Why Doesn't Delphi 2009 Give A Message For A String Constant that is Too Long?

Question

It got me stuck for an hour. I happened to have a string constant with about 280 characters in it.

I was trying to use Pos to look for a substring within a long string constant. It gives the result 0 when the string is longer than 255 characters, but gives the correct result when the string is shorter.

e.g.:

pos('5', '123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.12345')

Containing 255 characters correctly returns the number 5.

pos('5', '123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456')

Containing 256 characters gives a compiler error: [DCC Error] E2056 String literals may have at most 255 elements.

pos('5', '123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.1234567')

But 257 characters or more does not produce any messages and incorrectly returns the number 0.

This led me on a wild goose chase for a while.

I also found the same is true for a simple assignment to a string, e.g.:

S1 :='123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456789.123456';

gives that error message and won't compile.

But add one more character, and S1 is assigned a null string.

Is there a Delphi option that should be turned on to warn me of this, or is this just a "bug" by the Embarcadero programmers?

Could someone please check if Delphi 2010 now gives a message for all strings >= 255 characters, or for just 256 characters and not for those >= 257.

If not, how do I go about getting it noticed at Quality Central? I can't even figure out how to see if that problem has been reported.

---

Thanks for allowing me to vent.

Kornel's answer linked to a forum discussion that links to the bug report that says it has been fixed in build 14.0.3513.24210.

---

p.s. Don't you think Embarcadero should have eliminated the 255 limit when Delphi 2009's Unicode strings were introduced?

Answer 1

Are you using AnsiStrings or ShortStrings? ShortStrings (string) have a cap on length, AnsiStrings don't (they're null terminated). Or alternatively, have you tried compiling with {$H+} (AnsiStrings by default)?

To get over the length limit of the constant, use "split longer into addition" + "of shorter strings under 255 chars".

Also, there's a similar discussion on the Delphi support forums here.

I assume that the reason why the literals can't be longer is because the compiler stores them as short strings (not to allocate them on heap) hence the one-byte-size length limit stands here.

As for why Delphi doesn't report it... well, it's a known bug that supposedly has been fixed, and even has a compiler patch.

Answer 2

Delphi has a limit of 255 characters for a string constant. You can make it longer I think by concatinating together using + but its a very old limit based on the fact that in pascal and Delphi 1 all Strings were limited to a maximum of 255 characters.

Annoying but easily worked around.