3 GCC Command Options

When you invoke GCC, it normally does preprocessing, compilation, assembly and linking. The “overall options” allow you to stop this process at an intermediate stage. For example, the -c option says not to run the linker. Then the output consists of object files output by the assembler. See Options Controlling the Kind of Output.

Other options are passed on to one or more stages of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them.

Most of the command-line options that you can use with GCC are useful for C programs; when an option is only useful with another language (usually C++), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages.

The usual way to run GCC is to run the executable called gcc, or machine-gcc when cross-compiling, or machine-gcc-version to run a specific version of GCC. When you compile C++ programs, you should invoke GCC as g++ instead. See Compiling C++ Programs, for information about the differences in behavior between gcc and g++ when compiling C++ programs.

The gcc program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may not be grouped: -dv is very different from ‘-d -v’.

You can mix options and other arguments. For the most part, the order you use doesn’t matter. Order does matter when you use several options of the same kind; for example, if you specify -L more than once, the directories are searched in the order specified. Also, the placement of the -l option is significant.

Many options have long names starting with ‘-f’ or with ‘-W’—for example, -fmove-loop-invariants, -Wformat and so on. Most of these have both positive and negative forms; the negative form of -ffoo is -fno-foo. This manual documents only one of these two forms, whichever one is not the default.

Some options take one or more arguments typically separated either by a space or by the equals sign (‘=’) from the option name. Unless documented otherwise, an argument can be either numeric or a string. Numeric arguments must typically be small unsigned decimal or hexadecimal integers. Hexadecimal arguments must begin with the ‘0x’ prefix. Arguments to options that specify a size threshold of some sort may be arbitrarily large decimal or hexadecimal integers followed by a byte size suffix designating a multiple of bytes such as kB and KiB for kilobyte and kibibyte, respectively, MB and MiB for megabyte and mebibyte, GB and GiB for gigabyte and gigibyte, and so on. Such arguments are designated by byte-size in the following text. Refer to the NIST, IEC, and other relevant national and international standards for the full listing and explanation of the binary and decimal byte size prefixes.

See Option Index, for an index to GCC’s options.

• Option Summary:		Brief list of all options, without explanations.
• Overall Options:		Controlling the kind of output: an executable, object files, assembler files, or preprocessed source.
• Invoking G++:		Compiling C++ programs.
• C Dialect Options:		Controlling the variant of C language compiled.
• C++ Dialect Options:		Variations on C++.
• Objective-C and Objective-C++ Dialect Options:		Variations on Objective-C and Objective-C++.
• Diagnostic Message Formatting Options:		Controlling how diagnostics should be formatted.
• Warning Options:		How picky should the compiler be?
• Debugging Options:		Producing debuggable code.
• Optimize Options:		How much optimization?
• Instrumentation Options:		Enabling profiling and extra run-time error checking.
• Preprocessor Options:		Controlling header files and macro definitions. Also, getting dependency information for Make.
• Assembler Options:		Passing options to the assembler.
• Link Options:		Specifying libraries and so on.
• Directory Options:		Where to find header files and libraries. Where to find the compiler executable files.
• Code Gen Options:		Specifying conventions for function calls, data layout and register usage.
• Developer Options:		Printing GCC configuration info, statistics, and debugging dumps.
• Submodel Options:		Target-specific options, such as compiling for a specific processor variant.
• Spec Files:		How to pass switches to sub-processes.
• Environment Variables:		Env vars that affect GCC.
• Precompiled Headers:		Compiling a header once, and using it many times.

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