In delphi how do I create a string with null separator

Question

I am using SHFileOperation and the source can be a pwidechar with filenames separated by a null and the whole thing terminated with a double null.

I can create an array of widechar and it holds the information I need but when I try to convert to pwidechar for the function, it only copies to the first null.

What am I doing wrong?

David Heffernan · Accepted Answer · 2012-08-29T16:59:53.623

15

Like this:

const
  null = #0;

var
  FileNames: string;
...
FileNames := FileName1 + null + FileName2 + null;

Then pass PWideChar(FileNames) to SHFileOperation.

Because Delphi strings are automatically null-terminated, PWideChar(FileNames) is double null-terminated. One null-terminator that we put on the end, and the automatically added one.

Note that I am assuming that you are using a Unicode Delphi since you talk about wide characters. If you are on an older Delphi, and are calling SHFileOperationW, then declare FileNames to be WideString.

More likely you have a list of files in, say, a string list. Treat them like this:

var
  FileNames: string;
...
if FileList.Count=0 then
  FileNames := null
else
begin
  FileNames := '';
  for i := 0 to FileList.Count-1 do
    FileNames := FileNames + FileList[i] + null;
end;

edited Aug 29 '12 at 16:59

answered Aug 29 '12 at 15:49

David Heffernan

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2

I apologise for the early version of this answer that used '\0', which would have been fine if the language in question was C or C++ !!?! – David Heffernan Aug 29 '12 at 16:08
Oops, you were editing while I was replying. It's all good now :) – Daniel Aug 29 '12 at 16:10
I'm sorry about that @Daniel, I don't know what came over me! – David Heffernan Aug 29 '12 at 16:11
The null-separated string is expected to be double-null-terminated so there should be one final null appended after the loop. – Ondrej Kelle Aug 29 '12 at 16:41
@TOndrej No there should not. Delphi strings are already null terminated, so adding another one would make three in total. – David Heffernan Aug 29 '12 at 16:46
They are terminated with one null, so you need to append another to make it double-null-terminated. Or am I missing something? – Ondrej Kelle Aug 29 '12 at 16:48
Yes you are missing something. Read the text again, the paragraph beginning "because". – David Heffernan Aug 29 '12 at 16:50
@TOndrej On the other hand, my original version did not double null terminate in the case where the list is empty – David Heffernan Aug 29 '12 at 17:00
`null` is not good name for constant (think about `Null` function for variants). – Victoria Sep 12 '17 at 14:38
1

I have this wrapped in a function `function NullDelStr(AStrings: TStrings): String;`. which doesn't use any constant (to avoid confusion @Victoria ) – Jerry Dodge Jan 21 '18 at 21:45

In delphi how do I create a string with null separator

1 Answers1