PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Opening a File
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The form field for the shipping address is called address.This gives you a variable you
can access as $_REQUEST[‘address’] or $_POST[‘address’] or $_GET[‘address’],
depending on the form submission METHOD. (See Chapter 1,“PHP Crash Course,” for
details.)
In this chapter, you write each order that comes in to the same file.Then you construct
a web interface for Bob’s staff to view the orders that have been received.
Processing Files
Writing data to a file requires three steps:
1. Open the file. If the file doesn’t already exist, you need to create it.
2. Write the data to the file.
3. Close the file.
Similarly, reading data from a file takes three steps:
1. Open the file. If you cannot open the file (for example, if it doesn’t exist), you
need to recognize this and exit gracefully.
2. Read data from the file.
3. Close the file.
When you want to read data from a file, you have many choices about how much of the
file to read at a time.We describe some common choices in detail. For now, we start at
the beginning by opening a file.
Opening a File
To open a file in PHP, you use the fopen() function.When you open the file, you need
to specify how you intend to use it.This is known as the file mode.
Choosing File Modes
The operating system on the server needs to know what you want to do with a file that
you are opening. It needs to know whether the file can be opened by another script
while you have it open and whether you (or the script owner) have permission to use it
in that way. Essentially, file modes give the operating system a mechanism to determine
how to handle access requests from other people or scripts and a method to check that
you have access and permission to a particular file.
You need to make three choices when opening a file:
1. You might want to open a file for reading only, for writing only, or for both reading
and writing.
2. If writing to a file, you might want to overwrite any existing contents of a file or
append new data to the end of the file.You also might like to terminate your program
gracefully instead of overwriting a file if the file already exists.