On 03.07.2018 19:00, Ralf Quint wrote:
On 7/3/2018 9:40 AM, Ondrej Pokorny wrote:
1.) SetLength itself produces an unitialized block of data within the
variable if the new length is bigger than the old length.
Therefore it would be more appropriate to get an "uninitialized
warning" after SetLength:
program Project1;
var
S: string;
begin
SetLength(S, 10); // <<< warning here --->> WHY ????
Writeln(S[2]); // <<< no warning here --->> WHY ????
end.
The program does EXACTLY what you told it to do and the compiler gives
you an explicit warning that that what you are doing is potentially
wrong/dangerous.
No no no. You miss the point and you are wrong.
The compiler tells me that the line "SetLength(S, 10);" is potentially
dangerous, which it is not.
The line "Writeln(S[2]);" is potentially dangerous, but the compiler
does not warn me about it.
=> The compiler warns me about the wrong line.
See:
program Project1;
var
S: string[10];
begin
Writeln(S[2]); // <<< warning here --->> OK
end.
With your arguments I should get a warning while at line "S:
string[10];" and no warning at "Writeln(S[2]);". Seriously?
If you set the length of a string, without it having been
initialized/assigned a value, all you do is to tell the program that you
have now a string of a specified length. And as long as you do not
exceed that specified length, there is no reason for the compiler to
complain about it. YOU explicitly defined that accessing any
character/element up to that defined length is valid!
You as a programmer failed to heed the warning at the SetLength()
function and adjusted your code accordingly. You as a programmer should
realize that there are random characters in the string if you extend the
length of the string. How is the extended length to be initialized?
Blanks (0x20), Zeroes (0x00)?
You obviously miss my point. Please read my previous email again. I
don't feel the need to go into this discussion because it is off-topic.
What about the following example?
Program ABC;
Var S : String;
begin
S := '12345';
SetLength (S, 10);
WriteLn (S [2]);
WriteLn (S [7]);
end.
I should get a warning in line "WriteLn (S [2]);". (Btw. if you read my
previous email carefully you would see that this case is covered in
point 5.)
The same as I get a warning in (the same example as above):
program Project1;
var
S: string[10];
begin
Writeln(S[2]); // <<< warning here --->> OK
end.
Ondrej
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