LacaK via fpc-pascal <fpc-pascal@lists.freepascal.org> schrieb am Di., 1. Dez. 2020, 11:00:
> > Dňa 30.11.2020 o 23:26 Sven Barth via fpc-pascal napísal(a): > > Am 30.11.2020 um 13:20 schrieb LacaK via fpc-pascal: > >> Hi, > >> > >> is there a way how to initialize record member of pointer type (other > >> than PChar) in the following example: > >> > >> type > >> TMyRec=record > >> a: PByte; // if I change PByte to PAnsiChar then it works > >> end; > >> > >> const > >> MyConst: TMyRec = (a: 'abcd'); // I want to a points to static > >> memory where 'abcd' is stored > >> > >> I would like to initialize a to be pointer to another known constant > >> or directly to supplied string constant. > >> > >> For example something like: > >> > >> const > >> MyConst1='abcd'; > >> MyConst2=TMyRec = (a: @MyConst1); > > > > Untyped constants don't have an address you can take. You need to use > > a typed constant: > > > > === code begin === > > > > const > > MyConst1: Byte = 123; > > MyConst2: TMyRec = (a: @MyConst1); > > > > === code end === > > > Thank you, yes it works. I have used: > > const > MyConst1: AnsiString = 'abc' > MyConst2: TMyRec = (a: @MyConst1[1]); > > unfortunately it seems, that I can not use Length(MyConst1) in: > > type > TMyRec=record > l: integer; > a: PByte; > end; > > const > MyConst1: AnsiString = 'abc'; > MyConst2: TMyRec = (l: Length(MyConst1); a: @MyConst1[1]); > > Why is it prohibited? > Because MyConst1 is not an *untyped* constant. Only untyped constants can be used in constant expressions (a pointer to something can be considered an untyped constant). The following might work though I did not test it: === code begin === const MyStr = 'abc' MyConst1: AnsiString = MyStr; MyConst2: TMyRec = (l: Length(MyStr); a: @MyConst1[1]); === code end === Regards, Sven >
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