Text files can be extremely useful for storing various kinds of data. They are not quite as flexible as real databases, but text files typically don't require as much memory. Moreover, text files are a plain and simple format that works on most systems.
Open the text file
We use the
fopen function to open a text file. The syntax is as follows:| fopen(filename, mode) |
|---|
- filename
- Name of the file to be opened.
- mode
- Mode can be set to "r" (reading), "w" (writing) or "a" (appending). In this lesson, we will only read from a file and, therefore, use "r". In the next lesson, we will learn to write and append text to a file.
First, let's try to open unitednations.txt:
Example 1: Read a line from the text file
With the functionfgets, we can read a line from the text file. This method reads until the first line break (but not including the line break).show example
Example 2: Read all lines from the text file
show example
In the example, we loop through all the lines and use the function
feof
(for end-of-file) to check if you are at the end of the file. If this
is not the case ("!" - see lesson 6), the line is written.Instead of looping through all the lines, we could have achieved the same result with the function documentationfread. If you work with very large text files with thousands of lines, be aware that the documentationfread function uses more resources than the
fgets function. For smaller files, it makes very little difference.Example 3: A simple link directory
As mentioned at the beginning of this lesson, text files can be excellent for data storage. This is illustrated in the next example where we create a simple link directory from the contents of the text file unitednations.txt.The file is systematically written with the name of the program, then a comma, and then the domain. As you can probably imagine, more information could easily be stored in this comma-separated data file.
To get the information in each line, we use an array. See Lesson 8 for more information on arrays.
show example
Quite handy, right? In principle, you could now just expand the text file with hundreds of links or perhaps expand your directory to also include address information.
In the next lesson, we will look at how to write to a text file.
