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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:
- @gcctabopt file.c
C source code which must be preprocessed.
- @gcctabopt file.i
C source code which should not be preprocessed.
- @gcctabopt file.ii
C++ source code which should not be preprocessed.
- @gcctabopt file.m
Objective-C source code. Note that you must link with the ‘libobjc’ library to make an Objective-C program work.
- @gcctabopt file.mi
Objective-C source code which should not be preprocessed.
- @gcctabopt file.mm
- @gcctabopt file.M
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.
- @gcctabopt file.mii
Objective-C++ source code which should not be preprocessed.
- @gcctabopt file.h
C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header.
- @gcctabopt file.cc
- @gcctabopt file.cp
- @gcctabopt file.cxx
- @gcctabopt file.cpp
- @gcctabopt file.CPP
- @gcctabopt file.c++
- @gcctabopt file.C
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.
- @gcctabopt file.hh
- @gcctabopt file.H
C++ header file to be turned into a precompiled header.
- @gcctabopt file.f
- @gcctabopt file.for
- @gcctabopt file.FOR
Fortran source code which should not be preprocessed.
- @gcctabopt file.F
- @gcctabopt file.fpp
- @gcctabopt file.FPP
Fortran source code which must be preprocessed (with the traditional preprocessor).
- @gcctabopt file.r
Fortran source code which must be preprocessed with a RATFOR preprocessor (not included with GCC).
- @gcctabopt file.f90
- @gcctabopt file.f95
Fortran 90/95 source code which should not be preprocessed.
- @gcctabopt file.ads
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.
- @gcctabopt file.adb
Ada source code file containing a library unit body (a subprogram or package body). Such files are also called bodies.
- @gcctabopt file.s
- @gcctabopt file.S
Assembler code which must be preprocessed.
- @gcctabopt other
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:
- @gcctabopt -x language
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 f77 f77-cpp-input ratfor f95 java treelang
- @gcctabopt -x none
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).
- @gcctabopt -pass-exit-codes
gccprogram 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
gccprogram will instead return with numerically highest error produced by any phase that returned an error indication.
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.
- @gcctabopt -c
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.
- @gcctabopt -S
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 file specified.
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.
- @gcctabopt -E
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 standard output.
Input files which don't require preprocessing are ignored.
- @gcctabopt -o file
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.
- @gcctabopt -v
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.
- @gcctabopt -###
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.
- @gcctabopt -pipe
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 no trouble.
- @gcctabopt -combine
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 pre-processed files (one for each source file), but only one (combined) ‘.o’ or ‘.s’ file.
- @gcctabopt –help
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 be displayed.
- @gcctabopt –target-help
Print (on the standard output) a description of target specific command line options for each tool.
- @gcctabopt –version
Display the version number and copyrights of the invoked GCC.
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