To define an inference rule, use the following syntax:
.fromext.toext:
commands
The first line lists two extensions: fromext represents the extension of a dependent file, and toext represents the extension of a target file. Extensions are not case sensitive. Macros can be invoked to represent fromext and toext; the macros are expanded during preprocessing.
The period (.) preceding fromext must appear at the beginning of the line. The colon (:) can be preceded by zero or more spaces or tabs; it can be followed only by spaces or tabs, a semicolon (;) to specify a command, a number sign (#) to specify a comment, or a newline character. No other spaces are allowed.
The rest of the inference rule gives the commands to be run if the dependency is out-of-date. Use the same rules for commands in inference rules as in description blocks. (See “Commands”.)
Summary: An inference rule applies to a single target and dependent.
An inference rule can be used only when a target and dependent have the same base name. You cannot use a rule to match multiple targets or dependents. For example, you cannot define an inference rule that replaces several modules in a library because all but one of the modules must have a different base name from the target library.
Summary: Inference rules apply only to files with extensions listed in .SUFFIXES.
Inference rules can exist only for dependents with extensions that are listed in the .SUFFIXES directive. (For information on .SUFFIXES, see “Dot Directives”.) If an out-of-date dependency does not have a commands block, and if the .SUFFIXES list contains the extension of the dependent, NMAKE looks for an inference rule matching the extensions of the target and of an existing file in the current or specified directory. If more than one rule matches existing dependent files, NMAKE uses the order of the .SUFFIXES list to determine which rule to invoke. Priority in the list descends from left to right. NMAKE may invoke a rule for an inferred dependent even if an explicit dependent is specified; for more information, see “Inferred Dependents”.
Summary: Inference rules can make a makefile unnecessary.
Inference rules tell NMAKE how to build a target specified on the command line if no makefile is provided or if the makefile does not have a dependency containing the specified target. When a target is specified on the command line and NMAKE cannot find a description block to run, it looks for an inference rule to tell it how to build the target. You can run NMAKE without a makefile if the inference rules that are predefined or defined in TOOLS.INI are all you need for your build.