Wireshark · Ethereal-users: Re: [Ethereal-users] Problem with val_to_str

[Guy Harris <guy@xxxxxxxxxxxx>]

On Wednesday, July 2, 2003, at 2:47 AM, Chua Wee Leng wrote:

> I encounter a proble with val_to_str function while doing my plugin.

That's a developer question, so it should have been sent to 
ethereal-dev@xxxxxxxxxxxx.

> The following is part of my code of protocol dis in packet-dis.c
>
> #define ENTITY_STATE_PDU        	1
> #define FIRE_PDU	        	2
> #define DETONATION_PDU	3
> #define START_RESUME_PDU      13
> #define STOP_FREEZE_PDU         	14
> #define ACKNOWLEDGE_PDU       15
> #define SET_DATA_PDU        	19
> #define DATA_PDU        	20
>
> 	const value_string pdu[] = {
>                                 {ENTITY_STATE_PDU,
> 	"ENTITY_STATE_PDU"},
>                                 {FIRE_PDU,	        	"FIRE_PDU"},
>                                 {DETONATION_PDU,		"DETONATION_PDU"},
>                                 {START_RESUME_PDU,
> 	"START_RESUME_PDU"},
>                                 {STOP_FREEZE_PDU,       
> 	"STOP_FREEZE_PDU"},
>                                 {ACKNOWLEDGE_PDU,       
> 	"ACKNOWLEDGE_PDU"},
> 	        };
>
>         static const value_string vs_Entity_Kind[] = {
>                                 {1,   "Platform"},
>                                 {2,   "Munition"},
>                                 {4,   "Environment"},
>                                 {9,   "Sensor/Emitter"},
> 	      		};

A value_string table *MUST* end with a

	{0, NULL }

item.  Otherwise, the code that converts values to strings will, if 
handed a value not in the table, go past the end of the table.

This is documented in "doc/README.developer":

	strings
	-------
	Some integer fields, of type FT_UINT*, need labels to represent the 
true
	value of a field.  You could think of those fields as having an
	enumerated data type, rather than an integral data type.

	A 'value_string' structure is a way to map values to strings.

	        typedef struct _value_string {
	                guint32  value;
	                gchar   *strptr;
	        } value_string;

	For fields of that type, you would declare an array of "value_string"s:

 	       static const value_string valstringname[] = {
 	               { INTVAL1, "Descriptive String 1" },
 	               { INTVAL2, "Descriptive String 2" },
    	           { 0,       NULL },
        	};

	(the last entry in the array must have a NULL 'strptr' value, to
	indicate the end of the array).  The 'strings' field would be set to
	'VALS(valstringname)'.

Your tables must therefore be

	const value_string pdu[] = {
		{ENTITY_STATE_PDU,		"ENTITY_STATE_PDU"},
		{FIRE_PDU,	        	"FIRE_PDU"},
		{DETONATION_PDU,		"DETONATION_PDU"},
		{START_RESUME_PDU,		"START_RESUME_PDU"},
		{STOP_FREEZE_PDU,		"STOP_FREEZE_PDU"},
		{ACKNOWLEDGE_PDU,		"ACKNOWLEDGE_PDU"},
		{0,						NULL }
	};

	static const value_string vs_Entity_Kind[] = {
		{1,   "Platform"},
		{2,   "Munition"},
		{4,   "Environment"},
		{9,   "Sensor/Emitter"},
		{0,   NULL}
	};