Standard variable expressions
Important
The modern print platform is Windows' preferred means of communicating with printers. We recommend that you use Microsoft's IPP inbox class driver, along with Print Support Apps (PSA), to customize the print experience in Windows 10 and 11 for printer device development.
For more information, see Modern print platform and the Print support app design guide.
When you specify arguments in a command string, you can specify the argument value as an expression. This expression can perform operations using the current values of the standard variables. Each standard variable expression within a command string is delimited by braces ( {, } ).
A standard variable expression can consist of a combination of the following components:
Zero, one, or more standard variables
Integer numeric values
Expression operators
A standard variable expression can't contain embedded macro references.
The expression operators are included in the following table.
| Operator | Definitions |
|---|---|
| Val1+Val2 | Addition |
| Val1-Val2 | Subtraction |
| Val1/Val2 | Division |
| Val1*Val2 | Multiplication |
| Val1MODVal2 | Modulus. Value is the remainder of dividing Val1 by Val2. |
| max ( Val1 , Val2 ) | Maximum. Value is the maximum of Val1 and Val2. |
| max_repeat ( Val1 ) | See the Using max_repeat section. |
| min ( Val1 , Val2 ) | Minimum. Value is the minimum of Val1 and Val2. |
| ( ) | Precedence operators. If not used, C language precedence is used. |
Standard variable expressions don't modify the values assigned to the standard variables. The calculated value is placed in the escape sequence, using the format specified by the command string argument type specifier.
Using max_repeat
The use of max_repeat is best explained with an example. Suppose a GPD file contains the following entry:
*Command:CmdXMoveRelRight{*Cmd:"<1B>["%d[0,9600]{max_repeat((DestXRel/4))}"a"}
This command contains a single argument, of type %d. It also contains an argument range specification. Whenever Unidrv sends this command to the printer, it first calculates DestXRel/4 and determines if it is within the specified range. If the calculated value is greater than 9600, Unidrv sends the command repeatedly, with a maximum value of 9600, until the specified value is sent. Thus if DestXRel/4 equals 20,000, Unidrv sends the following commands:
<1B>[9600
<1B>[9600
<1B>[800
The max_repeat operator can be used only if the following conditions are met:
A command string includes only a single argument.
The argument includes a range specification.