Re absolute fastest way to save and read data from text file or binary file
Common Lisp provides a general solution to the problem of how to ensure that certain code always runs: You obtain a stream from which you can read a file's contents with the OPEN function. Accessing Other Directories Programmatically The earlier directory and file examples accessed the Documents directory. READ-BYTElike the character-reading functions, also accepts optional arguments to specify whether it should signal an error if called at the end of the file and what value to return if not. Simply add the NuGet package to your application's project:.
This screenshot shows how these appear in iTunes: The home directory is a unique location in the file system where your application and all its data are stored. You cannot choose or change the location of the home directory for your application; however iOS and Xamarin. This example will display the contents of a text file in the Application Output window.
It takes a pathname designator and returns an equivalent pathname object. However, despite the familiar classes and methods, iOS implements some restrictions on the files that can be created or accessed and also provides special features for certain directories. In the pathname portability library I'll discuss in the next chapter, you'll write a function called pathname-as-directory that converts a pathname to directory form. Simply add the NuGet package to your application's project:
To restrict the list to filenames that contain a particular substring, use an anonymous function inside filter — something like this:. For example, the tmp directory might be used to store temporary files that are downloaded for display to the user such as Twitter avatars or email attachmentsbut which could be deleted once they've been viewed and downloaded again if they are required in the future. However, if you want your programs to be portable, you probably don't want to make pathnames completely from scratch: Otherwise, it returns NIL.
And because s-expressions were designed to be human editable, it's also a fine format for things like configuration files. This screenshot shows the directory structure in a Finder window: And if you use the DataFrames package, there's also a readtable specifically designed to read data into a table. When opening a file for output, OPEN assumes the file shouldn't already exist and will signal an error if it does. Similarly, the standard function for listing files in the file system, DIRECTORYworks fine for simple cases, but the differences between implementations make it tricky to use portably.
Users can only access the top-level items in this directory via iTunes. This means if your filename casing differs between the file itself and the references to it in code, your code might still work in the simulator but that it would fail on a real device. As long as sensitive files remain hidden, these files will not be exposed and potentially moved, modified, or deleted by iTunes if file sharing is enabled in a future version.
Views Read Edit View history. Accessing Other Directories Programmatically The earlier directory and file examples accessed the Documents directory. It takes a pathname designator and ensures that all the elements of the directory component exist and are directories, creating them as necessary. Right-click on this icon and choose View Package Contents to browse the contents of the Application Bundle directory.
When called with just a stream, this function returns the current position in the file--the number of elements that have been read from or written to the stream. If you really have to know the number of characters in a file, you have to bite the bullet and write something like this: Another reason not to make pathnames completely from scratch is that different implementations use the pathname components slightly differently. So, although nothing should be written to the root directory, in iOS 7 and earlier creates a number of directories within the application root directory that are available for use. Only store user-generated data, or data that cannot otherwise be re-created, in the Documents directory which is backed-up.