How to decode and display as ASCII?

I had tried that...when I used field types FT_STRING and FT_STRINGZ, nothing is displayed, and when I use FT_UNIT_STRING, I get an error saying: [Dissector bug, protocol PFCP: proto.c:1115: failed assertion "DISSECTOR_ASSERT_NOT_REACHED"]

I'm not sure if I possibly did something wrong. Here is my code dealing with this.

{ &hf_pfcp_ipAddressStr, { "PFCP IP Address String", "pfcp.ipAddressStr", FT_UINT_STRING, BASE_NONE, NULL, 0, NULL, HFILL } },

proto_tree_add_item(pfcp_tree, hf_pfcp_ipAddressStr, tvb, offset, 15, ENC_ASCII); offset += 15;

OK, this is a bit confusing. FT_UINT_STRING is for "counted" strings, where the string has an integral count of characters, followed by the characters. The length you specify is the length in proto_tree_add_item() is the length of the count in bytes, and it has to be between 1 and 4 bytes. In addition, you have to specify the byte-order of the count (ENC_ASCII|ENC_BIG_ENDIAN or ENC_ASCII|ENC_LITTLE_ENDIAN), and to do the offset += N; you'd have to fetch the count yourself and add it to the offset.

So what format is the string in?

I'm sorry I'm new to all of this, what do you mean by "what format is the string in"? And I believe the field type I'm going to be wanting to use is FT_STRING, if that makes any difference.

Is it:

• 15 bytes of ASCII characters, and always 15 bytes long?

• 0 to 15 bytes of ASCII characters, padded at the end with NULs (bytes with a value of 0);

• an arbitrary number of ASCII characters, with a NUL at the end (so that it's not always 15 bytes long);

• a 1-to-4-byte count of characters, followed by that number of ASCII characters (so that it's not always 15 bytes long);

• something else?

Its 15 bytes of ASCII, always being 15 bytes. Its supposed to represent an IP address in the 000.000.000.000 format, each byte representing a digit or a period, always making it 15 bytes.