Question

The code is copied below. I am using the documents directory because I know you can write outside of your apps sandbox.
I also compare the string I was using to determine the path to one created by the NSFileManager and they are the same. What do you all think?

- (NSString *)documentsDirectory
{
    NSArray *paths=NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);

    return [paths objectAtIndex:0];
}

- (void) whateverFunction{
    NSString *memfileName = @"memmapfile.map";

    NSString *filePath = [[self documentsDirectory] stringByAppendingPathComponent:memfileName];

    NSLog(@"Here is the filePath: %@", filePath);

    NSLog(@"Other        version: %s", [[NSFileManager defaultManager] fileSystemRepresentationWithPath:filePath]);
    int memFD = open([filePath cStringUsingEncoding:NSASCIIStringEncoding], O_RDWR);
    NSLog(@"I am getting -1 for memFD: %d", memFD);
}

Answer 1

I’d guess your file doesn’t exist yet, so of course you can’t open it. You should add O_CREAT to your open flags so that it gets created if it doesn’t exist:

int memFD = open([filePath cStringUsingEncoding:NSASCIIStringEncoding], O_RDWR|O_CREAT);