在我的DLL中的Delphi中,我必须分配一个函数的return pchar

function GetAString(Buffer: PChar; BufLen: Integer): Integer; stdcall;
var
  S: String;
begin
  S := SomeFuncThatReturnsString;
  Result := Min(BufLen,Length(S));
  if (Buffer <> nil) and (Result > 0) then
    Move(S[1],Buffer^,Result * SizeOf(Char));
end;

这允许应用程序决定何时以及如何分配内存(堆栈与堆,重用内存块等)：

var
  S: String;
begin
  SetLength(S,256);
  SetLength(S,GetAString(PChar(S),256));
  ...
end;

var
  S: String;
begin
  SetLength(S,GetAString(nil,0));
  if Length(S) > 0 then GetAString(PChar(S),Length(S));
  ...
end;

var
  S: arraY[0..255] of Char;
  Len: Integer;
begin
  Len := GetAString(S,256);
  ...
end;

如果这不适合您,那么您需要让DLL分配内存,将其返回给应用程序使用,然后让DLL导出一个额外的函数,当完成传递指针时应用程序可以调用该函数回到DLL中解放：

function GetAString: PChar; stdcall;
var
  S: String;
begin
  S := SomeFuncThatReturnsString;
  if S <> '' then
  begin
    Result := StrAlloc(Length(S)+1);
    StrPCopy(Result,S);
  end else
    Result := nil;
end;

procedure FreeAString(AStr: PChar); stdcall;
begin
  StrDispose(AStr);
end;

var
  S: PChar;
begin
  S := GetAString;
  if S <> nil then
  try
    ...
  finally
    FreeAString(S);
  end;
end;