I am having problems using the string variable...

I am using it like this:

Code:
void ErrorMsg( string emsg )
{
    MessageBox( emsg, "", MB_OK );
}
it give me the error: MessageBoxA cannot convert basic_string to const char *.

How do i use a string variable for this kind of situation... There are other functions that i am trying to do this with that all give the same error... Can anyone help???