Mega Code Archive
Determining the actual length of a DBCS string
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Title: Determining the actual length of a DBCS string
Question: How can I get the length in characters of a multibyte-character string? Function Length returns the length in bytes, but in Eastern languages some characters may take more than one byte...
Answer:
Introduction
------------
The Length function returns the length of a string, but it behaves
differently according to the type of the string. For the old short
strings (ShortString) and for long strings (AnsiString), Length
returns the number of bytes they take, while for wide (Unicode)
strings (WideString) it returns the number of wide characters
(WideChar), that is, the number of bytes divided by two. In the
case of short and long strings, in Western languages one character
takes one byte, while for example in Asian languages some characters
take one and others two bytes. For this reason, there are two versions
of almost all string functions, one of great performance that only
works with single-byte character strings (SBCS) and another -less
performant- one that also works with strings where a character can
take one or two bytes (DBCS) that are used in applications distributed
internationally. This way we have functions like Pos, LowerCase and
UpperCase on one side and AnsiPos, AnsiLowerCase and AnsiUpperCase on
the other. Curiosly there is no AnsiLength function that returns the
number of characters in a DBCS.
AnsiLength (Draft)
------------------
Then here it goes a function that returns the number of characters in
a double-byte character string:
function AnsiLength(const s: string): integer;
var
i, n: integer;
begin
Result := 0;
n := Length(s);
i := 1;
while i inc(Result);
if s[i] in LeadBytes then inc(i);
inc(i);
end;
end;
AnsiLength (Final)
------------------
Naturally, this function is not optimized. We are not going to mess
with assembler, but at least we can use pointers:
function AnsiLength(const s: string): integer;
var
p, q: pchar;
begin
Result := 0;
p := PChar(s);
q := p + Length(s);
while p inc(Result);
if p^ in LeadBytes then
inc(p, 2)
else
inc(p);
end;
end;
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