First, let’s see how you would take the contents of an NSString and put it into a file. When you write a string to a file, you need to specify which string encoding you are using. A string encoding describes how each character is stored as an array of bytes. ASCII is a string encoding that defines the letter ‘A’ as being stored as 01000001. In UTF-16, the letter ‘A’ is stored as 0000000001000001.

The Foundation framework supports about 20 different string encodings. UTF can handle an incredible collection of writing systems. It comes in two flavors: UTF-16, which uses two or more bytes for every character, and UTF-8, which uses one byte for the first 128 ASCII characters and two or more for other characters. For most purposes, UTF-8 is a good fit.

Create a new project: a Foundation Command Line Tool called Stringz. In main(), use methods from the NSString class to create a string and write it to the filesystem:

#​i​m​p​o​r​t​ ​<​F​o​u​n​d​a​t​i​o​n​/​F​o​u​n​d​a​t​i​o​n​.​h​>​

i​n​t​ ​m​a​i​n​ ​(​i​n​t​ ​a​r​g​c​,​ ​c​o​n​s​t​ ​c​h​a​r​ ​*​ ​a​r​g​v​[​]​)​ ​ ​ ​ ​{​
 ​ ​ ​ ​@​a​u​t​o​r​e​l​e​a​s​e​p​o​o​l​ ​{​

 ​ ​ ​ ​ ​ ​ ​ ​N​S​M​u​t​a​b​l​e​S​t​r​i​n​g​ ​*​s​t​r​ ​=​ ​[​[​N​S​M​u​t​a​b​l​e​S​t​r​i​n​g​ ​a​l​l​o​c​]​ ​i​n​i​t​]​;​
 ​ ​ ​ ​ ​ ​ ​ ​f​o​r​ ​(​i​n​t​ ​i​ ​=​ ​0​;​ ​i​ ​<​ ​1​0​;​ ​i​+​+​)​ ​{​
 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​[​s​t​r​ ​a​p​p​e​n​d​S​t​r​i​n​g​:​@​"​A​a​r​o​n​ ​i​s​ ​c​o​o​l​!​​n​"​]​;​
 ​ ​ ​ ​ ​ ​ ​ ​}​
 ​ ​ ​ ​ ​ ​ ​ ​[​s​t​r​ ​w​r​i​t​e​T​o​F​i​l​e​:​@​"​/​t​m​p​/​c​o​o​l​.​t​x​t​"​
 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​a​t​o​m​i​c​a​l​l​y​:​Y​E​S​
 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​e​n​c​o​d​i​n​g​:​N​S​U​T​F​8​S​t​r​i​n​g​E​n​c​o​d​i​n​g​
 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​e​r​r​o​r​:​N​U​L​L​]​;​
 ​ ​ ​ ​ ​ ​ ​ ​N​S​L​o​g​(​@​"​d​o​n​e​ ​w​r​i​t​i​n​g​ ​/​t​m​p​/​c​o​o​l​.​t​x​t​"​)​;​

 ​ ​ ​ ​}​
 ​ ​ ​ ​r​e​t​u​r​n​ ​0​;​
}​

This program will create a text file that you can read and edit in any text editor. The string /tmp/cool.txt is known as the file path. File paths can be absolute or relative: absolute paths start with a / that represents the top of the file system, whereas relative paths start at the working directory of the program. Relative paths do not start with a /. In Objective-C programming, you’ll find that we nearly always use absolute paths because we typically don’t know what the working directory of the program is.