CFileDialog constructor can't spot TRUE and fopen(str,"r") error - fopen

Question

I call the CFileDialog constructor in the following method:
CFileDialog FileDlg(TRUE, ".txt", NULL, 0, strFilter);
according to the parameters in the CFileDialog constructor, the first parameter should be BOOL, but my compiler thinks it's int instead of BOOL. Can you tell me why?
Besides, in the code, when I use fopen(str,"r"), the error is no conversion function from CSring to const char*. Appreciate your discussion.
The code is:
void OnFileOpen()
{
CClientDC dc(this);
CString str;
CRect rc;
FILE *ifp;
char strFilter[] = { "TXT Files (*.txt)|*.txt|All Files(*.*)|*.*||" };
CFileDialog FileDlg(TRUE, ".txt", NULL, 0, strFilter);
if (FileDlg.DoModal() == IDOK)
{
str = FileDlg.GetFileName();
ifp = fopen(str,"r");
dc.TextOutW(350, 50, "File Opened: " + str);
for (int i = 1; i < n; i++)
{
fscanf(ifp, "%d %d", &pt[i].x, &pt[i].y);
rc = CRect(pt[i].x - 30, pt[i].y - 30, pt[i].x + 30, pt[i].y + 30);
dc.Ellipse(rc);
rc = CRect(pt[i].x - 1, pt[i].y - 1, pt[i].x + 1, pt[i].y + 1);
dc.Rectangle(rc);
}
fclose(ifp);
}
}