How to use reserved members of a struct

Carnildo

From header1.h

typedef struct {

	// Large number of fields snipped

	short				reserved1;			// Used by DSI
	long				reserved2;			// Ditto -- fence data
	double				reserved3;			// Ditto -- RESERVED Value
	short				reserved4;			// Ditto -- max alt refs built
	short				reserved5;			// Ditto -- number of sig digits
	long				reserved6;			// mine

	// More fields snipped

} subrec, *subptr;

From header2.h:

typedef struct {

	// Large number of fields snipped

	short		reserved1;		// Used by DSI
	long		reserved2;		// Ditto -- fence data
	double		reserved3;		// Ditto -- RESERVED Value
	short		reserved4;		// Ditto -- max alt refs built
	short		reserved5;		// Ditto -- number of sig digits
	long		reserved6;		// mine
} OBJECTSTRUCT;

From header3.h

// redefinition of the OBJECTSTRUCT reserve fields so they are more user friendly

#define type_id			reserved1
#define plus_fence_ref		reserved2
#define value			reserved3
#define max_alt_num		reserved4
#define sig_digits		reserved5
#define rows_columns		reserved6

The names and types of the six "reserved" fields are the only things that the two structs have in common.

Mole

Using a compiler that doesn't support unions, so they use reserved structure members instead and then #define them?

Still, I can think of several situations where #define'ing reservedX can cause some subtle bugs that could take hours to track down... So its still a WTF,

Heron

@Mole said:

Using a compiler that doesn't support unions, so they use reserved structure members instead and then #define them?

I don't see what unions have to do with anything...

Mole

As in, I've seen this kind of thing before:

typedef struct { // common record structure

	// Large number of fields snipped

	short				reserved1;			// Used by DSI
	long				reserved2;			// Ditto -- fence data
	double				reserved3;			// Ditto -- RESERVED Value
	short				reserved4;			// Ditto -- max alt refs built
	short				reserved5;			// Ditto -- number of sig digits
	long				reserved6;			// mine

	// More fields snipped

} subrec, *subptr;

// redefinition of structure as 'rectype'

#define type_id			reserved1
#define plus_fence_ref		reserved2
#define value			reserved3
#define max_alt_num		reserved4
#define sig_digits		reserved5
#define rows_columns		reserved6

// redefinition of structure as 'rectype2'

#define type_id			reserved1
#define foo_ref			reserved2

etc... so the same structure can handle many different formats. You can read from a file into a structure and then reference depending on the type_id of the first field.