Learning C
3 min readFeb 3, 2021
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.
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.
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. 
