On 23/02/2025 20:42, Martin Frb wrote:
function Foo: ansistring;
var s: ansistring;
begin
SetLenght(s, 10000); fillchar(@s[1], 10000, ' ');
SetLenght(Result, 10000); fillchar(@Result[1], 10000, ' ');
end;
...
So in the original example above, if either string is having a large
content (pointing to a length = 1MB chars area), then SetLengh would
copy "10000" chars of that into the new unique string.
Such a copy would be an unnecessary cost.
I know this will happen (with smaller length) when using -gt.
But will it ever happen in any other case?
So yes I found an example for result. The length of result will have the
previous value.
program Project1; {$Mode objfpc}
function bar: AnsiString;
begin
writeln(Length(Result));
SetLength(Result, random(20));
end;
procedure foo;
var a: String;
begin
repeat a := bar; until a = '';
end;
begin
foo; readln;
end.
Leaves the question: What about local vars?
-------------------
As a side note
program Project1;
procedure foo;
var
s: ansistring;
begin
SetLength(s, 100);
end;
begin
foo;
end.
Compile with -O3 and somehow the compiler realizes that s is
initialized. The warning is gone.
Interestingly -O3 will also do that for "result" in "function foo:
ansistring;" => Doesn't that depend on the caller, or is there some
magic?
Any idea why -O3 does not print the warning?
In my new example "result" will be having the previous value, even with
O3. So it should be giving that warning?
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