modernc.org/cc@v1.0.1/v2/testdata/_sqlite/ext/misc/remember.c (about)

     1  /*
     2  ** 2016-08-09
     3  **
     4  ** The author disclaims copyright to this source code.  In place of
     5  ** a legal notice, here is a blessing:
     6  **
     7  **    May you do good and not evil.
     8  **    May you find forgiveness for yourself and forgive others.
     9  **    May you share freely, never taking more than you give.
    10  **
    11  *************************************************************************
    12  **
    13  ** This file demonstrates how to create an SQL function that is a pass-through
    14  ** for integer values (it returns a copy of its argument) but also saves the
    15  ** value that is passed through into a C-language variable.  The address of
    16  ** the C-language variable is supplied as the second argument.
    17  **
    18  ** This allows, for example, a counter to incremented and the original
    19  ** value retrieved, atomically, using a single statement:
    20  **
    21  **    UPDATE counterTab SET cnt=remember(cnt,$PTR)+1 WHERE id=$ID
    22  **
    23  ** Prepare the above statement once.  Then to use it, bind the address
    24  ** of the output variable to $PTR using sqlite3_bind_pointer() with a
    25  ** pointer type of "carray" and bind the id of the counter to $ID and
    26  ** run the prepared statement.
    27  **
    28  ** This implementation of the remember() function uses a "carray"
    29  ** pointer so that it can share pointers with the carray() extension.
    30  **
    31  ** One can imagine doing similar things with floating-point values and
    32  ** strings, but this demonstration extension will stick to using just
    33  ** integers.
    34  */
    35  #include "sqlite3ext.h"
    36  SQLITE_EXTENSION_INIT1
    37  #include <assert.h>
    38  
    39  /*
    40  **      remember(V,PTR)
    41  **
    42  ** Return the integer value V.  Also save the value of V in a
    43  ** C-language variable whose address is PTR.
    44  */
    45  static void rememberFunc(
    46    sqlite3_context *pCtx,
    47    int argc,
    48    sqlite3_value **argv
    49  ){
    50    sqlite3_int64 v;
    51    sqlite3_int64 *ptr;
    52    assert( argc==2 );
    53    v = sqlite3_value_int64(argv[0]);
    54    ptr = sqlite3_value_pointer(argv[1], "carray");
    55    if( ptr ) *ptr = v;
    56    sqlite3_result_int64(pCtx, v);
    57  }
    58  
    59  #ifdef _WIN32
    60  __declspec(dllexport)
    61  #endif
    62  int sqlite3_remember_init(
    63    sqlite3 *db, 
    64    char **pzErrMsg, 
    65    const sqlite3_api_routines *pApi
    66  ){
    67    int rc = SQLITE_OK;
    68    SQLITE_EXTENSION_INIT2(pApi);
    69    rc = sqlite3_create_function(db, "remember", 2, SQLITE_UTF8, 0,
    70                                 rememberFunc, 0, 0);
    71    return rc;
    72  }