尽管大部分现有的 PHP 5 代码不需要任何改变就可以正常运行，但请注意一些不向后兼容的变更：
FALSE 。 调用 set_magic_quotes_runtime() 将产生一个 E_CORE_ERROR 级别的错误。
E_WARNING 错误。
E_WARNING 错误。偏移量类型是布尔和 null 则产生一条 E_NOTICE 错误。 数字字符串（比如 $a['2'] ）仍像以前一样运行。注意像类似 '12.3' 和 '5 foobar' 这样的偏移量将被视为非数字并产生一条 E_WARNING 错误，但因为向后兼容的原因它们会被分别转换成 12 和 5 。
注意：下列代码返回不同的结果。
$str='abc';var_dump(isset($str['x'])); // 在 PHP 5.4 或更新版本返回 false，但在 PHP 5.3 或更低版本返回 true
E_NOTICE 级别的错误，但返回的结果仍是字符串 "Array" 。
NULL 、FALSE 、或 一个空字符串被添加成一个对象的属性时将发出一条 E_WARNING 级别的错误，而不是 E_STRICT 。
FALSE 。
E_STRICT 错误。
下列关键字现在被 保留 ，且不能用于函数名或类名。
下列函数已从 PHP 中移除：
Be careful, in php 5.4. \e in string mean the escape character !
So you will have error for windows path:
$a = "c:\extend\toto.txt";
AND for date function:
echo date ("\t\h\e dmy");
you will have an escape character in your source instead "e"
The workaround I found is simple quote:
echo date ('\t\h\e dmy');
If you have content that is not 100% UTF-8 then TAKE NOTE:
Starting in PHP 5.4 htmlspecialchars() and htmlentities() assume CHARSET=gb2312 by default AND WILL RETURN BLANK IF YOUR INPUT IS NOT VALID UTF-8.
So if you have a lot of function calls that look like this:
<?php
echo htmlspecialchars($input);
// or
echo htmlentities($input);
?>
i.e. no charset and no flags -- and $input is ISO-8859 (or anything else apart from 7-bit ASCII or UTF-8) -- then PHP 5.4 and 5.5 will return an empty string, and you will be surprised and probably unhappy.
This is apparently a feature, not a bug.
'<?if'... worked in 5.3 as equivalent of '<?php if'... In 5.4 it's converted to '<!--?if'...
It seems that starting of PHP 5.4 you can not override class method with different signature.
Example:
<?php
class A
{
public function doSomething($a, $b)
{
}
}
class B extends A
{
public function doSomething($c)
{
}
}
?>
PHP Strict standards: Declaration of B::doSomething() should be compatible with A::doSomething(B $a) in Command line code on line 1
There should be samples given here. There are many ways to do such coversion:
Converting an array to a string will now generate an E_NOTICE level error, but the result of the cast will still be the string "Array".
It's not a PHP version incompatibility itself, but it's important to know that Microsoft dropped the php_mssql.dll support for the "mssql_" funcitions since this version.
To connect to a MSSQL database since 5.4, one good alternative are the PDO drivers.
Missing some chars like german umlauts after use of htmlspecialchars? That's because the third param encoding has changed it's default value in PHP 5.4 from ISO-8859-1 to UTF-8.
Possible solution #1:
Change your code from this ...
<?php htmlspecialchars( '??ü' ); ?>
... to this:
<?php htmlspecialchars ( '??ü' , ENT_COMPAT | ENT_HTML401 , 'ISO-8859-1' ); ?>
Possible solution #2:
Create a wrapper function and replace htmlspecialchars( to i.e. isohtmlspecialchars( with your IDE/editor/shell...
Example of a wrapper function:
<?php
function isohtmlspecialchars( $str ){
return htmlspecialchars ( $str , ENT_COMPAT | ENT_HTML401 , 'ISO-8859-1' );
}
?>