library DemoDll;

uses

  SysUtils, Classes, Windows, StrUtils;

{$R *.res}

// Write to log file

procedure AddLog(const AFormat: string; Args: array of const); overload;

var

  LogFile: TextFile;

  FileName: string;

begin

  FileName := GetEnvironmentVariable('TEMP') + '\DemoDll.log';

  try

    AssignFile(LogFile, FileName);

    if FileExists(FileName) then

      Append(LogFile)

    else

      ReWrite(LogFile);

    Writeln(LogFile, Format('[%s] ', [DateTimeToStr(Now)]) + Format(AFormat, Args));

  finally

    CloseFile(LogFile);

  end;

end;

// Write to log file

procedure AddLog(const AFormat: string); overload;

begin

  AddLog(AFormat, []);

end;

// return a+b

function TestAdd(a, b: Integer): Integer; stdcall;

begin

  AddLog('TestAdd(%d,%d)', [a, b]);

  Result := a + b;

end;

// do nothing, just log input string

function TestInputStr(PInStr: PChar): Integer; stdcall;

var

  str: string;

begin

  str := StrPas(PInStr);

  AddLog('TestInputStr(%s)', [str]);

  Result := 0;

end;

// reverse first string and write to second string

function TestOutputStr(PInStr, POutStr: PChar): Integer; stdcall;

var

  str: string;

begin

  str := StrPas(PInStr);

  str := ReverseString(str);

  StrCopy(POutStr, PChar(str));

  AddLog('TestOutputStr(%s)', [str]);

  Result := 0;

end;

exports

  TestAdd,

  TestInputStr,

  TestOutputStr;

begin

  AddLog('BEGIN');

end.

// Put DemoDll.dll in the same dir

// DemoDll.dll is developed by Delphi

#include "windows.h"

#include <iostream>

typedef int(__stdcall  *fTestAdd)(int, int);

typedef int(__stdcall  *fTestInputStr)(char *);

typedef int(__stdcall  *fTestOutputStr)(char *, char *);

using namespace std;

int main(int argc, char* argv[])

{

    HINSTANCE       hDllLibrary = NULL;

    fTestAdd        TestAdd = NULL;

    fTestInputStr   TestInputStr = NULL;

    fTestOutputStr  TestOutputStr = NULL;

    hDllLibrary = LoadLibraryA("DemoDll.dll");

    if (hDllLibrary){

        TestAdd = (fTestAdd)GetProcAddress(hDllLibrary, "TestAdd");

        TestInputStr = (fTestInputStr)GetProcAddress(hDllLibrary, "TestInputStr");

        TestOutputStr = (fTestOutputStr)GetProcAddress(hDllLibrary, "TestOutputStr");

        // check if a == 3

        int a = TestAdd(1, 2);

        cout << "TestAdd(1,2)=" << a << endl;

        // check if input string has output to log file

        char b[] = "nothing";

        TestInputStr(b);

        cout << "TestInputStr(" << b << ")" << endl;

        // check if output string is reversed

        char c[] = "nothing";

        char d[256] = { 0 };

        TestOutputStr(c, d);

        cout << "TestOutputStr(" << c << ")=" << d << endl;

    }

    getchar();

    return 0;

}

// Console output:

//

// TestAdd(1, 2) = 3

// TestInputStr(nothing)

// TestOutputStr(nothing) = gnihton

//

// %Temp%/DemoDll.log

//[2017 / 6 / 4 14:48 : 46] BEGIN

//[2017 / 6 / 4 14:48 : 46] TestAdd(1, 2)

//[2017 / 6 / 4 14:48 : 46] TestInputStr(nothing)

//[2017 / 6 / 4 14:48 : 46] TestOutputStr(gnihton)