I am trying to initialize a multidimensional array from a file using C for a iPhone 4inch app but I can't open up the file using fopen.
Whenever I try this I get a NULL:
FILE *f;
f=fopen("/level1.rez", "r");
if (f == NULL)
{
printf("Error Reading File\n");
//exit (0);
}
I am not sure how to open files using C.
I tried this already:
I printed out the current working directory using getcwd but all I got was "/" and when I attached that to the file name I still got NULL.
I read that if you go to product > scheme > edit scheme then options you can change the current working directory but I don't see that option.
Also I read that you can use absolute paths like: /users/name/desktop/program
but I am new to iOS development so I don't know if that is a good idea.
So how do I get fopen to work?
You CAN specify absolute paths in iOS, but the path in your example is probably used in Mac OS, which is laid out a little differently. You can specify paths to fopen() as you say, but there is more work to finding out what the first part of that path really is.
The iOS puts all AppStore apps into folders with randomly generated sandbox directory names. It is basically the the hexadecimal string of a GUID. So you need to use methods from iOS frameworks to get the first part of the path (or URL) to your file.
If the file is part of the app bundle so it can ship with the app, then you will need to use NSBundle methods to find the path to the file.
If the file is generated or downloaded after the app starts up on the device, then you need to use NSFileManager methods to determine the path to the directory of the file. (Typically the Documents directory. You can build a directory structure of your choice within the sandbox.)
Related
My iOS app is writing to local files to:
/var/mobile/Containers/Data/Application/A.../Library/a.txt
When my app updates, it gets a new application container ID and folder:
/var/mobile/Containers/Data/Application/B...
What happens to all the files I wrote to container ID A?
Is there an "update hook" that will allow me to copy all the "A" container files to path "B"?
Can the new version of the app (B) read the old versions files (A)?
Is there any documentation around what happens to the filesystem during updates?
Is it possible to recover files from container A after B has been installed?
When you update an app, by changing its version number in the .plist file, iOS creates a new directory for that app with a different hexadecimal name and it copies all the files to the new directories. Now if you are using the absolute paths to get the details of files from the directories then those paths would be incorrect and you won't get the file details.
I just tried this in simulator. I created a function as below which will return the document directory path url
func getDocumentsDirectory() -> URL {
let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
let documentsDirectory = paths[0]
return documentsDirectory
}
I called this function from didFinishLaunchingWithOptions in app delegate when version number was 1.0 and it returned the below path :
file:///Users/BhargavRathod/Library/Developer/CoreSimulator/Devices/3082611F-BCCA-4D17-B390-E0EF4CA454DA/data/Containers/Data/Application/72759097-38F3-4292-825E-1D2343219973/Documents/
When I updated the version number to 1.1 it returned me the new path as :
file:///Users/BhargavRathod/Library/Developer/CoreSimulator/Devices/3082611F-BCCA-4D17-B390-E0EF4CA454DA/data/Containers/Data/Application/72DC31E9-C32F-42CC-8449-F1946ADB1018/Documents/
So if you are using a absolute path to access any file from document directory then it is not good practice. You can just save the file name(or relative path after the document directory) and whenever the access to that file name is required then get the file name and append it after the document directory path and access the file.
I hope this will be of some help to you.
My iOS app is writing to local files to: /var/mobile/Containers/Data/Application/A.../Library/a.txt
Okay, stop right there. This is wrong.
Your app has its own sandbox. This sandbox persists forever, thru updates, as long as your app keeps its Bundle ID, and as long as the user does not delete the app.
You thus have no business knowing or thinking about the full absolute path to where your file is. All you know, and all you need to know, is that it is in your app’s sandbox in the Library directory. You can, at any time, obtain the URL of the Library directory by means of its search path:
https://developer.apple.com/documentation/foundation/filemanager/searchpathdirectory/librarydirectory
And that is where the file will always be. As long as you ask the FileManager for your Library directory and for the a.txt file within it, you will find the same file, regardless of any updates, as long as the user doesn’t actually delete your app (because that deletes the sandbox).
Can explain what happens to the files
Nothing. They stay where they are within the sandbox. The absolute URL of the sandbox may change, but your files are unaffected.
how to keep the files written by the previous version of the app
They are kept automatically. You don’t have to do anything.
(Having said all that, keep in mind that if you submit an app with a different bundle id, that is not a new version of your app. It is a totally different app. In that case you would have a very different problem to solve. This would be no different from any other problem of communicating files from one app to another. You’d need to put the files in a common location, make them available thru the Document Browser, make them exportable by the user, or whatever.)
I have a data file that I need to include with my app when I distribute it. When loading any files in the app, I prefix the file name with:
Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)
This works great for anything I create within the app (and for reading back), like files I download in response to a user action. But I can't for the life of me figure out how to place files there when I build my app in Visual Studio.
I've tried making a "Documents" subdirectory in the special "Resources" folder, but that didn't work (I tried setting the "Build Action" to both BundleResource and Content). When I look at the folder for my app (from using the simulator) I can see that in the "Documents" folder there's all the files I downloaded, but I can't find my data file that I'm trying to bundle ahead of time. I even searched my entire hard drive on the Mac and still couldn't find said data file.
The data file isn't an image, if it matters. Just raw binary data. How do I set it up so that this file goes into the proper documents directory at compile time, so that I can read it using the SpecialFolder.MyDocuments prefix? Thanks.
You can't. You can include files in your app bundle, and then at startup copy them from the bundle into a user folder. But this won't happen automatically.
I am using Cordova fileSystem to download some mp3 Audio files thru my App. I am using cordova.file.cacheDirectory and creating a subfolder within that to store the downloaded files. However, the problem is that each time I make some changes and run the App on iPad I get a different path.
The usual pattern is
file:///var/mobile/Containers/Data/Application/13E9EA83-94A2-4950-811E-E491AC176A78/Library/Caches/MyFolder/MyFiles.mp3
However the long number (App UUID) is not consistent. It changes each time I run the App on iPad through Xcode. Because of this I am unable to access, play, delete any files downloaded during the previous session because I am saving the file names with absolute path in a separate file for quick access in the future.
After some R&D I have realized that even though UUID changes each time, it actually refers to the same location. Hence the solution is not to save absolute path and instead, save only the Path beyond "/MyFolder/" in the above example. Each time when the App is run, the Base Path, which is actually file.cordova.cacheDirectory, should be appended to each entry to obtain the absolute Path to the file.
I've developed an application and I need to remove my computer local path from the generated iPA file.
I did the following:
unzipping iPA file.
click on show package content.
open exec(appname.exec) file with text editor.
Now I can see some binary stuff, and strings with my computer local path (with my mac name).
I have to remove these paths from the exec file, due to security issues. How can I do so?
As Accessing Files and Directories says:
Although you can open any file and read its contents as a stream of bytes, doing so is not always the right choice. OS X and iOS provide built-in support that makes opening many types of standard file formats (such as text files, images, sounds, and property lists) much easier. For these standard file formats, you should use the higher-level options for reading and writing the file contents. Table 2-1 lists the common file types supported by the system along with information about how you access them.
You have many ways to save your data:
Specifying the Path to a File or Directory
Locating Items in Your App Bundle
Locating Items in the Standard Directories
Locating Files Using Bookmarks
You have chosen to Specifying the Path to a File or Directory,as #Droppy says
Firstly it will break the code signature and secondly it's time consuming and error prone.
You'd better choose to Locating Items in the Standard Directories
Here is why you should choose the way:
Locating Items in the Standard Directories
When you need to locate a file in one of the standard directories, use the system frameworks to locate the directory first and then use the resulting URL to build a path to the file. The Foundation framework includes several options for locating the standard system directories. By using these methods, the paths will be correct whether your app is sandboxed or not:
The URLsForDirectory:inDomains: method of the NSFileManager class returns a directory’s location packaged in an NSURL object. The directory to search for is an NSSearchPathDirectory constant. These constants provide URLs for the user’s home directory, as well as most of the standard directories.
The NSSearchPathForDirectoriesInDomains function behaves like the URLsForDirectory:inDomains: method but returns the directory’s location as a string-based path. You should use the URLsForDirectory:inDomains: method instead.
The NSHomeDirectory function returns the path to either the user’s or app’s home directory. (Which home directory is returned depends on the platform and whether the app is in a sandbox.) When an app is sandboxed the home directory points to the app’s sandbox, otherwise it points to the User’s home directory on the file system. If constructing a file to a subdirectory of a user’s home directory, you should instead consider using the URLsForDirectory:inDomains: method instead.
You can use the URL or path-based string you receive from the preceding routines to build new objects with the locations of the files you want. Both the NSURL and NSString classes provide path-related methods for adding and removing path components and making changes to the path in general. Listing 2-1 shows an example that searches for the standard Application Support directory and creates a new URL for a directory containing the app’s data files.
You cannot do it this way. Firstly it will break the code signature and secondly it's time consuming and error prone.
The correct approach is to not use the complete path in your code and instead use methods like NSSearchPathForDirectoriesInDomains to get the Documents folder, or whatever directory you want to use.
I need help getting access to the documents directory using only C on iOS.
I have my .c file looking for a specific file in the application bundle. I have no problem accessing this file. It looks like this: fopen("filename",
Unfortunately, if I want to move that file to the documents directory, appending "/Documents/filename" doesn't work.
I know how to access the file using an objective-c class, easily, using filesystemrepresentation. But I don't know how to do it only in C. Any help would be greatly appreciated!
Thanks!
Fopen defaults to the directory that the executable file is in, ".app/" - on iOS.
I was able to get to the documents directory by making a char of the Current Working Directory and then removing the last couple characters of the char to get out of the ".app/" bundle and then appending the Documents path to the end of it.