Language Environment Interface Reference

The dtw_parm_data_t Structure

Net.Data uses the dtw_parm_data_t structure to pass parameters to a language environment. Parameters are obtained from three sources:

• Explicit parameters that are specified on the FUNCTION block definition
• The return variable that is specified on the RETURNS keyword on a FUNCTION block definition
• Parameters that are specified on the ENVIRONMENT configuration statement in the Net.Data initialization file

Net.Data passes explicit parameters first, followed by parameters specified in the ENVIRONMENT statement, and then the return variable.

The dtw_parm_data_t structure has the following format:

typedef struct dtw_parm_data_t {        /* Parameter data             */
    int   parm_descriptor;            /* Parameter descriptor        */
    char *parm_name;                  /* Parameter name              */
    char *parm_value;                 /* Parameter value             */
    void *res1;                       /* Reserved                    */
    void *res2;                       /* Reserved                    */
} dtw_parm_data_t;

Fields in the dtw_parm_data_t structure:

parm_descriptor

The parm_descriptor field describes the type and use of the parameter being passed to the language environment. Net.Data sets the field by performing an OR operation using the following constants:

• DTW_IN indicates that a parameter is an input-only parameter.
• DTW_OUT indicates that a parameter is an output-only parameter.
• DTW_INOUT indicates that a parameter is an input and output parameter.
• DTW_STRING indicates that parameter value is a pointer to a string.
• DTW_TABLE indicates that the parameter value is a pointer to a table.

  Net.Data always sets the parm_descriptor field to DTW_IN, DTW_OUT, or DTW_INOUT and uses a logical OR with DTW_STRING and DTW_TABLE.

parm_name

The parm_name field is a pointer to a string that contains the name of the parameter. Net.Data sets this pointer NULL if the parameter is a literal string.

parm_value

The parm_value field is a pointer to an object that contains the value of the parameter. This pointer is set to NULL by Net.Data if the parameter is a variable that is not already defined.

The res1 and res2 fields are reserved fields.

Both parm_name and parm_value point to an object allocated from the Net.Data run-time heap, the area of memory used for dynamic memory allocation by Net.Data. If parm_name or parm_value is replaced with another string, the original string must be freed and replaced with a pointer to a character string allocated from the Net.Data heap. Use the dtw_malloc() and dtw_free() utility functions to free the original string.