-
unsigned int arg_count
The number of arguments. Check this value in the
initialization function if you require your function to be
called with a particular number of arguments. For example:
if (args->arg_count != 2)
{
strcpy(message,"XXX() requires two arguments");
return 1;
}
-
enum Item_result *arg_type
A pointer to an array containing the types for each
argument. The possible type values are
STRING_RESULT,
INT_RESULT, and
REAL_RESULT.
To make sure that arguments are of a given type and return
an error if they are not, check the
arg_type array in the initialization
function. For example:
if (args->arg_type[0] != STRING_RESULT ||
args->arg_type[1] != INT_RESULT)
{
strcpy(message,"XXX() requires a string and an integer");
return 1;
}
As an alternative to requiring your function's arguments
to be of particular types, you can use the initialization
function to set the arg_type elements
to the types you want. This causes MySQL to coerce
arguments to those types for each call to
xxx(). For example, to specify that the
first two arguments should be coerced to string and
integer, respectively, do this in
xxx_init():
args->arg_type[0] = STRING_RESULT;
args->arg_type[1] = INT_RESULT;
-
char **args
args->args communicates information
to the initialization function about the general nature of
the arguments passed to your function. For a constant
argument i,
args->args[i] points to the argument
value. (See below for instructions on how to access the
value properly.) For a non-constant argument,
args->args[i] is
0. A constant argument is an expression
that uses only constants, such as 3 or
4*7-2 or SIN(3.14).
A non-constant argument is an expression that refers to
values that may change from row to row, such as column
names or functions that are called with non-constant
arguments.
For each invocation of the main function,
args->args contains the actual
arguments that are passed for the row currently being
processed.
Functions can refer to an argument i as
follows:
An argument of type STRING_RESULT
is given as a string pointer plus a length, to allow
handling of binary data or data of arbitrary length.
The string contents are available as
args->args[i] and the string
length is args->lengths[i]. You
should not assume that strings are null-terminated.
-
For an argument of type INT_RESULT,
you must cast args->args[i] to a
long long value:
long long int_val;
int_val = *((long long*) args->args[i]);
-
For an argument of type
REAL_RESULT, you must cast
args->args[i] to a
double value:
double real_val;
real_val = *((double*) args->args[i]);
-
unsigned long *lengths
For the initialization function, the
lengths array indicates the maximum
string length for each argument. You should not change
these. For each invocation of the main function,
lengths contains the actual lengths of
any string arguments that are passed for the row currently
being processed. For arguments of types
INT_RESULT or
REAL_RESULT, lengths
still contains the maximum length of the argument (as for
the initialization function).
