Just an example of how to do the casting when working with integer values. Only one function, square(), which squares a given value. eg: SELECT square(2) -> 4

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/*
   Copyright ?1998 by Nem W Schlecht
   This file is public domain and comes with NO WARRANTY of any kind

MySQL SQL code for creating/deleting this function in the 'mysql' database:

CREATE FUNCTION square RETURNS INTEGER SONAME "int_example.so";
DROP FUNCTION square;

Compile line:

CC -DMYSQL_SERVER -DDEFAULT_MYSQL_HOME="\"/local/mysql\""
-DDATADIR="\"/local/mysql/var\"" -DSHAREDIR="\"/local/mysql/share/mysql\""
-DHAVE_CONFIG_H -DUSE_ALARM_THREAD -O3 -DDBUG_OFF
-I/local/mysql/include/mysql -I/local/src/SQL/mysql-3.22.4-beta/include
-I/local/src/SQL/mysql-3.22.4-beta -shared -o int_example.so int_example.cc

*/

#include <global.h>
#include <my_sys.h>
#include <mysql.h>
#include <m_ctype.h>

#ifdef HAVE_DLOPEN

extern "C" {

// The initialization function proto.
my_bool square_init(UDF_INIT *initid, UDF_ARGS *args, char *message);

// The de-initialzition function proto.
void square_deinit(UDF_INIT *initid);

// The actual function proto.
longlong square(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error);
}

//
// Initialization function - make sure correct number of arguments are passed
// and that the argument is an integer value
my_bool square_init(UDF_INIT *initid, UDF_ARGS *args, char *message)
{
  if (args->arg_count != 1 || args->arg_type[0] != INT_RESULT) {
    strcpy(message,"Wrong arguments to square");
    return 1;
  }

  initid->maybe_null = 0;
  return 0;
}

//
// De-initialization function - nothing spectial
void square_deinit(UDF_INIT *initid)
{
}

//
// 'square' function.  Returns the square of the integer passed to it in the
// args structure
long long square(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error)
{
    int number = *((long long*) args->args[0]);
    return number*number;
}

#endif /* HAVE_DLOPEN */