NAME

structs_type_struct — structs types for C structures

LIBRARY

PDEL Library (libpdel, -lpdel)

SYNOPSIS

#include <sys/types.h>
#include <stddef.h>
#include <pdel/structs/structs.h>
#include <pdel/structs/type/struct.h>

STRUCTS_STRUCT_TYPE(struct_name, field_list);

STRUCTS_STRUCT_FIELD(struct_name, field_name, field_type);

STRUCTS_STRUCT_FIELD2(struct_name, field_name, display_name, field_type);

DESCRIPTION

The STRUCTS_STRUCT_TYPE() macro defines a structs(3) type (i.e., a struct structs_type) for describing the C structure struct struct_name. The field_list parameter must point to an array of struct structs_field structures describing the fields:

/* This structure describes one field in a structure */
struct structs_field {
    const char                  *name;      /* field name */
    const struct structs_type   *type;      /* field type */
    u_int16_t                   size;       /* field size */
    u_int16_t                   offset;     /* field offset */
};

The fields need not be listed in the array in the same order as they are declared in the C structure. However, the array must be terminated with STRUCTS_STRUCT_FIELD_END, which is defined as follows:

#define STRUCTS_STRUCT_FIELD_END {
  NULL, NULL, 0, 0 }

The STRUCTS_STRUCT_FIELD() macro should be used to define an entry in the field array: field_name is the name of the field and field_type is a pointer to the structs(3) type describing the field.

To define a field and give it a different structs(3) name than its name in the C structure, use STRUCTS_STRUCT_FIELD2() with the desired display_name in double quotes.

EXAMPLES

The program below prints out the contents (as an ASCII string) of the field specified on the command line:

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <stdio.h>
#include <stdlib.h>
#include <err.h>

#include <pdel/structs/structs.h>
#include <pdel/structs/type/struct.h>
#include <pdel/structs/type/string.h>
#include <pdel/structs/type/ip4.h>
#include <pdel/util/typed_mem.h>

/* My structure */
struct foobar {
        char            *name;
        u_int16_t       index;
        struct in_addr  ipaddr;
};

/* Structs type describing a 'struct foobar' */
static const struct structs_field foobar_fields = {
        STRUCTS_STRUCT_FIELD(foobar, name, &structs_type_string),
        STRUCTS_STRUCT_FIELD(foobar, index, &structs_type_uint16),
        STRUCTS_STRUCT_FIELD(foobar, ipaddr, &structs_type_ip4),
        STRUCTS_STRUCT_FIELD_END
};
static const struct structs_type foobar_type =
        STRUCTS_STRUCT_TYPE(foobar, &foobar_fields);

int
main(int argc, char **argv)
{
	struct foobar f;
	const char *fieldname;
	char *fieldvalue;

	/* Initialize our structure with some contents */
	if (structs_init(&foobar_type, NULL, &f) == -1)
		err(1, "structs_init");
	f.index = 123;
	(void)inet_aton("12.34.56.78", &f.ipaddr);
	if (structs_set_string(&foobar_type, "name",
	    "this is a string", &f, NULL, 0) == -1)
		err(1, "structs_set_string");

	/* Get the requested field's name from the command line */
	if (argc != 2)
		err(1, "usage: getfield <fieldname>");
	fieldname = argv[1];

	/* Display the requested field's value */
	if ((fieldvalue = structs_get_string(&foobar_type,
	    fieldname, &f, TYPED_MEM_TEMP)) == NULL)
		err(1, "%s", fieldname);
	printf("The value of field \"%s\" is: %s\n",
	    fieldname, fieldvalue);

	/* Done, clean up */
	FREE(TYPED_MEM_TEMP, fieldvalue);
	structs_free(&foobar_type, NULL, &f);
	return (0);
}

HISTORY

The PDEL library was developed at Packet Design, LLC. http://www.packetdesign.com/

AUTHORS

Archie Cobbs ⟨archie@freebsd.org⟩