ITEC 325 2014spring ibarland

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lect05-php-output
printing in php
error-reporting; default-print

• Running your php programs:
  1. First run them directly from the command-line: php myfile.php. If you have syntax error, it will give you a line-number
     (as opposed to running via the web, which will just quit w/o any output).
  2. Start your file with the following:

     <?php error_reporting(E_ALL|E_STRICT); ini_set('display_errors', 'stderr'); ini_set('display_startup_errors', true); ?>

     Be aware though:
     • You want to put these right near the start of your file, of course. It doesn't do good to turn on error-reporting on line 20, if you first have an error on line 10!
     • A Gotcha: even if the first line of your program turns on error-reporting, your script might crash w/o notice (or line-number)?!

       Reason: Before the first line of your program is run, php parses your entire file. If you have a missing semicolon on line 20, then line 1 will never even be run.

       Solutions:

       1. Run from the command-line, before trying to run it via the web¹.
       2. Make a shell file which simply calls error_report, and then require the file with your real code! In practice, this is kinda clunky.
       3. Set these configuration options in .htaccess, Apache's per-directory configuration file.
       In practice, I do both (a) and (c).

     • Calling ini_set has no effect on the current php process — it will only effect any files you include. (But that's enough reason to do it.)
     • For php 5.4, E_ALL already subsumes E_STRICT. However

       php.radford.edu

       is running php 5.3.
     • Even if your program crashes halfway through, there may or may not be output depending on whether the output was being buffered. (See flush, to manually flush the output-buffer.)
• (optional) PHP Error Types

  Notice

  Non-fatal error that may or may not be indicative of a problem.
  E.g., Referring to a variable that has no value.

  Warning

  Nonfatal error that is most likely problematic.
  E.g., Misusing a function.

  Parse error

  Fatal error caused by a syntactic mistake.
  E.g., Omission of a semicolon or an imbalance of quotation marks, braces, or parentheses.

  Error

  A general fatal error.
  E.g., out of memory.

• (optional) Error Reporting Constants
  • E_NOTICE
  • E_WARNING
  • E_PARSE
  • E_ERROR
  • E_ALL
  • E_STRICT (the only one not supported by E_ALL; warns of things which might not be future compatible, etc.

  As we saw, we can combine values (to use as an argument to error_report( $level )) by bitwise-ORing (“|”) various constants. legal error flags; It is recommended to use error_report(E_ALL|E_STRICT).

  See also various error functions.

• Printing from php:

  We can shorten silly-page-php.txt to silly-page-v2-php.txt.
  (Self-quiz: Why can't I do a show-source of silly-page.php, to see the php code?)

  Compare echoing “\n” vs “<br />”.

• php echo vs. print: The latter is a function (takes one input, and returns a boolean). You'd think I prefer print, because it conceivably composes with other functions (albeit after yielding a side-effect). But in practice I find I use echo: I prefer using (any number of) , to echo multiple items (rather than . to string-append), and I never (want to) use the result from a side-effecting function.
• Looking at silly-page-v2-php.txt: examine the use of single-quote vs. double-quote. Let's evaluate:

  "hello" . 17 'hello' "he'llo" 'he"llo' $myName = "Ian" "hello, $myName.\nBye." 'hello, $myName.\nBye' strlen("hi\n") strlen('hi\n')

  Take-away: I recommend using " for your php strings; when you create strings containing html, that html will use ' for its attribute-values. This convention minimizes conflicts between php strings and html(javascript) values, and lets you use php's variable-substitution.

Note: Arguably, php, with all its flaws, owes its success entirely to that variable-substitution, and the convention that anything not inside a php processing-instruction should be literal output. (FWIW, a better way to blend code with large amoutns of literal-text-data is racket's “scribble” syntax: it nests better, and generalizes better.)

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©2013, Ian Barland, Radford University Last modified 2014.Jan.31 (Fri)

Please mail any suggestions (incl. typos, broken links) to ibarlandradford.edu