I have seen uses of @ in front of certain functions, like the following:
$fileHandle = @fopen($fileName, $writeAttributes);
What is the use of this symbol?
php
operators
error-suppression
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Answers
2
@ suppresses errors, warnings and notices.
You can use it for good purpose if you complement it with a custom error handler or with due check of $php_errormsg variable so you can handle errors properly.
In my experience, this proper usage is not seen very much and is instead used a lot in the bad way, just to hide errors without acting on them.
More info at http://www.php.net/manual/en/language.operators.errorcontrol.php
Monday, October 10, 2022
3
I would suppress the error and handle it. Otherwise you may have a TOCTOU issue (Time-of-check, time-of-use. For example a file may get deleted after file_exists returns true, but before fopen).
But I wouldn't just suppress errors to make them go away. These better be visible.
Thursday, August 18, 2022
3
@ has been around since the days of @import in CSS1, although it's arguably becoming increasingly common in the recent @media (CSS2, CSS3) and @font-face (CSS3) constructs. The @ syntax itself, though, as I mentioned, is not new.
These are all known in CSS as at-rules. They're special instructions for the browser, not directly related to styling of (X)HTML/XML elements in Web documents using rules and properties, although they do play important roles in controlling how styles are applied.
Some code examples:
/* Import another stylesheet from within a stylesheet */
@import url(style2.css);
/* Apply this style only for printing */
@media print {
body {
color: #000;
background: #fff;
}
}
/* Embed a custom web font */
@font-face {
font-family: 'DejaVu Sans';
src: local('DejaVu Sans Regular'), url(/fonts/DejaVuSans.ttf);
}
@font-facerules define custom fonts for use in your designs that aren't always available on all computers, so a browser downloads a font from the server and sets text in that custom font as if the user's computer had the font.@mediarules, in conjunction with media queries (formerly only media types), control which styles are applied and which aren't based on what media the page is being displayed in. In my code example, only when printing a document should all text be set in black against a white (the paper) background. You can use media queries to filter out print media, mobile devices and so on, and style pages differently for those.
At-rules have no relation to selectors whatsoever. Because of their varying nature, different at-rules are defined in different ways across numerous different modules. More examples include:
- Conditional rules
- Keyframe animations
- Paged media
(this list is far from exhaustive)
You can find another non-exhaustive list at MDN.
Thursday, September 29, 2022
3
UPDATE
G forces the pattern to only return matches that are part of a continuous chain of matches. From the first match each subsequent match must be preceded by a match. If you break the chain the matches end.
<?php
$pattern = '#(match),#';
$subject = "match,match,match,match,not-match,match";
preg_match_all( $pattern, $subject, $matches );
//Will output match 5 times because it skips over not-match
foreach ( $matches[1] as $match ) {
echo $match . '<br />';
}
echo '<br />';
$pattern = '#(Gmatch),#';
$subject = "match,match,match,match,not-match,match";
preg_match_all( $pattern, $subject, $matches );
//Will only output match 4 times because at not-match the chain is broken
foreach ( $matches[1] as $match ) {
echo $match . '<br />';
}
?>
This is straight from the docs
The fourth use of backslash is for certain simple assertions. An assertion specifies a condition that has to be met at a particular point in a match, without consuming any characters from the subject string. The use of subpatterns for more complicated assertions is described below. The backslashed assertions are
G
first matching position in subject
The G assertion is true only when the current matching position is at the start point of the match, as specified by the offset argument of preg_match(). It differs from A when the value of offset is non-zero.
http://www.php.net/manual/en/regexp.reference.escape.php
You will have to scroll down that page a bit but there it is.
There is a really good example in ruby but it is the same in php.
How the Anchor z and G works in Ruby?
Monday, November 28, 2022
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It suppresses error messages — see Error Control Operators in the PHP manual.