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Frequently Asked Questions

Porting strings from 16 to 32-bit

Question:

When I port my code from 16 to 32 bit, record types that contain strings do not function correctly. What has happened?

Answer:

Traditionally, strings that are defined with no length parameter

would default to having a length of 255 characters. With the advent

of 32 bit Delphi, strings with no defined length default to a long

string. Long strings are pointers to a reference counted AnsiString.

Long string types are not recommended for use in structures that are

intended to be written or read from a disk file. To port your code

correctly, you need to explicitly set the expected length of the

string in the record, otherwise, a long string is used in place of 

the original string in the record, leading to unexpected results.



Example:



  ShortStringRec : record

    s : string[255]; {this uses a short string - ok}

  end;



  LongStringRec : record

    s : string; {this uses a long string - not ok}

  end;

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