Opening a file in PHP

When you open a file in PHP one of the first things you have to think about is what mode do you wish to open the file, Do you want to create a new file, Do you wish to open an existing file and add more data or do you wish to read data from an existing file. Some of the most common modes are displayed below.

Modes
"r" opens a file for reading only, the file pointer is at the beginning of the file
"r+" opens a file for reading/writing, file pointer is at the beginning of the file
"w" opens and clears file for writing only, if file does not exist it is created
"w+" Write/Read opens and clears the contents of the file, if file does not exist it is created
"a" append, Opens and writes to the end of the file or creates a new file if it does not exist
"a+" is Read/Append mode, writes to the end of the file
"x" will create a new file but it will return an error if the file already exists
"x+" Read/Write will create a new file but it will return an error if the file already exists

Lets look at some examples

Firstly we wish to open a file called myfile.txt for reading.

$file = fopen("myfile.txt","r") or die("Cannot open the file");
$fclose($file);

Our second example we will write to an existing file called testfile.txt

$file = fopen("testfile.txt","w") or die("Cannot open the file");
$fclose($file);

As you can see there are different ways to open files and whichever way you choose is dependent on what you wish to do with your script. An important thing to remember is if you already have data in a file and wish to keep it use the "a" or "a+" mode, a common gotcha is to clear the existing data by using the wrong mode.

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PHP On The Fly
How to Implement CAPTCHA With PHP and GD

So, you have a submission form on your website and need to prevent spam by auto-submitters. The most common way to do this is to implement CAPTCHA - an image with a randomly generated string (quote from Wikipedia, free online enciclopedia: “A CAPTCHA is a type of challenge-response test used in computing to determine whether the user is human. "CAPTCHA" is an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart", trademarked by Carnegie Mellon University.”)

Simple, quick and efficient PHP solution for implement CAPTCHA:

the advantage of this solution: it is easy to read symbols by human and automated captcha processor software, but hard to process the image by computer because common CAPTCHA processors can't understand which one of the outputted symbols it must ignore!

obviously you need PHP engine enabled for your webserver, for execute PHP scripts, and GD (PHP graphics library) for generate the image. Webserver, PHP and GD versions are no matter, the solution below is tested for Apache(Windows and Unix), IIS(Windows), PHP-4, PHP-5, GD, GD2

1) Make a PHP script (separate file captcha.php) which will generate the CAPTCHA image:
[?php
session_start();
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");
function _generateRandom($length=6){
$_rand_src = array(
array(48,57) //digits
, array(97,122) //lowercase chars
// , array(65,90) //uppercase chars
);
srand ((double) microtime() * 1000000);
$random_string = "";
for($i=0;$i<$length;$i++){
$i1=rand(0,sizeof($_rand_src)-1);
$random_string .= chr(rand($_rand_src[$i1][0],$_rand_src[$i1][1]));
}
return $random_string;
}
$im = @imagecreatefromjpeg("captcha.jpg");
$rand = _generateRandom(3);
$_SESSION['captcha'] = $rand;
ImageString($im, 5, 2, 2, $rand[0]." ".$rand[1]." ".$rand[2]." ", ImageColorAllocate ($im, 0, 0, 0));
$rand = _generateRandom(3);
ImageString($im, 5, 2, 2, " ".$rand[0]." ".$rand[1]." ".$rand[2], ImageColorAllocate ($im, 255, 0, 0));
Header ('Content-type: image/jpeg');
imagejpeg($im,NULL,100);
ImageDestroy($im);
?]

2) Add the following line at the top of the page where you need to implement the CAPTCHA (there should not be any output before this line, except you use php functions ob_start() and ob_end_flush() to turn on output buffering):
[?php session_start(); ?]

3) Add the following line for check is CAPTCHA entered by visitor valid, before the line where you will proceed submitted message:
[?php if($_SESSION["captcha"]==$_POST["captcha"])
{
//CAPTHCA is valid; proceed the message: save to database, send by e-mail ...
echo 'CAPTHCA is valid; proceed the message';
}
else {

echo 'CAPTHCA is not valid; ignore submission'; }?]

4) Finaly add the CAPTCHA to the form:
[img src="captcha.php" alt="captcha image"][input type="text" name="captcha" size="3" maxlength="3"]

P.S.
notice:
- the tags "[?" and "?]" in code samples above should be replaced to the "", you may download original article and code sample here: free download php captcha demo

- requirements: a webserver (windows or linux no matter) with PHP engine, with GD (graphic library) support, you may check your php settings with phpinfo() function

- you need some blank jpg image for use it as background for CAPTCHA string

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