"Adds" two variant values together and returns the result

# variant_add

(PHP 5, PHP 7, PHP 8)

variant_add — "Adds" two variant values together and returns the result

### 说明

function variant_add(mixed `$left`, mixed `$right`): variant

Adds `left` to `right` using the following rules (taken from the MSDN library), which correspond to those of Visual Basic:

Variant Addition Rules
If | Then
--- | ---
Both expressions are of the string type | Concatenation
One expression is a string type and the other a character | Addition
One expression is numeric and the other is a string | Addition
Both expressions are numeric | Addition
Either expression is NULL | NULL is returned
Both expressions are empty | Integer subtype is returned

### 参数

`left`

  The left operand.

`right`

  The right operand.

> 注意: 对于所有变量运算函数，本函数的参数可以是 PHP 内置的类型（整数，字符串，浮点数，布尔型或者 `null`），或者是一个 COM，VARIANT 或者 DOTNET 类的实例。PHP 内置类型将会使用和构造variant类相同的规则转换成变量。COM 和 DOTNET 对象的值将会取其默认属性并被当成变量值使用。 变量运算函数是同名函数在 COM 库中的外包；有关此类函数的更多信息参见 MSDN 库。PHP 函数命名有少许区别，例如 PHP 中的 variant_add() 对应于 MSDN 文档中的 `VarAdd()`。

### 返回值

Returns the result.

### 错误／异常

Throws a com_exception on failure.

### 参见

- variant_sub() - Subtracts the value of the right variant from the left variant value

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