Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. The first three stages apply to an individual source file, and end by producing an object file; 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:
You can specify the input language explicitly with the -x option:
-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 objective-c c++ c-header cpp-output c++-cpp-output assembler assembler-with-cpp
-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).
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.
-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.
-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.
Since only one output file can be specified, it does not make sense to use -o when compiling more than one input file, unless you are producing an executable file as output.
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 , and all preprocessed C source on standard output.
-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.
-pipe
(Not available on Windows NT) 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.
See See Hardware Models and Configurations for information on the -arch flag, which allows you to specify the target platform when compiling on Mach.