External function prototypes

This section describes the API for functions in external libraries.

The API is defined by a header file named extfnapi.h, in the h subdirectory of your Sybase IQ installation directory. This header file handles the platform-dependent features of external function prototypes.

To notify the database server that the library is not written using the old API, you must provide a function as follows:

uint32 extfn_use_new_api( )

The function returns an unsigned 32-bit integer. If the return value is non-zero, the database server assumes that you are not using the old API.

If the function is not exported by the DLL, the database server assumes that the old API is in use. When using the new API, the returned value must be the API version number defined in extfnapi.h.

The name of the function must match that referenced in the CREATE PROCEDURE or CREATE FUNCTION statement. The function declaration must be as follows:

void function-name ( an_extfn_api *api, void *argument-handle )

The function must return void, and must take as arguments a structure used to pass the arguments, and a handle to the arguments provided by the SQL procedure.

The an_extfn_api structure has the following form:

typedef struct an_extfn_api {
    short (SQL_CALLBACK *get_value)(
				    void *          arg_handle,
				    a_sql_uint32    arg_num,
				    an_extfn_value *value
				    );
    short (SQL_CALLBACK *get_piece)(
				    void *          arg_handle,
				    a_sql_uint32    arg_num,
				    an_extfn_value *value,
				    a_sql_uint32    offset
				    );
    short (SQL_CALLBACK *set_value)(
				    void *          arg_handle,
				    a_sql_uint32    arg_num,
				    an_extfn_value *value
				    short          append
				    );
void (SQL_CALLBACK *set_cancel)(
				    void *	arg_handle,
				    void *	cancel_handle
				    );
} an_extfn_api;

The an_extfn_value structure has the following form:

typedef struct an_extfn_value {
    void *				data;
    a_sql_uint32 		piece_len;
    union {
        a_sql_uint32	total_len; 
        a_sql_uint32	remain_len; 
    } len;
    a_sql_data_type		type;
} an_extfn_value;

Calling get_value on an OUT parameter returns the data type of the argument, and returns data as NULL.

The get_piece function for any given argument can only be called immediately after the get_value function for the same argument,

To return NULL, set data to NULL in an_extfn_value.

The append field of set_value determines whether the supplied data replaces (false) or appends to (true) the existing data. You must call set_value with append=FALSE before calling it with append=TRUE for the same argument. The append field is ignored for fixed length data types.

The header file itself contains some additional notes.

An external function that expects to be canceled must inform the database server by calling the set_cancel API function. You must export a special function to enable external operations to be canceled. This function must have the following form:

void an_extfn_cancel ( void * cancel_handle )

If the DLL does not export this function, the database server ignores any user interrupts for functions in the DLL. In this function, cancel_handle is a pointer provided by the function being cancelled to the database server upon each call to the external function by the set_cancel API function listed in the an_extfn_api structure, above.