CODEWITHSUNDEEP
delphi
Thomas
Thomas

Reputation: 707

Program freezing on generating random string

I am learning delphi on the german site delphi-treff.

they provide a function to generate random string.

https://www.delphi-treff.de/tipps-tricks/object-pascal/strings/zufallstring-generieren/

function RandomString(strlength: integer): string;
var
  temp : integer;
begin
  randomize;
  repeat
    temp := random(122); //ggf. erhöhen
    if temp in [48..57{0-1}, 65..90{A-Z}, 97..122{a-z}] then
    //Kann um beliebige ASCII-Zeichen erweitert werden,
    //ggf. den Wert in Random hochsetzen
      result := result + Chr(temp);
  until length(result) = strlength;
end;

as you can see here:

if temp in [48..57{0-1}, 65..90{A-Z}, 97..122{a-z}] then

they only put 0-1, A-Z and a-z as characters.

However I thought my program crashes because of this function.

so I changed: until length(result) = strlength;

to: until length(result) >= strlength;

and indeed it sometimes is > strlength.

Can someone explain why it is bigger?

It shouldn't be bigger because it only adds 1 character at a time?

Upvotes: 1

Views: 178

Answers (1)

LU RD
LU RD

Reputation: 34899

Result is treated as an implicit var parameter and must be initialized before use. See What is the default value of 'Result' in Delphi?.

In this case an uninitialized Result parameter will cause the length overflow.

Another issue, Randomize should only be called once at program start.

Upvotes: 4

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