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Unit 9: Working with Forms
13. } Notes
14. $guess = $_POST[guess];
15. ?>
16. <html>
17. <head>
18. <title>Listing 8 Saving state with a hidden field</title>
19. </head>
20. <body>
21. <h1>
22. < ?php print $message ? >
23. </h1>
24. Guess number: < ?php print $num_tries? >
25. <form action=”< ?php print $_SERVER[PHP_SELF] ?>” method=”POST” >
26. Type your guess here:
27. <input type=”text” name=”guess” value=”< ?php print $guess? >”>
28. <input type=”hidden” name=”num_tries” value=”< ?php print $num_tries? >”>
29. </form>
30. </body>
31. </html>
The hidden field on line 28 is given the name “num_tries”. We also use PHP to write its value.
While we’re at it, we do the same for the “guess” field on line 27 so that the user can always
see his last guess. This technique is useful for scripts that parse user input. If we reject a form
submission for some reason, we can at least allow our user to edit his previous query.
Be sure that absolutely no output has been sent to the browser. The first time
content is sent to the browser, PHP sends out headers and it’s too late for
you to send your own. Any output from your document, even a line break
or a space outside of your script tags, causes headers to be sent. If you intend
to use the header() function in a script, you must make certain that nothing
precedes the PHP code that contains the function call. You should also check
any libraries that you might be using.
Listing 9 shows typical headers sent to the browser by PHP, beginning with line 3, in response
to the request in line.
9.6 Redirecting the User
Our simple script still has one major drawback. The form is rewritten whether or not the user
guesses correctly. The fact that the HTML is hard-coded makes it difficult to avoid writing the
entire page. We can, however, redirect the user to a congratulations page, thereby sidestepping
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