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在过去如果我们调用一个用户定义的函数时，提供的参数不足，那么将会产生一个警告(warning)。 现在，这个警告被提升为一个错误异常(Error exception)。这个变更仅对用户定义的函数生效， 并不包含内置函数。例如：
<?php
function test($param){}
test();
以上例程的输出类似于：
Fatal error: Uncaught ArgumentCountError: Too few arguments to function test(), 0 passed in %s on line %d and exactly 1 expected in %s:%d
Dynamic calls for certain functions have been forbidden (in the form of
$func() or array_map('extract', ...),
etc). These functions either inspect or modify another scope, and present
with them ambiguous and unreliable behavior. The functions are as follows:
<?php
(function () {
$func = 'func_num_args';
$func();
})();
以上例程会输出：
Warning: Cannot call func_num_args() dynamically in %s on line %d
The following names cannot be used to name classes, interfaces, or traits:
Integer operations and conversions on numerical strings now respect
scientific notation. This also includes the (int) cast
operation, and the following functions: intval() (where
the base is 10), settype(), decbin(),
decoct(), and dechex().
mt_rand() will now default to using the fixed version of
the Mersenne Twister algorithm. If deterministic output from
mt_rand() was relied upon, then
MT_RAND_PHP can be used as optional second parameter
to mt_srand() to preserve the old (incorrect)
implementation.
rand() and srand() have now been made aliases to mt_rand() and mt_srand(), respectively. This means that the output for the following functions have changed: rand(), shuffle(), str_shuffle(), and array_rand().
The ASCII delete control character (0x7F) can no longer
be used in identifiers that are not quoted.
error_log changes with syslog
value
If the error_log ini setting is set to
syslog, the PHP error levels are mapped to the syslog
error levels. This brings finer differentiation in the error logs in
contrary to the previous approach where all the errors are logged with the
notice level only.
对于在执行构造方法时抛出异常的对象，现在析构方法绝不会被调用。在先前的版本中，这个行为取决于对象是否在构造方法以外的地方呗引用（例如一个错误堆栈回溯）
call_user_func() 现在在调用一个以引用作为参数的函数时将始终产生一个警告。先前这取决于这个调用行为是否完全符合条件。
此外， call_user_func() 和 call_user_func_array() 在这种情况下将不再中断函数调用。现在会出现一个包含"expected reference"的警告信息，但函数调用将正常进行。
对字符串使用一个空索引操作符（例如$str[] = $x）将会抛出一个致命错误，
而不是静默地将其转为一个数组。
下列ini配置项已经被移除：
session.entropy_file
session.entropy_length
session.hash_function
session.hash_bits_per_character
The order of the elements in an array has changed when those elements have been automatically created by referencing them in a by reference assignment. For example:
<?php
$array = [];
$array["a"] =& $array["b"];
$array["b"] = 1;
var_dump($array);
?>
以上例程在 PHP 7.0 中的输出：
array(2) {
["a"]=>
&int(1)
["b"]=>
&int(1)
}
以上例程在 PHP 7.1 中的输出：
array(2) {
["b"]=>
&int(1)
["a"]=>
&int(1)
}
The internal sorting algorithm has been improved, what may result in different sort order of elements, which compare as equal, than before.
注意:
Don't rely on the order of elements which compare as equal; it might change anytime.
The error message for E_RECOVERABLE errors has been changed from "Catchable fatal error" to "Recoverable fatal error".
The allowed_classes element of the $options parameter of
unserialize() is now strictly typed, i.e. if anything
other than an array or a bool is given,
unserialize() returns false and issues an E_WARNING.
DateTime and DateTimeImmutable
now properly incorporate microseconds when constructed from the current time,
either explicitly or with a relative string (e.g. "first day of next
month"). This means that naive comparisons of two newly created
instances will now more likely return false instead of true:
<?php
new DateTime() == new DateTime();
?>
In the Date extension, invalid serialization data for DateTime or DatePeriod classes, or timezone initialization failure from serialized data, will now throw an Error exception from the __wakeup() or __set_state() methods, instead of resulting in a fatal error.
In the DBA extension, data modification functions (such as dba_insert()) will now throw an Error exception instead of triggering a catchable fatal error if the key does not contain exactly two elements.
In the DOM extension, invalid schema or RelaxNG validation contexts will now throw an Error exception instead of resulting in a fatal error. Similarly, attempting to register a node class that does not extend the appropriate base class, or attempting to read an invalid property or write to a readonly property, will also now throw an Error exception.
In the IMAP extension, email addresses longer than 16385 bytes will throw an Error exception instead of resulting in a fatal error.
In the Intl extension, failing to call the parent constructor in a class extending Collator before invoking the parent methods will now throw an Error instead of resulting in a recoverable fatal error. Also, cloning a Transliterator object will now throw an Error exception on failure to clone the internal transliterator instead of resulting in a fatal error.
In the LDAP extension, providing an unknown modification type to ldap_batch_modify() will now throw an Error exception instead of resulting in a fatal error.
In the mbstring extension, the mb_ereg() and mb_eregi() functions will now throw a ParseError exception if an invalid PHP expression is provided and the 'e' option is used.
In the Mcrypt extension, the mcrypt_encrypt() and mcrypt_decrypt() will now throw an Error exception instead of resulting in a fatal error if mcrypt cannot be initialized.
In the mysqli extension, attempting to read an invalid property or write to a readonly property will now throw an Error exception instead of resulting in a fatal error.
In the Reflection extension, failing to retrieve a reflection object or retrieve an object property will now throw an Error exception instead of resulting in a fatal error.
In the Session extension, custom session handlers that do not return strings for session IDs will now throw an Error exception instead of resulting in a fatal error when a function is called that must generate a session ID.
In the SimpleXML extension, creating an unnamed or duplicate attribute will now throw an Error exception instead of resulting in a fatal error.
In the SPL extension, attempting to clone an SplDirectory object will now throw an Error exception instead of resulting in a fatal error. Similarly, calling ArrayIterator::append() when iterating over an object will also now throw an Error exception.
In the standard extension, the assert() function, when provided with a string argument as its first parameter, will now throw a ParseError exception instead of resulting in a catchable fatal error if the PHP code is invalid. Similarly, calling forward_static_call() outside of a class scope will now throw an Error exception.
In the Tidy extension, creating a tidyNode manually will now throw an Error exception instead of resulting in a fatal error.
In the WDDX extension, a circular reference when serializing will now throw an Error exception instead of resulting in a fatal error.
In the XML-RPC extension, a circular reference when serializing will now throw an instance of Error exception instead of resulting in a fatal error.
In the Zip extension, the ZipArchive::addGlob() method will now throw an Error exception instead of resulting in a fatal error if glob support is not available.
Variables bound to a closure via
the use construct cannot use the same name as any
superglobals, $this, or any parameter. For
example, all of these function definition will result in a fatal error:
<?php
$f = function () use ($_SERVER) {};
$f = function () use ($this) {};
$f = function ($param) use ($param) {};
long2ip() now expects an int instead of a string.
The serialize_precision ini setting now controls the
serialization precision when encoding floats.
Decoding an empty key now results in an empty property name, rather than
_empty_ as a property name.
<?php
var_dump(json_decode(json_encode(['' => 1])));
以上例程的输出类似于：
object(stdClass)#1 (1) {
[""]=>
int(1)
}
When supplying the JSON_UNESCAPED_UNICODE flag to
json_encode(), the sequences U+2028 and U+2029 are now
escaped.
The third parameter to the mb_ereg() and
mb_eregi() functions (regs) will now be
set to an empty array if nothing was matched. Formerly, the parameter would
not have been modified.
The sslv2 stream has now been dropped in OpenSSL.
Return statements without argument in functions which declare a return type
now trigger E_COMPILE_ERROR (unless the return type is
declared as void), even if the return statement would never be
reached.
