2.9 Options Controlling the Preprocessor

These options control the C preprocessor, which is run on each C source file before actual compilation.

If you use the `-E' option, nothing is done except preprocessing. Some of these options make sense only together with `-E' because they cause the preprocessor output to be unsuitable for actual compilation.

-include file

Process file as input before processing the regular input file. In effect, the contents of file are compiled first. Any `-D' and `-U' options on the command line are always processed before `-include file', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are written.

-imacros file

Process file as input, discarding the resulting output, before processing the regular input file. Because the output generated from file is discarded, the only effect of `-imacros file' is to make the macros defined in file available for use in the main input.

Any `-D' and `-U' options on the command line are always processed before `-imacros file', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are written.

-idirafter dir

Add the directory dir to the second include path. The directories on the second include path are searched when a header file is not found in any of the directories in the main include path (the one that `-I' adds to).

-iprefix prefix

Specify prefix as the prefix for subsequent `-iwithprefix' options.

-iwithprefix dir

Add a directory to the second include path. The directory's name is made by concatenating prefix and dir, where prefix was specified previously with `-iprefix'. If you have not specified a prefix yet, the directory containing the installed passes of the compiler is used as the default.

-iwithprefixbefore dir

Add a directory to the main include path. The directory's name is made by concatenating prefix and dir, as in the case of `-iwithprefix'.

-isystem dir

Add a directory to the beginning of the second include path, marking it as a system directory, so that it gets the same special treatment as is applied to the standard system directories.

-nostdinc

Do not search the standard system directories for header files. Only the directories you have specified with `-I' options (and the current directory, if appropriate) are searched. See section Options for Directory Search, for information on `-I'.

By using both `-nostdinc' and `-I-', you can limit the include-file search path to only those directories you specify explicitly.

-undef

Do not predefine any nonstandard macros. (Including architecture flags).

-E

Run only the C preprocessor. Preprocess all the C source files specified and output the results to standard output or to the specified output file.

-C

Tell the preprocessor not to discard comments. Used with the `-E' option.

-P

Tell the preprocessor not to generate `#line' directives. Used with the `-E' option.

-M

Tell the preprocessor to output a rule suitable for make describing the dependencies of each object file. For each source file, the preprocessor outputs one make-rule whose target is the object file name for that source file and whose dependencies are all the #include header files it uses. This rule may be a single line or may be continued with `\'-newline if it is long. The list of rules is printed on standard output instead of the preprocessed C program.

`-M' implies `-E'.

Another way to specify output of a make rule is by setting the environment variable DEPENDENCIES_OUTPUT (see section Environment Variables Affecting GCC).

-MM

Like `-M' but the output mentions only the user header files included with `#include "file"'. System header files included with `#include <file>' are omitted.

-MD

Like `-M' but the dependency information is written to a file made by replacing ".c" with ".d" at the end of the input file names. This is in addition to compiling the file as specified--`-MD' does not inhibit ordinary compilation the way `-M' does.

In Mach, you can use the utility md to merge multiple dependency files into a single dependency file suitable for using with the `make' command.

-MMD

Like `-MD' except mention only user header files, not system header files.

-MG

Treat missing header files as generated files and assume they live in the same directory as the source file. If you specify `-MG', you must also specify either `-M' or `-MM'. `-MG' is not supported with `-MD' or `-MMD'.

-H

Print the name of each header file used, in addition to other normal activities.

-Aquestion(answer)

Assert the answer answer for question, in case it is tested with a preprocessing conditional such as `#if #question(answer)'. `-A-' disables the standard assertions that normally describe the target machine.

-Dmacro

Define macro macro with the string `1' as its definition.

-Dmacro=defn

Define macro macro as defn. All instances of `-D' on the command line are processed before any `-U' options.

-Umacro

Undefine macro macro. `-U' options are evaluated after all `-D' options, but before any `-include' and `-imacros' options.

-dM

Tell the preprocessor to output only a list of the macro definitions that are in effect at the end of preprocessing. Used with the `-E' option.

-dD

Tell the preprocessing to pass all macro definitions into the output, in their proper sequence in the rest of the output.

-dN

Like `-dD' except that the macro arguments and contents are omitted. Only `#define name' is included in the output.

-trigraphs

Support ANSI C trigraphs. The `-ansi' option also has this effect.

-Wp,option

Pass option as an option to the preprocessor. If option contains commas, it is split into multiple options at the commas.

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