(PHP 5, PHP 7, PHP 8)
variant_add — "Adds" two variant values together and returns the result
Adds left to right using
the following rules (taken from the MSDN library), which correspond to
those of Visual Basic:
| 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 |
leftThe left operand.
rightThe 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()。
Returns the result.
Throws a com_exception on failure.