Re: [sqlite] Extra functions - New Project?

[John Stanton]

Mikey, I think that you are on the right track and placing your code in 
the right place.

I probably have the core of many of the functions you want, all coded in 
ANSI C which fits straight into Sqlite.  The conditional compile 
approach would work very well and efficiently, applying no overhead to 
speak of.  As I envisage it you would have a "myfuncs.c" file and a 
conditional compile called say "SQLITE_USER_FUNCS" which if set in the 
makefile would compile in your user functions to a new version of Sqlite.

You would just have to convince Dr Hipp to add the conditional compile 
to the release code.

Mikey C wrote:
I would rather add these functions directly to the core SQLite DLL in C in
and compile them directly into the code (using a conditional).

For example on the web I found an example of adding a sign() function:

/*
** Implementation of the sign() function
*/
static void signFunc(sqlite3_context *context, int argc, sqlite3_value
**argv){
  assert( argc==1 );
  switch( sqlite3_value_type(argv[0]) ){
    case SQLITE_INTEGER: {
      i64 iVal = sqlite3_value_int64(argv[0]);
 /* 1st change below. Line below was:  if( iVal<0 ) iVal = iVal * -1;     */

      iVal = ( iVal > 0) ? 1: ( iVal < 0 ) ? -1: 0;
      sqlite3_result_int64(context, iVal);
      break;
    }
    case SQLITE_NULL: {
      sqlite3_result_null(context);
      break;
    }
    default: {
 /* 2nd change below. Line for abs was: if( rVal<0 ) rVal = rVal * -1.0;  */

      double rVal = sqlite3_value_double(argv[0]);
      rVal = ( rVal > 0) ? 1: ( rVal < 0 ) ? -1: 0;
      sqlite3_result_double(context, rVal);
      break;
    }
  }
}

They then register this function by adding it to the array of existing
functions:

  } aFuncs[] = {
    { "min",               -1, 0, SQLITE_UTF8,    1, minmaxFunc },
    { "min",                0, 0, SQLITE_UTF8,    1, 0          },
    { "max",               -1, 2, SQLITE_UTF8,    1, minmaxFunc },
    { "max",                0, 2, SQLITE_UTF8,    1, 0          },
    { "typeof",             1, 0, SQLITE_UTF8,    0, typeofFunc },
    { "length",             1, 0, SQLITE_UTF8,    0, lengthFunc },
    { "substr",             3, 0, SQLITE_UTF8,    0, substrFunc },
    { "substr",             3, 0, SQLITE_UTF16LE, 0, sqlite3utf16Substr },
    { "abs",                1, 0, SQLITE_UTF8,    0, absFunc    },
    /*  Added here */
    { "sign",               1, 0, SQLITE_UTF8,    0, signFunc   },
    { "round",              1, 0, SQLITE_UTF8,    0, roundFunc  },
    { "round",              2, 0, SQLITE_UTF8,    0, roundFunc  },


This seems to work (I've tried it).

HOWEVER, it means altering func.c and I was looking for how to add these
functions in a separate C file without having to alter any existing code?

Anyone any ideas how best to extend the codebase of SQLite with minimal
alteration to existing code?

Cheers,

Mike

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