ac5bfa80c2a05cbcc740d01">operator=</a> (const <a class="el" href="classmysqlpp_1_1null__type.html">null_type</a> &)</td></tr>
<tr class="memdesc:a05b4d11b4ac5bfa80c2a05cbcc740d01"><td class="mdescLeft"> </td><td class="mdescRight">Assign SQL null to this object. <a href="#a05b4d11b4ac5bfa80c2a05cbcc740d01">More...</a><br /></td></tr>
<tr class="separator:a05b4d11b4ac5bfa80c2a05cbcc740d01"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:accd1446f726c245aa894e21a527612d8"><td class="memItemLeft" align="right" valign="top">bool </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#accd1446f726c245aa894e21a527612d8">operator==</a> (const <a class="el" href="classmysqlpp_1_1Null.html">Null</a>< Type > &rhs) const</td></tr>
<tr class="memdesc:accd1446f726c245aa894e21a527612d8"><td class="mdescLeft"> </td><td class="mdescRight">Do equality comparison of two nullable values. <a href="#accd1446f726c245aa894e21a527612d8">More...</a><br /></td></tr>
<tr class="separator:accd1446f726c245aa894e21a527612d8"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a86e89a86b33184fe32d3f72e5b504fe3"><td class="memItemLeft" align="right" valign="top">bool </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#a86e89a86b33184fe32d3f72e5b504fe3">operator==</a> (const <a class="el" href="classmysqlpp_1_1null__type.html">null_type</a> &) const</td></tr>
<tr class="memdesc:a86e89a86b33184fe32d3f72e5b504fe3"><td class="mdescLeft"> </td><td class="mdescRight">Do equality comparison against hard-coded SQL null. <a href="#a86e89a86b33184fe32d3f72e5b504fe3">More...</a><br /></td></tr>
<tr class="separator:a86e89a86b33184fe32d3f72e5b504fe3"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a823d1fa51de4dcdc8d0c1a3903a4ac1c"><td class="memItemLeft" align="right" valign="top"><a id="a823d1fa51de4dcdc8d0c1a3903a4ac1c"></a>
bool </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#a823d1fa51de4dcdc8d0c1a3903a4ac1c">operator !=</a> (const <a class="el" href="classmysqlpp_1_1Null.html">Null</a>< Type > &rhs) const</td></tr>
<tr class="memdesc:a823d1fa51de4dcdc8d0c1a3903a4ac1c"><td class="mdescLeft"> </td><td class="mdescRight">Do inequality comparison of two nullable values. <br /></td></tr>
<tr class="separator:a823d1fa51de4dcdc8d0c1a3903a4ac1c"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a7c8a8fe7c716ada83ef1e9fcd2657754"><td class="memItemLeft" align="right" valign="top"><a id="a7c8a8fe7c716ada83ef1e9fcd2657754"></a>
bool </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#a7c8a8fe7c716ada83ef1e9fcd2657754">operator !=</a> (const <a class="el" href="classmysqlpp_1_1null__type.html">null_type</a> &rhs) const</td></tr>
<tr class="memdesc:a7c8a8fe7c716ada83ef1e9fcd2657754"><td class="mdescLeft"> </td><td class="mdescRight">Do inequality comparison against hard-coded SQL null. <br /></td></tr>
<tr class="separator:a7c8a8fe7c716ada83ef1e9fcd2657754"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:ae7209f1af6f37a583f914bc616ea64ab"><td class="memItemLeft" align="right" valign="top">bool </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#ae7209f1af6f37a583f914bc616ea64ab">operator<</a> (const <a class="el" href="classmysqlpp_1_1Null.html">Null</a>< Type > &rhs) const</td></tr>
<tr class="memdesc:ae7209f1af6f37a583f914bc616ea64ab"><td class="mdescLeft"> </td><td class="mdescRight">Do less-than comparison of two nullable values. <a href="#ae7209f1af6f37a583f914bc616ea64ab">More...</a><br /></td></tr>
<tr class="separator:ae7209f1af6f37a583f914bc616ea64ab"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:af52c81541d4ee25a3c09399a5f402698"><td class="memItemLeft" align="right" valign="top">bool </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#af52c81541d4ee25a3c09399a5f402698">operator<</a> (const <a class="el" href="classmysqlpp_1_1null__type.html">null_type</a> &) const</td></tr>
<tr class="memdesc:af52c81541d4ee25a3c09399a5f402698"><td class="mdescLeft"> </td><td class="mdescRight">Do less-than comparison against hard-coded SQL null. <a href="#af52c81541d4ee25a3c09399a5f402698">More...</a><br /></td></tr>
<tr class="separator:af52c81541d4ee25a3c09399a5f402698"><td class="memSeparator" colspan="2"> </td></tr>
</table><table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="pub-attribs"></a>
Public Attributes</h2></td></tr>
<tr class="memitem:a11c562b34e0f4f39f34cd36ace40c33e"><td class="memItemLeft" align="right" valign="top"><a id="a11c562b34e0f4f39f34cd36ace40c33e"></a>
Type </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#a11c562b34e0f4f39f34cd36ace40c33e">data</a></td></tr>
<tr class="memdesc:a11c562b34e0f4f39f34cd36ace40c33e"><td class="mdescLeft"> </td><td class="mdescRight">The object's value, when it is not SQL null. <br /></td></tr>
<tr class="separator:a11c562b34e0f4f39f34cd36ace40c33e"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a2ce81045c6da00302bb3c998527aab7b"><td class="memItemLeft" align="right" valign="top">bool </td><td class="memItemRight" valign="bottom"><a class="el" href="classmysqlpp_1_1Null.html#a2ce81045c6da00302bb3c998527aab7b">is_null</a></td></tr>
<tr class="memdesc:a2ce81045c6da00302bb3c998527aab7b"><td class="mdescLeft"> </td><td class="mdescRight">If set, this object is considered equal to SQL null. <a href="#a2ce81045c6da00302bb3c998527aab7b">More...</a><br /></td></tr>
<tr class="separator:a2ce81045c6da00302bb3c998527aab7b"><td class="memSeparator" colspan="2"> </td></tr>
</table>
<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><h3>template<class Type, class Behavior = NullIsNull><br />
class mysqlpp::Null< Type, Behavior ></h3>
<p>Class for holding data from a SQL column with the NULL attribute. </p>
<p>This template is necessary because there is nothing in the C++ type system with the same semantics as SQL's null. In SQL, a column can have the optional 'NULL' attribute, so there is a difference in type between, say an <code>int</code> column that can be null and one that cannot be. C++'s NULL constant does not have these features.</p>
<p>It's important to realize that this class doesn't hold nulls, it holds data that <em>can</em> <em>be</em> null. It can hold a non-null value, you can then assign null to it (using MySQL++'s global <code>null</code> object), and then assign a regular value to it again; the object will behave as you expect throughout this process.</p>
<p>Because one of the template parameters is a C++ type, the typeid() for a null <code>int</code> is different than for a null <code>string</code>, to pick two random examples. See type_info.cpp for the table SQL types that can be null. </p>
</div><h2 class="groupheader">Constructor & Destructor Documentation</h2>
<a id="aa776139d049ac32aa7850ecd5e623b8f"></a>
<h2 class="memtitle"><span class="permalink"><a href="#aa776139d049ac32aa7850ecd5e623b8f">◆ </a></span>Null() <span class="overload">[1/3]</span></h2>
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template<class Type, class Behavior = NullIsNull> </div>
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<td class="memname"><a class="el" href="classmysqlpp_1_1Null.html">mysqlpp::Null</a>< Type, Behavior >::<a class="el" href="classmysqlpp_1_1Null.html">Null</a> </td>
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<p>Default constructor. </p>
<p>"data" member is left uninitialized by this ctor, because we don't know what to initialize it to. </p>
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<h2 class="memtitle"><span class="permalink"><a href="#a738398c6aa00bd5a4d691f6277e453ca">◆ </a></span>Null() <span class="overload">[2/3]</span></h2>
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template<class Type, class Behavior = NullIsNull> </div>
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<p>Initialize the object with a particular value. </p>
<p>The object is marked as "not null" if you use this ctor. This behavior exists because the class doesn't encode nulls, but rather data which <em>can</em> <em>be</em> null. The distinction is necessary because 'NULL' is an optional attribute of SQL columns. </p>
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<td class="memname"><a class="el" href="classmysqlpp_1_1Null.html">mysqlpp::Null</a>< Type, Behavior >::<a class="el" href="classmysqlpp_1_1Null.html">Null</a> </td>
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<p>Construct a <a class="el" href="classmysqlpp_1_1Null.html" title="Class for holding data from a SQL column with the NULL attribute.">Null</a> equal to SQL null. </p>
<p>This is typically used with the global <code>null</code> object. (Not to be confused with C's NULL type.) You can say something like... </p><div class="fragment"><div class="line">Null<int> foo = <span class="keyword">null</span>;</div></div><!-- fragment --><p> ...to get a null <code>int</code>. </p>
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<h2 class="groupheader">Member Function Documentation</h2>
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<h2 class="memtitle"><span class="permalink"><a href="#a2ff8415d7070ebbe0462dd78f278d78a">◆ </a></span>operator Type()</h2>
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<p>Converts this object to Type. </p>
<p>If is_null is set, returns whatever we consider that null "is", according to the Behavior parameter you used when instantiating this template. See <a class="el" href="structmysqlpp_1_1NullIsNull.html" title="Class for objects that define SQL null in terms of MySQL++'s null_type.">NullIsNull</a>, <a class="el" href="structmysqlpp_1_1NullIsZero.html" title="Class for objects that define SQL null as 0.">NullIsZero</a> and <a class="el" href="structmysqlpp_1_1NullIsBlank.html" title="Class for objects that define SQL null as a blank C string.">NullIsBlank</a>.</p>
<p>Otherwise, just returns the 'data' member. </p>
<p class="reference">References <a class="el" href="classmysqlpp_1_1Null.html#a11c562b34e0f4f39f34cd36ace40c33e">mysqlpp::Null< Type, Behavior >::data</a>, and <a class="el" href="classmysqlpp_1_1Null.html#a2ce81045c6da00302bb3c998527aab7b">mysqlpp::Null< Type, Behavior >::is_null</a>.</p>
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<p>Do less-than comparison of two nullable values. </p>
<p>Two null objects are equal to each other, and null is less than not-null. If neither is null, we delegate to operator < for the base data type. </p>
<p class="reference">References <a class="el" href="classmysqlpp_1_1Null.html#a11c562b34e0f4f39f34cd36ace40c33e">mysqlpp::Null< Type, Behavior >::data</a>, and <a class="el" href="classmysqlpp_1_1Null.html#a2ce81045c6da00302bb3c998527aab7b">mysqlpp::Null< Type, Behavior >::is_null</a>.</p>
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<p>Do less-than comparison against hard-coded SQL null. </p>
<p>Always returns false because we can only be greater than or equal to a SQL null. </p>
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<p>Assign a value to the object. </p>
<p>This marks the object as "not null" as a side effect. </p>
<p class="reference">References <a class="el" href="classmysqlpp_1_1Null.html#a11c562b34e0f4f39f34cd36ace40c33e">mysqlpp::Null< Type, Behavior >::data</a>, and <a class="el" href="classmysqlpp_1_1Null.html#a2ce81045c6da00302bb3c998527aab7b">mysqlpp::Null< Type, Behavior >::is_null</a>.</p>
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<p>Assign SQL null to this object. </p>
<p>This just sets the is_null flag; the data member is not affected until you call the Type() operator on it. </p>
<p class="reference">References <a class="el" href="classmysqlpp_1_1Null.html#a2ce81045c6da00302bb3c998527aab7b">mysqlpp::Null< Type, Behavior >::is_null</a>.</p>
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<p>Do equality comparison of two nullable values. </p>
<p>Two null objects are equal, and null is not equal to not-null. If neither is null, we delegate to operator == for the base data type. </p>
<p class="reference">References <a class="el" href="classmysqlpp_1_1Null.html#a11c562b34e0f4f39f34cd36ace40c33e">mysqlpp::Null< Type, Behavior >::data</a>, and <a class="el" href="classmysqlpp_1_1Null.html#a2ce81045c6da00302bb3c998527aab7b">mysqlpp::Null< Type, Behavior >::is_null</a>.</p>
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<p>Do equality comparison against hard-coded SQL null. </p>
<p>This tells you the same thing as testing is_null member. </p>
<p class="reference">References <a class="el" href="classmysqlpp_1_1Null.html#a2ce81045c6da00302bb3c998527aab7b">mysqlpp::Null< Type, Behavior >::is_null</a>.</p>
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<h2 class="groupheader">Member Data Documentation</h2>
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<h2 class="memtitle"><span class="permalink"><a href="#a2ce81045c6da00302bb3c998527aab7b">◆ </a></span>is_null</h2>
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<p>If set, this object is considered equal to SQL null. </p>
<p>This flag affects how the Type() and << operators work. </p>
<p class="reference">Referenced by <a class="el" href="classmysqlpp_1_1Null.html#a2ff8415d7070ebbe0462dd78f278d78a">mysqlpp::Null< Type, Behavior >::operator Type()</a>, <a class="el" href="classmysqlpp_1_1Null.html#ae7209f1af6f37a583f914bc616ea64ab">mysqlpp::Null< Type, Behavior >::operator<()</a>, <a class="el" href="classmysqlpp_1_1Null.html#a166ecaa4b711982efe2d8ceee57cd06a">mysqlpp::Null< Type, Behavior >::operator=()</a>, and <a class="el" href="classmysqlpp_1_1Null.html#accd1446f726c245aa894e21a527612d8">mysqlpp::Null< Type, Behavior >::operator==()</a>.</p>
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<hr/>The documentation for this class was generated from the following file:<ul>
<li><a class="el" href="null_8h_source.html">null.h</a></li>
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