What happens to the Users/username/Library directory. Why can't I change the current directory?

Question

I was following a code sample from "Programming in Objective-C Fourth Edition" by Stephen Kochan.

The program looks for a file, and performs a few things on it:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSString *fName = @"testfile";
        NSFileManager *fm;
        NSDictionary *attr;

        //Need to create an instance of the file manager

        fm = [NSFileManager defaultManager];

        //Let's make sure our test file exists first


        NSLog([fm currentDirectoryPath]);

        if ([fm fileExistsAtPath: fName] == NO) {
            NSLog(@"File doesn't exist!");
            return 1;
        }

        //now lets make a copy

        if ([fm copyItemAtPath: fName toPath: @"newfile" error: NULL]) {
            NSLog(@"File Copy failed!");
            return 2;
        }

        //Now let's see test to see if the two files are equal

        if ([fm contentsEqualAtPath: fName andPath: @"newfile"] == NO) {
            NSLog(@"Files are Not Equal!");
            return 3;
        }

        //Now lets rename the copy
        if ([fm moveItemAtPath: @"newfile" toPath: @"newfile2" error: NULL] == NO) {
            NSLog(@"File rename Failed");
            return 4;
        }

        //get the size of the newfile2

        if((attr = [fm attributesOfItemAtPath: @"newfile2" error: NULL]) == nil)
        {
            NSLog(@"Couldn't get file attributes");
            return 5;
        }

        NSLog(@"File size is %llu bytes", [[attr objectForKey: NSFileSize] unsignedLongLongValue]);

        //And finally, let's delete the original file

        if([fm removeItemAtPath: fName error: NULL])
        {
            NSLog(@"file removal failed");
            return 6;
        }

        NSLog(@"All operations were successful");

        //Display the contents of the newly-createed file

        NSLog(@" %@", [NSString stringWithContentsOfFile: @"newfile2" encoding:NSUTF8StringEncoding error: NULL]);
    }
    return 0;
}

I created a file named "testfile" and placed it in project directory. When I ran the program, It couldn't find the file. I added [NSFileManager currentDirectoryPath] to check the current path which was apparently something like this:

/Users/myusername/Library/Developer/Xcode/DerivedData/Prog_16.1-eekphhgfzdjviqauolqexkowfqfg/Build/Products/Debug

I went looking for the Library directory, but it doesn't exist. Is this some temporary directory that's created when the program is running, then deleted after it exits?

Edit: I've tried changing the path of the current directory using [NSFileManager changeCurrentDirectoryPath: newPath] and it fails to change the path. I tried setting to newPath to @"Users/username/Desktop" and that fails too!

Answer 1

The Library directory does exist but it is hidden as standard. Open up the terminal and type the command: chflags nohidden ~/Library/.

Then look again and it will be magically there!

Edit: for programming with NSFileManager there's a very useful function: NSSearchPathForDirectoriesInDomains(). E.g. To get the desktop do directory:

NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDesktopDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"test.txt"];
NSString *test = @"hello";
[test writeToFile:path atomicallly:YES];

This will write a little txt file to your desktop. (As long as you app isn't sandboxed).

Hope this helps.

Answer 2

When you place a file in the project directory, it gets shipped as part of the app's bundle. To get at the bundle directory tree, use NSBundle...

// use the file extension (if any) for the ofType: param
NSString *path = [[NSBundle mainBundle] pathForResource:@"testfile" ofType:@""];
if ([[NSFileManager defaultManager] fileExistsAtPath:path]) {
    NSLog(@"there it is!  %@", path);
}