Ios7.1 Prefix.pch not working

Question

In my project I can not find the Prefix.pch file, so I create a new one, and the Build Setting - prefix header adds the path and file name to it projectdir / projectname-Prefix.pch

#ifdef __OBJC__
#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>


#define APP_FONT(fontSize) [UIFont systemFontOfSize:fontSize]
#endif

I can install the font without warning error label.font = APP_FONT (18);

However, it crashes while running, APP_FONT (18) returns zero.

The problem does not work on ios8