PHP Manual: variant

Description

mixed variant_sub ( mixed left, mixed right )

Subtracts right from left using the following rules:

Table 1. Variant Subtraction Rules

If	Then
Both expressions are of the string type	Subtraction
One expression is a string type and the other a character	Subtraction
One expression is numeric and the other is a string	Subtraction.
Both expressions are numeric	Subtraction
Either expression is NULL	NULL is returned
Both expressions are empty	Empty string is returned

See also variant_add().

Note: As with all the variant arithmetic functions, the parameters for this function can be either a PHP native type (integer, string, floating point, boolean or NULL), or an instance of a COM, VARIANT or DOTNET class. PHP native types will be converted to variants using the same rules as found in the constructor for the VARIANT class. COM and DOTNET objects will have the value of their default property taken and used as the variant value.
The variant arithmetic functions are wrappers around the similarly named functions in the COM library; for more information on these functions, consult the MSDN library. The PHP functions are named slightly differently; for example variant_add() in PHP corresponds to VarAdd() in the MSDN documentation.