参考——这个符号在 PHP 中是什么意思? [英] Reference — What does this symbol mean in PHP?

示例名称效果---------------------------------------------------------------------++$a Pre-increment 将 $a 增加 1，然后返回 $a.$a++ 后增量返回 $a，然后将 $a 加一.--$a Pre-decrement 将 $a 减一，然后返回 $a.$a-- 递减后返回 $a，然后将 $a 减一.

这些可以在变量之前或之后.

如果放在变量之前，则先对变量进行递增/递减操作，然后返回结果.如果放在变量之后，则变量先返回，然后进行递增/递减操作.

例如:

$apples = 10;for ($i = 0; $i <10; ++$i) {回声我有".$apples-- ." 苹果.我只吃了一个.\n";}

实例

在上面的例子中使用 ++$i，因为它更快.$i++ 会得到相同的结果.

预增量稍微快一点，因为它确实增加了变量，然后返回"了结果.后增量创建一个特殊变量，在那里复制第一个变量的值，只有在第一个变量被使用后，才用第二个变量替换它的值.

但是，您必须使用$apples--，因为首先您要显示当前的苹果数量，然后然后要从中减去一个.

您也可以在 PHP 中递增字母:

$i = "a";而 ($i < "c") {回声 $i++;}

一旦到达z，下一个是aa，依此类推.

<块引用>

请注意，字符变量可以递增但不能递减，即使如此，也仅支持纯 ASCII 字符(a-z 和 A-Z).

<小时>

堆栈溢出帖子:

了解增量

What is this?

This is a collection of questions that come up every now and then about syntax in PHP. This is also a Community Wiki, so everyone is invited to participate in maintaining this list.

Why is this?

It used to be hard to find questions about operators and other syntax tokens.¹
The main idea is to have links to existing questions on Stack Overflow, so it's easier for us to reference them, not to copy over content from the PHP Manual.

Note: Since January 2013, Stack Overflow does support special characters. Just surround the search terms by quotes, e.g. [php] "==" vs "==="

What should I do here?

If you have been pointed here by someone because you have asked such a question, please find the particular syntax below. The linked pages to the PHP manual along with the linked questions will likely answer your question then. If so, you are encouraged to upvote the answer. This list is not meant as a substitute for the help others provided.

The List

If your particular token is not listed below, you might find it in the List of Parser Tokens.

& Bitwise Operators or References

=& References

&= Bitwise Operators

&& Logical Operators

% Arithmetic Operators

!! Logical Operators

Double not (!!) operator in PHP

@ Error Control Operators

?: Ternary Operator

?? Null Coalesce Operator (since PHP 7)

C#'s null coalescing operator (??) in PHP

?string ?int ?array ?bool ?float Nullable return type declaration (since PHP 7.1)

: Alternative syntax for control structures, Ternary Operator, Return Type Declaration

:: Scope Resolution Operator

\ Namespaces

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^ Bitwise Operators

>> Bitwise Operators

What does >> mean in PHP?

<< Bitwise Operators

Strange print behaviour in PHP?

<<< Heredoc or Nowdoc

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The 3 different equals

== Comparison Operators

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Spaceship (three way comparison) operator

| Bitwise Operators

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What does this ~ operator mean here?

+ Arithmetic Operators, Array Operators

+ operator for array in PHP?

+= and -= Assignment Operators

++ and -- Incrementing/Decrementing Operators

.= Assignment Operators

. String Operators

, Function Arguments

Difference between period and comma when concatenating with echo versus return?

, Variable Declarations

What do commas mean in a variable declaration?

$$ Variable Variables

` Execution Operator

What are the backticks `` called?

<?= Short Open Tags

[] Arrays (short syntax since PHP 5.4)

<? Opening and Closing tags

Are PHP short tags acceptable to use?

... Argument unpacking (since PHP 5.6)

** Exponentiation (since PHP 5.6)

# One-line shell-style comment

Can I use hashes for comments in PHP?

?-> NullSafe Operator Calls (since PHP 8.0)

What does this symbol mean "?->" in php, within an object or null value

解决方案

Incrementing / Decrementing Operators

++ increment operator

-- decrement operator

Example    Name              Effect
---------------------------------------------------------------------
++$a       Pre-increment     Increments $a by one, then returns $a.
$a++       Post-increment    Returns $a, then increments $a by one.
--$a       Pre-decrement     Decrements $a by one, then returns $a.
$a--       Post-decrement    Returns $a, then decrements $a by one.

These can go before or after the variable.

If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.

For example:

$apples = 10;
for ($i = 0; $i < 10; ++$i) {
    echo 'I have ' . $apples-- . " apples. I just ate one.\n";
}

Live example

In the case above ++$i is used, since it is faster. $i++ would have the same results.

Pre-increment is a little bit faster because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.

However, you must use $apples--, since first, you want to display the current number of apples, and then you want to subtract one from it.

You can also increment letters in PHP:

$i = "a";
while ($i < "c") {
    echo $i++;
}

Once z is reached aa is next, and so on.

Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

Stack Overflow Posts:

Understanding Incrementing

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参考——这个符号在 PHP 中是什么意思? [英] Reference — What does this symbol mean in PHP?

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这是什么?

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我应该在这里做什么?

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Why is this?

What should I do here?

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相关文章

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