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73 lines
2.2 KiB
C
73 lines
2.2 KiB
C
/*
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** 2016-08-09
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**
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** The author disclaims copyright to this source code. In place of
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** a legal notice, here is a blessing:
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**
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** May you do good and not evil.
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** May you find forgiveness for yourself and forgive others.
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** May you share freely, never taking more than you give.
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**
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*************************************************************************
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**
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** This file demonstrates how to create an SQL function that is a pass-through
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** for integer values (it returns a copy of its argument) but also saves the
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** value that is passed through into a C-language variable. The address of
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** the C-language variable is supplied as the second argument.
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**
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** This allows, for example, a counter to incremented and the original
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** value retrieved, atomically, using a single statement:
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**
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** UPDATE counterTab SET cnt=remember(cnt,$PTR)+1 WHERE id=$ID
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**
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** Prepare the above statement once. Then to use it, bind the address
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** of the output variable to $PTR using sqlite3_bind_pointer() with a
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** pointer type of "carray" and bind the id of the counter to $ID and
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** run the prepared statement.
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**
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** This implementation of the remember() function uses a "carray"
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** pointer so that it can share pointers with the carray() extension.
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**
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** One can imagine doing similar things with floating-point values and
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** strings, but this demonstration extension will stick to using just
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** integers.
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*/
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#include "sqlite3ext.h"
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SQLITE_EXTENSION_INIT1
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#include <assert.h>
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/*
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** remember(V,PTR)
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**
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** Return the integer value V. Also save the value of V in a
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** C-language variable whose address is PTR.
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*/
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static void rememberFunc(
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sqlite3_context *pCtx,
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int argc,
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sqlite3_value **argv
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){
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sqlite3_int64 v;
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sqlite3_int64 *ptr;
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assert( argc==2 );
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v = sqlite3_value_int64(argv[0]);
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ptr = sqlite3_value_pointer(argv[1], "carray");
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if( ptr ) *ptr = v;
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sqlite3_result_int64(pCtx, v);
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}
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#ifdef _WIN32
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__declspec(dllexport)
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#endif
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int sqlite3_remember_init(
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sqlite3 *db,
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char **pzErrMsg,
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const sqlite3_api_routines *pApi
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){
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int rc = SQLITE_OK;
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SQLITE_EXTENSION_INIT2(pApi);
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rc = sqlite3_create_function(db, "remember", 2, SQLITE_UTF8, 0,
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rememberFunc, 0, 0);
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return rc;
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}
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