gawk: Two-way processors
16.4.5.6 Customized Two-way Processors
......................................
A "two-way processor" combines an input parser and an output wrapper for
two-way I/O with the '|&' operator (
Redirection). It makes
identical use of the 'awk_input_parser_t' and 'awk_output_buf_t'
structures as described earlier.
A two-way processor is represented by the following structure:
typedef struct awk_two_way_processor {
const char *name; /* name of the two-way processor */
awk_bool_t (*can_take_two_way)(const char *name);
awk_bool_t (*take_control_of)(const char *name,
awk_input_buf_t *inbuf,
awk_output_buf_t *outbuf);
awk_const struct awk_two_way_processor *awk_const next; /* for gawk */
} awk_two_way_processor_t;
The fields are as follows:
'const char *name;'
The name of the two-way processor.
'awk_bool_t (*can_take_two_way)(const char *name);'
The function pointed to by this field should return true if it
wants to take over two-way I/O for this file name. It should not
change any state (variable values, etc.) within 'gawk'.
'awk_bool_t (*take_control_of)(const char *name,'
' awk_input_buf_t *inbuf,'
' awk_output_buf_t *outbuf);'
The function pointed to by this field should fill in the
'awk_input_buf_t' and 'awk_output_buf_t' structures pointed to by
'inbuf' and 'outbuf', respectively. These structures were
described earlier.
'awk_const struct two_way_processor *awk_const next;'
This is for use by 'gawk'; therefore it is marked 'awk_const' so
that the extension cannot modify it.
As with the input parser and output processor, you provide "yes I can
take this" and "take over for this" functions, 'XXX_can_take_two_way()'
and 'XXX_take_control_of()'.
You register your two-way processor with the following function:
'void register_two_way_processor(awk_two_way_processor_t *two_way_processor);'
Register the two-way processor pointed to by 'two_way_processor'
with 'gawk'.
Info Catalog
gawk: Output Wrappers
gawk: Registration Functions