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Update FIELDDESCR with NULL option. 

Example code should never show what not to do.

svn path=/trunk/; revision=23779
This commit is contained in:
Jaap Keuter 2007-12-06 08:02:58 +00:00
parent 7d5edd6075
commit 73a7469bb1
1 changed files with 8 additions and 15 deletions
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doc/README.developer
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@ -1004,7 +1004,7 @@ FIELDBASE BASE_NONE, BASE_DEC, BASE_HEX, BASE_OCT, BASE_DEC_HEX,
BASE_HEX_DEC, BASE_RANGE_STRING
FIELDCONVERT VALS(x), RVALS(x), TFS(x), NULL
BITMASK Usually 0x0 unless using the TFS(x) field conversion.
FIELDDESCR A brief description of the field.
FIELDDESCR A brief description of the field, or NULL.
PARENT_SUBFIELD Lower level protocol field used for lookup, i.e. "tcp.port"
ID_VALUE Lower level protocol field value that identifies this protocol
For example the TCP or UDP port number
@ -2463,10 +2463,10 @@ Example: (from the scsi dissector)
...
{ &hf_scsi_inq_peripheral,
{"Peripheral", "scsi.inquiry.preipheral", FT_UINT8, BASE_HEX,
NULL, 0, "", HFILL}},
NULL, 0, NULL, HFILL}},
{ &hf_scsi_inq_qualifier,
{"Qualifier", "scsi.inquiry.qualifier", FT_UINT8, BASE_HEX,
VALS (scsi_qualifier_val), 0xE0, "", HFILL}},
VALS (scsi_qualifier_val), 0xE0, NULL, HFILL}},
...
Which provides very pretty dissection of this one byte bitmask.
@ -2495,15 +2495,8 @@ table handles all possible values of the size of 'val'", not "the
protocol spec says it has to be" - protocol specs do not prevent invalid
packets from being put onto a network or into a purported packet capture
file), you must check whether 'match_strval()' returns NULL, and arrange
that its return value not be dereferenced if it's NULL. In particular,
don't use it in a call to generate a COL_INFO line for a frame such as
col_add_fstr(COL_INFO, ", %s", match_strval(val, table));
unless is it certain that 'val' is in 'table'.
'val_to_str()' can be used to generate a string for values not found in
the table:
that its return value not be dereferenced if it's NULL. 'val_to_str()'
can be used to generate a string for values not found in the table:
gchar*
val_to_str(guint32 val, const value_string *vs, const char *fmt)
@ -2512,9 +2505,9 @@ If the value 'val' is found in the 'value_string' table pointed to by
'vs', 'val_to_str' will return the corresponding string; otherwise, it
will use 'fmt' as an 'sprintf'-style format, with 'val' as an argument,
to generate a string, and will return a pointer to that string.
(Currently, it has three 64-byte static buffers, and cycles through
them; this permits the results of up to three calls to 'val_to_str' to
be passed as arguments to a routine using those strings.)
You can use it in a call to generate a COL_INFO line for a frame such as
col_add_fstr(COL_INFO, ", %s", val_to_str(val, table, "Unknown %d"));
1.7.2 match_strrval and rval_to_str.