Pointer to member function in struct

Dean Seo

Hi, Since I knew The Code Project, it has been helpful a lot. Now I think I have a small misunderstanding about pointer to member function in a struct and I need your help, which will be priceless to me. I am simply trying to see how pointer to member function works and it seems a little tricky. The code I am having a problem with is below.

#include #include #define KEY_ESC 27

using std::cout;
using std::endl;

class CAccount;

struct StateMap
{
int input;
void (CAccount::*mfp)();
};

class CAccount
{
public:
enum
{
STATE_IDLE,
STATE_INPUT,
STATE_WAIT_ACK
};

public:
StateMap map[3];
int m_iState;

CAccount();

void OnIdle();
void OnInput();
void OnWaitAck();

};//class CAccount

CAccount::CAccount(){
map[0].input = 1;
map[0].mfp = &CAccount::OnIdle;

map\[1\].input = 2;
map\[1\].mfp = &CAccount::OnInput;

map\[2\].input = 3;
map\[2\].mfp = &CAccount::OnWaitAck;

m\_iState = STATE\_IDLE;

}

void CAccount::OnIdle()
{
cout << "OnIdle()" << endl;
}

void CAccount::OnInput()
{
cout << "OnInput()" << endl;
}

void CAccount::OnWaitAck()
{
cout << "OnWaitAck()" << endl;
}

int main()
{
int ch = 0;
int i;
CAccount account;

while ( ch != KEY\_ESC )
{
	ch = \_getch();
	i  = 0;
	while ( account.map\[i\].input != 0 )
	{
		if ( ch == account.map\[i\].input )
		{
			(account.(map\[i\].\*mfp))(); // compile error
		}//if
		i++;
	}//while
}//while

return 0;

}//main()

I just don't know the right syntax for that part. How should I change that error line to make it work? Thanks in advance.

Eugen Podsypalnikov

Try the following :) :

//...
typedef void (*LPSTATEPROC) (void);

struct StateMap
{
int input;
LPSTATEPROC mfp;
};
//...

They sought it with thimbles, they sought it with care; They pursued it with forks and hope; They threatened its life with a railway-share; They charmed it with smiles and soap. :)

Dean Seo

Thanks.

Eugen Podsypalnikov wrote:

typedef void (*LPSTATEPROC) (void);

You meant this, right?

typedef void (CAccount::*LPSTATEPROC) (void);

But it seems like it doesn't still work and the error occurs at the same line.

#include
#include

#define KEY_ESC 27

using std::cout;
using std::endl;

class CAccount;

typedef void (CAccount::*LPSTATEPROC) (void);

struct StateMap
{
int input;
LPSTATEPROC mfp;
};
class CAccount
{
public:
enum
{
STATE_IDLE,
STATE_INPUT,
STATE_WAIT_ACK
};

public:
StateMap map[3];
int m_iState;

CAccount();

void OnIdle();
void OnInput();
void OnWaitAck();

};//class CAccount

CAccount::CAccount(){
map[0].input = 1;
map[0].mfp = &CAccount::OnIdle;

map\[1\].input = 2;
map\[1\].mfp = &CAccount::OnInput;

map\[2\].input = 3;
map\[2\].mfp = &CAccount::OnWaitAck;

m\_iState = STATE\_IDLE;

}

void CAccount::OnIdle()
{
cout << "OnIdle()" << endl;
}

void CAccount::OnInput()
{
cout << "OnInput()" << endl;
}

void CAccount::OnWaitAck()
{
cout << "OnWaitAck()" << endl;
}

int main()
{
int ch = 0;
int i;
CAccount account;

while ( ch != KEY\_ESC )
{
	ch = \_getch();
	i  = 0;
	while ( account.map\[i\].input != 0 )
	{
		if ( ch == account.map\[i\].input )
		{
			(account.(map\[i\].\*mfp))(); // compile error
		}//if
		i++;
	}//while
}//while

return 0;

}//main()

How can I change that error line to make it work? Thanks!

Dean Seo

Hi, I just figured it out myself. But your reply helped me a lot to figure out to make it work! Thank you so much.

Lost User

I think the line:

			(account.(map\[i\].\*mfp))(); // compile error

should not use indirection, and should read:

			(account.(map\[i\].mfp))();

Unrequited desire is character building. OriginalGriff

Chang Su Lee

it is error too!

Lost User

What error?

Unrequited desire is character building. OriginalGriff