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Sunday, April 27, 2008

How File Processing is done in PHP?

In the previous post’s (Designing a Simple Order Form Application in PHP) example we implemented the file I/O for storing order information without discussing about it.

For those of you who were eager to know more about PHP File I/O read along, this post has it.

File processing requires the following steps:

  1. Opening a file
  2. Doing the operation
  3. Closing the file

Opening a file

First of all we have to open the file before any operation (reading/writing) can be done.

If you remember the previous post Designing a Simple Order Form Application in PHP, we had this line

//open file
$fp=fopen("orders.txt","a");

There we’re opening a file named “orders.txt” in the “append” file mode. File modes tell PHP what we want to do with the file.

Some of the commonly used files modes along with what they mean is listed below:

r For reading only, reading begins from the start of the file
r+ Reading and writing, beginning from the start of the file
w For writing only. Creates the file if it doesn’t exist. Deletes existing content if it exists.
w+ For writing and writing. Creates the file if it doesn’t exist. Deletes existing content if it exists.
a For appending (writing) beginning from the end of the existing data. Creates the file if it doesn’t exist.
a+ For appending (writing) and reading beginning from the end of the existing data. Creates the file if it doesn’t exist.

Doing the operation

Once the file is opened, we can any operation we want on it (of course those which are supported for that file mode).

In the previous post Designing a Simple Order Form Application in PHP, we used

//write the data to the opened file
fputs($fp,$data);

Here first argument is the file resource pointer and second is the string to be written to that file (pointed to by $fp).

fgets () is another function, it is used to read back information from file. It has the following form:

$data=fgets($fp,999);

It reads one line at a time marked by “\n” which here gets stored in the variable $data.

One line can also be when it encounters and EOF (End Of File) or when the line has length greater than the maximum length (999) to be read.

Besides these functions that operate on a file, there are many others but we won’t be discussing any more of them here.

Closing the file

after all the operations have been done we need to close the file. It is done like below:

//close the file
fclose($fp);

$fp is a file resource that needs to be closed.

It tells PHP and the Operating System that we’ve performed the operations we needed and it’s safe to close our link from that file.

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