String comparison in Delphi - delphi

Question

I have two strings, which I need to compare for equality.
String 1 is created in this way:
var
inBuf: array[0..IN_BUF_SIZE] of WideChar;
stringBuilder : TStringBuilder;
mystring1:string;
...
begin
stringBuilder := TStringBuilder.Create;
for i := startOfInterestingPart to endOfInterestingPart do
begin
stringBuilder.Append(inBuf[i]);
end;
mystring1 := stringBuilder.ToString();
stringBuilder.Free;
String 2 is a constant string 'ABC'.
When string 1 is displayed in a debug console, it is equal to 'ABC'. But the comparisons
AnsiCompareText(mystring1, 'ABC')
mystring1 = 'ABC'
CompareStr(mystring1, 'ABC')
all report inequality.
I suppose that I need to convert string 2 ('ABC') to the same type as the string 1.
How can I do that?
Update 26.09.2012:
aMessage is displayed in the log output as {FDI-MSG-START-Init-FDI-MSG-END}
Here's the code for printing the length of strings:
StringToWideChar('{FDI-MSG-START-Init-FDI-MSG-END}', convString, iNewSize);
...
OutputDebugString(PChar('Len (aMessage): ' + IntToStr(Length(aMessage))));
OutputDebugString(PChar('Len (original constant): ' + IntToStr(Length('{FDI-MSG-START-Init-FDI-MSG-END}'))));
OutputDebugString(PChar('Len (convString): ' + IntToStr(Length(convString))));
And here's the log output:
[3580] Len (aMessage): 40
[3580] Len (original constant): 32
[3580] Len (convString): 0

Answer 1

It looks like you're keeping garbage data in your wide string after the meaningful part, in your update, Length(aMessage) returns 40, while your source string's length is 32.
In Delphi a wide string is COM BSTR compatible, meaning it can hold null characters, a null does not terminate it, it keeps its length at a negative offset of the character data. A possible null character in it helps it to be converted to other string types, but it doesn't alter its own termination.
Consider the below,
const
Source = '{FDI-MSG-START-Init-FDI-MSG-END}';
var
ws: WideString;
size: Integer;
begin
size := 40;
SetLength(ws, size);
StringToWideChar(Source, PWideChar(ws), size);
// the below assertion fails when uncommented
// Assert(CompareStr(Source, ws) = 0);
ws := PWideChar(ws); // or SetLength(ws, Length(Source));
// this assertion does not fail
Assert(CompareStr(Source, ws) = 0);
end;