getenv - any solutions?_(re)

Thu, 24 Oct 96 15:58:33 CST

On Wed, 23 Oct 1996 02:03:57 -0400 (EDT), 
John Michael Black   wrote:

>There's been a lot of getenvs going around here lately. :)  Has anyone
>found a method that works yet?  The last thing posted about it gave this:
>
>        Function GetEnv ( Name: __CString__ ): PChar; C;
>
>GPC does not recognize PChar -- at least ours doesn't.
>
>This could go on for weeks.... :)

Naah....

Take this:


(*
 * Demonstrate the conversion of "Pascal" string schemas to "C" style
 * strings and back, and calling an external "C" style function.
 *
 * J.J. van der Heijden 
 *)

Program EnvDemo;

type
  word = __unsigned__ integer;
  TString = string(256);        { Pascal string schema }
  CString = __cstring__;        { C style string }

{ Convert a "C" string to a "Pascal" string }
function StrPas(Src: CString): TString;
var
  S : TString;
begin
  S := '';
  if (Src <> NIL)
  then while ( (Src^ <> chr(0)) AND (length(S) < S.capacity)) do
   begin
     S := S + Src^;
     inc(Word(Src));
   end;
  StrPas := S;
end;

{ Convert a "Pascal" string to a "C" string }
function StrPCopy(Dest: CString; Src: String): CString;
var
  c: integer;
  p : CString;
begin
  p := Dest;
  for c:=1 to length(Src) do
  begin
    p^ := Src[c];
    inc(word(p))
  end;
  p^ := chr(0);
  StrPCopy := Dest;
end;

{ C library function prototype: char *getenv(const char *name); }
function GetEnv(name : CString): CString; C;

var
  pName: CString;

begin
  getmem(pName, 256);

  pName := StrPCopy(pName, 'USER');
  writeln('Hello ', StrPas(GetEnv(pName)), ' !');

  pName := StrPCopy(pName, 'PATH');
  writeln('Your PATH is: ', StrPas(GetEnv(pName)));

  freemem(pName, 256);
end.

There are multiple ways to do this: for example, you can also declare a 

    type PChar = ^char;

and replace every instance of CString with PChar. Works great.
Do not pass a CString argument as a "var" if it's declared as "const char *"
in C; you will definately get a coredump. (in C too BTW)

I tested this with Linux and djgpp (dos) GPC, 1.2 prerelease.
The GPC-1.1 may have troubles with the function returning a TString schema.
Let me know if it doesn't work for you, though I can't imagine that.

JanJaap

---
"Nothing shocks me, I'm a scientist", Indiana Jones

J.J. van der Heijden (j.j.vanderheijden@student.utwente.nl)