Import Delphi DLL function into C++ Builder , transfer PAnsiChar - c++

Question

I want to use Delphi code , export via DLL from C++ Builder
Delphi Code fragment goes like this
// function declare
function NameData(ItemIndex: Integer;
Buffer: PAnsiChar; var BufSize: DWORD): DWORD; stdcall;
external 'database.dll'
// function calling code
s1, S2: AnsiString;
begin
for i := 1 to ... do
begin
BufSize := 0;
NameData(i, nil, BufSize);
SetLength(s1, BufSize);
NameData(i, PAnsiChar(s1), BufSize);
mmo_dll.lines.Add(' name -> ' + string(s1));
relevant DLL code
library DLLCode;
function NameData(ItemIndex: Integer;
Buffer: PAnsiChar; var BufSize: DWORD): DWORD; stdcall;
var
returnString: Ansistring;
begin
returnString := ' call some other functions .....';
if BufSize < Length(returnString) then
result := ERROR_BUFFER_TOO_SMALL
else
begin
StrPCopy(Buffer, returnString);
result := ERROR_NO_ERROR;
end;
BufSize := Length(returnString);
end;
this and a lot of more stuff works fine, Delphi and Delphi DLL.
Now here is my not working C++ code :
// function prototype
typedef void (__stdcall*IntCharIntIn_VoidOut)(int, PAnsiChar, int);
// DLL prototype
extern "C" __declspec(dllimport)
IntCharIntIn_VoidOut __stdcall NameData(int, PAnsiChar, int);
// instance declaration
IntCharIntIn_VoidOut NameData;
// load library data, no error raise, other simpler function call already working
........
NameData = (IntCharIntIn_VoidOut)::GetProcAddress(load,
"NameData");
/// calling code
int Bufsize;
PAnsiChar DataName;
for (i = 0; i < count - 1; i++) {
*Bufsize = 0;
NameData(i, NULL, Bufsize);
StrLen(SignalName);
NameData(i, DataName, Bufsize );
Memo1->Lines->Add(IntToStr(i)); // for test only
}
In the second call I get an access violation, but can't see why/where I'm wrong

Answer 1

You don't allocate any memory, and your function declaration is wrong.
The function really should be declared like so:
typedef void (__stdcall *IntCharIntIn_VoidOut)(int, char*, unsigned int*);
And your calling code should be:
unsigned int Bufsize;
char* DataName;
for (i = 0; i < count - 1; i++) {
Bufsize = 0;
NameData(i, NULL, &Bufsize);
DataName = new char[Bufsize + 1];
NameData(i, DataName, &Bufsize);
// do something with DataName
delete[] DataName;
}
I've omitted error checking on the memory allocation and deallocation. If it were me I would be using grown up C++ string objects and not raw memory. The loop looks like it misses the final iteration, should be <= count - 1 or < count surely. Your type name, IntCharIntIn_VoidOut fails to recognise that two of the arguments are pointers. I'm using char* rather than PAnsiChar, but I guess that the latter is just an alias to the former.
I'll leave all of the above for you to deal with.