Makefile preprocessing

Article
02/17/2022

You can control the NMAKE session by using preprocessing directives and expressions. Preprocessing instructions can be placed in the makefile or in Tools.ini. Using directives, you can conditionally process your makefile, display error messages, include other makefiles, undefine a macro, and turn certain options on or off.

Makefile Preprocessing Directives

Preprocessing directives aren't case-sensitive. The initial exclamation point (!) must appear at the beginning of the line. Zero or more spaces or tabs can appear after the exclamation point, for indentation.

!CMDSWITCHES { +option | -option } ...

Turns each listed option on or off. Spaces or tabs must appear before the + or - operator. No spaces can appear between the operator and the option letters. Letters aren't case-sensitive and are specified without a slash (/). To turn on some options and turn off others, use separate specifications of !CMDSWITCHES.

Only /D, /I, /N, and /S can be used in a makefile. In Tools.ini, all options are allowed except /F, /HELP, /NOLOGO, /X, and /?. Changes specified in a description block don't take effect until the next description block. This directive updates MAKEFLAGS; changes are inherited during recursion if MAKEFLAGS is specified.
!ERROR text

Displays text in error U1050, then halts NMAKE, even if /K, /I, .IGNORE, !CMDSWITCHES, or the dash (-) command modifier is used. Spaces or tabs before text are ignored.
!MESSAGE text

Displays text to standard output. Spaces or tabs before text are ignored.
!INCLUDE [ < ] filename [ > ]

Reads filename as a makefile, then continues with the current makefile. NMAKE searches for filename first in the specified or current directory, then recursively through directories of any parent makefiles, then, if filename is enclosed by angle brackets (< >), in directories specified by the INCLUDE macro, which is initially set to the INCLUDE environment variable. Useful to pass .SUFFIXES settings, .PRECIOUS, and inference rules to recursive makefiles.
!IF constant_expression

Processes statements between !IF and the next !ELSE or !ENDIF if constant_expression evaluates to a nonzero value.
!IFDEF macro_name

Processes statements between !IFDEF and the next !ELSE or !ENDIF if macro_name is defined. A null macro is considered to be defined.
!IFNDEF macro_name

Processes statements between !IFNDEF and the next !ELSE or !ENDIF if macro_name isn't defined.
!ELSE [ IF constant_expression | IFDEF macro_name | IFNDEF macro_name ]

Processes statements between !ELSE and the next !ENDIF if the prior !IF, !IFDEF, or !IFNDEF statement evaluated to zero. The optional keywords give further control of preprocessing.
!ELSEIF

Synonym for !ELSE IF.
!ELSEIFDEF

Synonym for !ELSE IFDEF.
!ELSEIFNDEF

Synonym for !ELSE IFNDEF.
!ENDIF

Marks the end of an !IF, !IFDEF, or !IFNDEF block. Any text after !ENDIF on the same line is ignored.
!UNDEF macro_name

Undefines macro_name.

Expressions in makefile preprocessing

The !IF or !ELSE IF constant_expression consists of integer constants (in decimal or C-language notation), string constants, or commands. Use parentheses to group expressions. Expressions use C-style signed long integer arithmetic; numbers are in 32-bit two's-complement form in the range -2147483648 to 2147483647.

Expressions can use operators that act on constant values, exit codes from commands, strings, macros, and file-system paths.

Makefile preprocessing operators

Makefile preprocessing expressions can use operators that act on constant values, exit codes from commands, strings, macros, and file-system paths. To evaluate the expression, the preprocessor first expands macros, and then executes commands, and then does the operations. It evaluates operations in order of explicit grouping in parentheses, and then in order of operator precedence. The result is a constant value.

The DEFINED operator is a logical operator that acts on a macro name. The expression DEFINED( macro_name ) is true if macro_name is defined, even if it doesn't have an assigned value. DEFINED in combination with !IF or !ELSE IF is equivalent to !IFDEF or !ELSE IFDEF. However, unlike these directives, DEFINED can be used in complex expressions.

The EXIST operator is a logical operator that acts on a file-system path. EXIST( path ) is true if path exists. The result from EXIST can be used in binary expressions. If path contains spaces, enclose it in double quotation marks.

To compare two strings, use the equality (==) operator or the inequality (!=) operator. Enclose strings in double quotation marks.

Integer constants can use the unary operators for numerical negation (-), one's complement (~), and logical negation (!).

Expressions can use the following operators. The operators of equal precedence are grouped together, and the groups are listed in decreasing order of precedence. Unary operators associate with the operand to the right. Binary operators of equal precedence associate operands from left to right.

Operator	Description
`DEFINED(` macro_name `)`	Produces a logical value for the current definition state of macro_name.
`EXIST(` path `)`	Produces a logical value for the existence of a file at path.

`!`	Unary logical NOT.
`~`	Unary one's complement.
`-`	Unary negation.

*``**	Multiplication.
`/`	Division.
`%`	Modulus (remainder).

`+`	Addition.
`-`	Subtraction.

`<<`	Bitwise shift left.
`>>`	Bitwise shift right.

`<=`	Less than or equal.
`>=`	Greater than or equal.
`<`	Less than.
`>`	Greater than.

`==`	Equality.
`!=`	Inequality.

`&`	Bitwise AND.
`^`	Bitwise XOR.
`\|`	Bitwise OR.

`&&`	Logical AND.

`\|\|`	Logical OR.

Note

The bitwise XOR operator (^) is the same as the escape character, and must be escaped (as ^^) when it's used in an expression.

Executing a program in preprocessing

To use a command's exit code during preprocessing, specify the command, with any arguments, within brackets ([ ]). Any macros are expanded before the command is executed. NMAKE replaces the command specification with the command's exit code, which can be used in an expression to control preprocessing.

Example

!IF [my_command.exe arg1 arg2] != 0
!MESSAGE my_command.exe failed!
!ENDIF