Drop-in fopen replacement for iOS applications that prepends the documents directory to file paths.

utilities.h

//
//  utilities.h
//

#include <stdio.h>

#ifndef MyProject_utilities_h
#define MyProject_utilities_h

FILE *iosfopen(const char *filename, const char *mode);

#endif

utilities.m

//
//  utilities.m
//

#include "utilities.h"
#include <Foundation/Foundation.h>

FILE *iosfopen(const char *filename, const char *mode) {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    
    NSString *fileString = [NSString stringWithCString:filename encoding:NSASCIIStringEncoding];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:fileString];
    const char *filePath = [path cStringUsingEncoding:NSASCIIStringEncoding];

    return fopen(filePath, mode);
}