Access violation when calling an external function (C ++) from a Delphi application

Question

I have an external DLL written in C ++. The fragment below declares the type of structure and function, which, specifying a pointer, fills a variable of this type:

enum LimitType { NoLimit, PotLimit, FixedLimit };

struct SScraperState
{
    char        title[512];
    unsigned int    card_common[5];
    unsigned int    card_player[10][2];
    unsigned int    card_player_for_display[2];
    bool        dealer[10];
    bool        sitting_out[10];
    CString     seated[10];
    CString     active[10];
    CString     name[10];
    double      balance[10];
    bool        name_good_scrape[10];
    bool        balance_good_scrape[10];
    double      bet[10];
    double      pot[10];
    CString     button_state[10];
    CString     i86X_button_state[10];
    CString     i86_button_state;
    CString     button_label[10];
    double      sblind;
    double      bblind;
    double      bbet;
    double      ante;
    LimitType   limit;
    double      handnumber;
    bool        istournament;
};

extern "C" {
    SCRAPER_API int ScraperScrape(HWND hwnd, SScraperState *state);
}

I declare a similar type in my Delphi application and call the above function:

interface

type
  LimitType = (NoLimit, PotLimit, FixedLimit);

  SScraperState = record
    title: Array [0..511] of Char;
    card_common: Array [0..4] of Word;
    card_player: Array [0..9, 0..1] of Word;
    card_player_for_display: Array [0..1] of Word;
    dealer: Array [0..9] of Boolean;
    sitting_out: Array [0..9] of Boolean;
    seated: Array [0..9] of String;
    active: Array [0..9] of String;
    name: Array [0..9] of String;
    balance: Array [0..9] of Double;
    name_good_scrape: Array [0..9] of Boolean;
    balance_good_scrape: Array [0..9] of Boolean;
    bet: Array [0..9] of Double;
    pot: Array [0..9] of Double;
    button_state: Array [0..9] of String;
    i86X_button_state: Array [0..9] of String;
    i86_button_state: String;
    button_label: Array [0..9] of String;
    sblind: Double;
    bblind: Double;
    bbet: Double;
    ante: Double;
    limit: LimitType;
    handnumber: Double;
    istournament: Boolean;
  end;

  pSScraperState = ^SScraperState;

function ScraperScrape(hWnd: HWND; State: pSScraperState): Integer; cdecl; external 'Scraper.dll';

implementation

var
  CurState: SScraperState;
  pCurState: pSScraperState;

  if ScraperScrape(hWnd, pCurState) = 0 then
  ...

When a function is called, I get a debugger exception notification:

Project ... EAccessViolation exception class with the message "Access violation at address 10103F68 in the module" Scraper.dll ". Reading address FFFFFFFC '. The process stopped.

, DLL, , , . , .

Answer 1

, ++ CString Delphi String .

, , C-Style (PChar Delphi).

++ - :

char Dealer[100][10];

, , - , C-

Delphi

Dealer : packed array[0..9, 0..99] of char; 

type 
  TDealer = packed array[0..99] of char;
  ...
  Dealer : arry[0..9] of TDealer;

C- (TCHAR API)

Dealer: array[0..9] of PAnsiChar; // or PWideChar if source is UCS-16

, String, Char (, , PChar) (UCS 16) Delphi 2009.

, , Delphi Word 16 , ++. , , Windows API, USHORT "unsigned int" Word

Answer 2

, , , . 16- ++, unsigned int 16- , Delphi Word. Cardinal. Delphi 2009 , Char ; AnsiChar.

, , . ++ Microsoft CString. Delphi , Microsoft-++, . Delphi string , . .

.

- DLL, , DLL, - . , . DLL , . API .

, DLL- ++, ++ , , ++.

Answer 3

DLL , CString PAnsiChar ( PWideChar, DLL Unicode), :

type
  LimitType = ( NoLimit, PotLimit, FixedLimit );

  SScraperState = record
    title: array[0..511] of AnsiChar;
    card_common: array[0..4] of Cardinal;
    card_player: array[0..9, 0..1] of Cardinal;
    card_player_for_display: array[0..1] of Cardinal;
    dealer: array[0..9] of Boolean;
    sitting_out: array[0..9] of Boolean;
    seated: array[0..9] of PAnsiChar;
    active: array[0..9] of PAnsiChar;
    name: array[0..9] of PAnsiChar;
    balance: array[0..9] of Double;
    name_good_scrape[0..9] of Boolean;
    balance_good_scrape[0..9] of Boolean;
    bet: array[0..9] of Double;
    pot: array[0.99]: Double;
    button_state: array[0.9] of PAnsiChar;
    i86X_button_state: array[0..9] of PAnsiChar;
    i86_button_state: PAnsiChar;
    button_label: array[0..9] of PAnsiChar;
    sblind: Double;
    bblind: Double;
    bbet: Double;
    ante: Double;
    limit: LimitType;
    handnumber: Double;
    istournament: Boolean; 
  end; 

, , , , ScraperScrape(). Delphi , :

...
pSScraperState = ^SScraperState;       

function ScraperScrape(wnd: HWND; state: pSScraperState): Integer; cdecl; external 'Scraper.dll';  

...

var
  CurState: SScraperState;        
  pCurState: pSScraperState;        
begin        
  pCurState := @CurState;
  if ScraperScrape(hWnd, pCurState) = 0 then  
    ...
end;

pCurState:

var
  CurState: SScraperState;        
begin        
  if ScraperScrape(hWnd, @CurState) = 0 then  
    ...
end;

It would be better to completely get rid of the pSScraperState alias:

function ScraperScrape(wnd: HWND; var state: SScraperState): Integer; cdecl; external 'Scraper.dll';  

var
  CurState: SScraperState;        
begin        
  if ScraperScrape(hWnd, CurState) = 0 then  
    ...
end;