Translate unsigned char *buf=NULL to Pascal?

Question

I'm working in Borland Delphi, and i have a few lines code in Borland C++ Builder. I would like to translate these lines into Delphi source.

unsigned char *buf=NULL;
buf=new unsigned char[SPS*2];
for (i=0; i<SPS*2; i++)
   buf[i]=2;

... ....

answers=buf[2];

I would like to assign a PCHar value with this buf;

a:PCHar;
a:=buf.

1) `unsigned char` = `Byte`, not `Char` (blame Ritchie for that), 2) `new` can be translated to `GetMem()` or with intermediate type which declares size 3) for loop is straightforward — Premature Optimization, Nov 01 '11 at 13:42

score 6 · Answer 1 · edited Nov 01 '11 at 13:52

In fact, in:

unsigned char *buf=NULL;
buf=new unsigned char[SPS*2];

The first assignment *buf=NULL can be translated as buf := nil but it is pure dead code, since buf pointer content is immediately overwritten by the new function.

So your C code may be translated as such:

var buf: PAnsiChar;
    i: integer;
begin
  Getmem(buf,SPS*2);
  for i := 0 to SPS*2-1 do
    buf[i] := #2;
...
  Freemem(buf);
end;

A more Delphi-idiomatic version may be:

var buf: array of AnsiChar;
    i: integer;
begin
  SetLength(buf,SPS*2);
  for i := 0 to high(buf) do
    buf[i] := #2;
  ...
  // no need to free buf[] memory (it is done by the compiler)
end;

or directly:

var buf: array of AnsiChar;
    i: integer;
begin
  SetLength(buf,SPS*2);
  fillchar(buf[0],SPS*2,2);
  ...
  // no need to free buf[] memory (it is done by the compiler)
end;

David Heffernan · Accepted Answer · 2011-11-01T13:56:05.583

1

Perhaps like this:

var
  buf: array of AnsiChar;
  a: PAnsiChar;
...
SetLength(buf, SPS*2);
FillChar(buf[0], Length(buf), 2);
a := @buf[0];

No idea what answers is, but, assuming it is a char in your C++ code then you would write it like this:

var
  answers: AnsiChar;
...
answers := buf[2];

edited Nov 01 '11 at 13:56

answered Nov 01 '11 at 12:17

David Heffernan

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can i use instead of array of AnsiChar into array of Byte? – user558126 Nov 01 '11 at 12:20
They are pretty much interchangeable. But if you want to treat as a `PAnsiChar` then you'd need a cast. Nothing much to be gained by using `Byte` rather than `AnsiChar` I suspect. – David Heffernan Nov 01 '11 at 12:21
dynamic array only makes things worse, `PChar^` and `PByte^` are arrays already (BTW, this is C++, not C) – Premature Optimization Nov 01 '11 at 13:51
3

@premature What are you talking about? What's wrong with dynamic arrays? They are an excellent match to C++ new[]. Where you propose getting the buffer from? – David Heffernan Nov 01 '11 at 13:57

Translate unsigned char *buf=NULL to Pascal?

2 Answers2