cin >> a char *, because string doesnt work

Hello all,

I am developing an application using OpenCV that requires the user to specify the name of an image file, which then gets loaded using cvLoadImage ();

cvLoadImage takes a (char *) as an argument- how do i have the user create one of these? the following code created a segfault:

IplImage * img;
char * filename;
cin >> filename;
img = cvLoadImage (filename);

thanks!