204 lines
7.8 KiB
HTML
204 lines
7.8 KiB
HTML
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<!-- keywords: sqlite3_create_collation sqlite3_create_collation16 sqlite3_create_collation_v2 -->
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<a href="intro.html"><h2>SQLite C Interface</h2></a>
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<h2>Define New Collating Sequences</h2>
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</div>
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<blockquote><pre>
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int sqlite3_create_collation(
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sqlite3*,
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const char *zName,
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int eTextRep,
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void *pArg,
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int(*xCompare)(void*,int,const void*,int,const void*)
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);
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int sqlite3_create_collation_v2(
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sqlite3*,
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const char *zName,
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int eTextRep,
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void *pArg,
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int(*xCompare)(void*,int,const void*,int,const void*),
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void(*xDestroy)(void*)
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);
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int sqlite3_create_collation16(
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sqlite3*,
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const void *zName,
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int eTextRep,
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void *pArg,
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int(*xCompare)(void*,int,const void*,int,const void*)
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);
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</pre></blockquote>
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<p>
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These functions add, remove, or modify a <a href="../datatype3.html#collation">collation</a> associated
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with the <a href="../c3ref/sqlite3.html">database connection</a> specified as the first argument.</p>
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<p>The name of the collation is a UTF-8 string
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for sqlite3_create_collation() and sqlite3_create_collation_v2()
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and a UTF-16 string in native byte order for sqlite3_create_collation16().
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Collation names that compare equal according to <a href="../c3ref/stricmp.html">sqlite3_strnicmp()</a> are
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considered to be the same name.</p>
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<p>The third argument (eTextRep) must be one of the constants:
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<ul>
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<li> <a href="../c3ref/c_any.html">SQLITE_UTF8</a>,
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<li> <a href="../c3ref/c_any.html">SQLITE_UTF16LE</a>,
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<li> <a href="../c3ref/c_any.html">SQLITE_UTF16BE</a>,
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<li> <a href="../c3ref/c_any.html">SQLITE_UTF16</a>, or
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<li> <a href="../c3ref/c_any.html">SQLITE_UTF16_ALIGNED</a>.
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</ul>
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The eTextRep argument determines the encoding of strings passed
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to the collating function callback, xCompare.
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The <a href="../c3ref/c_any.html">SQLITE_UTF16</a> and <a href="../c3ref/c_any.html">SQLITE_UTF16_ALIGNED</a> values for eTextRep
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force strings to be UTF16 with native byte order.
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The <a href="../c3ref/c_any.html">SQLITE_UTF16_ALIGNED</a> value for eTextRep forces strings to begin
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on an even byte address.</p>
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<p>The fourth argument, pArg, is an application data pointer that is passed
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through as the first argument to the collating function callback.</p>
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<p>The fifth argument, xCompare, is a pointer to the collating function.
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Multiple collating functions can be registered using the same name but
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with different eTextRep parameters and SQLite will use whichever
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function requires the least amount of data transformation.
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If the xCompare argument is NULL then the collating function is
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deleted. When all collating functions having the same name are deleted,
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that collation is no longer usable.</p>
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<p>The collating function callback is invoked with a copy of the pArg
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application data pointer and with two strings in the encoding specified
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by the eTextRep argument. The two integer parameters to the collating
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function callback are the length of the two strings, in bytes. The collating
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function must return an integer that is negative, zero, or positive
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if the first string is less than, equal to, or greater than the second,
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respectively. A collating function must always return the same answer
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given the same inputs. If two or more collating functions are registered
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to the same collation name (using different eTextRep values) then all
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must give an equivalent answer when invoked with equivalent strings.
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The collating function must obey the following properties for all
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strings A, B, and C:</p>
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<p><ol>
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<li> If A==B then B==A.
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<li> If A==B and B==C then A==C.
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<li> If A<B THEN B>A.
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<li> If A<B and B<C then A<C.
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</ol></p>
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<p>If a collating function fails any of the above constraints and that
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collating function is registered and used, then the behavior of SQLite
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is undefined.</p>
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<p>The sqlite3_create_collation_v2() works like sqlite3_create_collation()
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with the addition that the xDestroy callback is invoked on pArg when
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the collating function is deleted.
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Collating functions are deleted when they are overridden by later
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calls to the collation creation functions or when the
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<a href="../c3ref/sqlite3.html">database connection</a> is closed using <a href="../c3ref/close.html">sqlite3_close()</a>.</p>
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<p>The xDestroy callback is <u>not</u> called if the
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sqlite3_create_collation_v2() function fails. Applications that invoke
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sqlite3_create_collation_v2() with a non-NULL xDestroy argument should
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check the return code and dispose of the application data pointer
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themselves rather than expecting SQLite to deal with it for them.
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This is different from every other SQLite interface. The inconsistency
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is unfortunate but cannot be changed without breaking backwards
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compatibility.</p>
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<p>See also: <a href="../c3ref/collation_needed.html">sqlite3_collation_needed()</a> and <a href="../c3ref/collation_needed.html">sqlite3_collation_needed16()</a>.
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</p><p>See also lists of
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<a href="objlist.html">Objects</a>,
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<a href="constlist.html">Constants</a>, and
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<a href="funclist.html">Functions</a>.</p>
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