3.2 Options Controlling the Kind of Output
Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. GCC is capable of preprocessing and compiling several files either into several assembler input files, or into one assembler input file; then each assembler input file produces an object file, and linking combines all the object files (those newly compiled, and those specified as input) into an executable file.
For any given input file, the file name suffix determines what kind of compilation is done:
- C source code which must be preprocessed.
- C source code which should not be preprocessed.
- C++ source code which should not be preprocessed.
- Objective-C source code. Note that you must link with the libobjc
library to make an Objective-C program work.
- Objective-C source code which should not be preprocessed.
- Objective-C++ source code. Note that you must link with the libobjc
library to make an Objective-C++ program work. Note that `.M' refers
to a literal capital M.
- Objective-C++ source code which should not be preprocessed.
- C, C++, Objective-C or Objective-C++ header file to be turned into a
- C++ source code which must be preprocessed. Note that in `.cxx',
the last two letters must both be literally `x'. Likewise,
`.C' refers to a literal capital C.
- Objective-C++ source code which must be preprocessed.
- Objective-C++ source code which should not be preprocessed.
- C++ header file to be turned into a precompiled header.
- Fixed form Fortran source code which should not be preprocessed.
- Fixed form Fortran source code which must be preprocessed (with the traditional
- Free form Fortran source code which should not be preprocessed.
- Free form Fortran source code which must be preprocessed (with the
- Ada source code file which contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called specs.
- Ada source code file containing a library unit body (a subprogram or
package body). Such files are also called bodies.
Assembler code. Apple's version of GCC runs the preprocessor
on these files as well as those ending in `.S'.
- Assembler code which must be preprocessed.
- An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way.
You can specify the input language explicitly with the -x option:
- Specify explicitly the language for the following input files
(rather than letting the compiler choose a default based on the file
name suffix). This option applies to all following input files until
the next -x option. Possible values for language are:
c c-header c-cpp-output c++ c++-header c++-cpp-output objective-c objective-c-header objective-c-cpp-output objective-c++ objective-c++-header objective-c++-cpp-output assembler assembler-with-cpp ada f95 f95-cpp-input java treelang
- Turn off any specification of a language, so that subsequent files are
handled according to their file name suffixes (as they are if -x
has not been used at all).
- These are similar in effect to -x objective-c and -x
objective-c++, but affect only the choice of compiler for files already
identified as source files. (APPLE ONLY)
- Compile for the specified target architecture arch. The
allowable values are `i386', `x86_64', `ppc' and
`ppc64'. Multiple options work, and direct the compiler to
produce “universal” binaries including object code for each
architecture specified with -arch. This option only works if
assembler and libraries are available for each architecture specified.
- Apply option to the command line for architecture arch.
This is useful for specifying an option that should only apply to
one architecture when building a “universal” binary. (APPLE ONLY)
- Save debug info in separate object file.
This is available only while building PCH in -gfull mode.
- Normally the gcc program will exit with the code of 1 if any phase of the compiler returns a non-success return code. If you specify -pass-exit-codes, the gcc program will instead return with numerically highest error produced by any phase that returned an error indication. The C, C++, and Fortran frontends return 4, if an internal compiler error is encountered.
If you only want some of the stages of compilation, you can use -x (or filename suffixes) to tell gcc where to start, and one of the options -c, -S, or -E to say where gcc is to stop. Note that some combinations (for example, `-x cpp-output -E') instruct gcc to do nothing at all.
- Compile or assemble the source files, but do not link. The linking
stage simply is not done. The ultimate output is in the form of an
object file for each source file.
By default, the object file name for a source file is made by replacing the suffix `.c', `.i', `.s', etc., with `.o'.
Unrecognized input files, not requiring compilation or assembly, are ignored.
- Stop after the stage of compilation proper; do not assemble. The output
is in the form of an assembler code file for each non-assembler input
By default, the assembler file name for a source file is made by replacing the suffix `.c', `.i', etc., with `.s'.
Input files that don't require compilation are ignored.
- Stop after the preprocessing stage; do not run the compiler proper. The
output is in the form of preprocessed source code, which is sent to the
Input files which don't require preprocessing are ignored.
- Place output in file file. This applies regardless to whatever
sort of output is being produced, whether it be an executable file,
an object file, an assembler file or preprocessed C code.
If -o is not specified, the default is to put an executable file in a.out, the object file for source.suffix in source.o, its assembler file in source.s, a precompiled header file in source.suffix.gch, and all preprocessed C source on standard output.
- Print (on standard error output) the commands executed to run the stages
of compilation. Also print the version number of the compiler driver
program and of the preprocessor and the compiler proper.
- Like -v except the commands are not executed and all command
arguments are quoted. This is useful for shell scripts to capture the
driver-generated command lines.
- Use pipes rather than temporary files for communication between the
various stages of compilation. This fails to work on some systems where
the assembler is unable to read from a pipe; but the GNU assembler has
- If you are compiling multiple source files, this option tells the driver
to pass all the source files to the compiler at once (for those
languages for which the compiler can handle this). This will allow
intermodule analysis (IMA) to be performed by the compiler. Currently the only
language for which this is supported is C. If you pass source files for
multiple languages to the driver, using this option, the driver will invoke
the compiler(s) that support IMA once each, passing each compiler all the
source files appropriate for it. For those languages that do not support
IMA this option will be ignored, and the compiler will be invoked once for
each source file in that language. If you use this option in conjunction
with -save-temps, the compiler will generate multiple
(one for each source file), but only one (combined) .o or
- Print (on the standard output) a description of the command line options
understood by gcc. If the -v option is also specified
then --help will also be passed on to the various processes
invoked by gcc, so that they can display the command line options
they accept. If the -Wextra option is also specified then command
line options which have no documentation associated with them will also
- Print (on the standard output) a description of target specific command
line options for each tool.
- Display the version number and copyrights of the invoked GCC.
- Read command-line options from file. The options read are
inserted in place of the original @file option. If file
does not exist, or cannot be read, then the option will be treated
literally, and not removed.
Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively.