How to properly hook into an instance variable with theos

 cell = [[[%c(SBSearchTableViewCell) alloc] initWithStyle:(UITableViewCellStyleDefault) reuseIdentifier:@"dude"] autorelease];
 float &secWidth = MSHookIvar(cell, "_sectionHeaderWidth");
 if (secWidth) {
    secWidth = sectionHeaderWidth;
 }

Not the %c to get the class and the & in front of secWidth. This makes sure you are getting a reference.