Need to get data in .dat and convert it into System::string

[IdiotLam]

I am trying to make a log in system which load data from a .dat
So i have a part of code below

if(radioButton1->Checked)	//Login
{
String ^ userAC = textBox1->Text;
String ^ userPW = textBox2->Text;
char ACc[300];
char PWc[300];
bool OK=false;
ifstream inFile("Login System.dat", ios::in);
if (!inFile)
{
   MessageBox::Show("File could not be opened\nError code: 4", "Error", MessageBoxButtons::OK);
inFile.close();
}
else
{
while(inFile>>ACc>>PWc)
{
							
/**/
string AC(ACc);
string PW(PWc);
String ^ ACstr;
String ^ PWstr;
MarshalString(ACstr,AC);
MarshalString(PWstr,PW);
/**/
if (userAC==ACstr && userPW==PWstr)
{
	OK=true;
	MessageBox::Show("Welcome Back!\n"+ACstr,"Login",MessageBoxButtons::OK);
	break;
}

}
if (OK==false)
{
MessageBox::Show("Cannot login\nIncorrect Username or Password", "Login", MessageBoxButtons::OK);
}
						
}

}

I built it and it is a success but when i run it,

it have error:
Debug Assertion Failed!

Program:....
File:....\Microsoft Visual Studio 10.0\VC\include\xstring
Line: 930

Expression: invalid null pointer

.......

I have no idea what is going wrong so i try to comment some part to debug
I found that it come form the code

string AC(ACc);
string PW(PWc);
String ^ ACstr;
String ^ PWstr;
MarshalString(ACstr,AC);
MarshalString(PWstr,PW);

I tried to use std::string and System::string when getting data from .dat but it failed so i tried char allay

And i just want to find a way to finish this thing with by any mean

[IdiotLam]

I have found the problem
MarshalString can only convert System::string to std::string
I have used it wrongly

String ^ AC = gcnew String(AC.c_str())
String ^ PW = gcnew String(PW.c_str())

This can save the day.

[MiiNiPaa]

Just to note: This is not C++. It is C++/CLI: Microsoft created language which is different from C++.

You are unlikely to get help on it here, but you can try your luck in Windows Programming if you want.