An Introduction to GCC

for the GNU Compilers gcc and g++

Revised and updated

(1) For details see the license file 'COPYING' distributed with GCC.

(2) See https://www.network-theory.co.uk/gcc/intro/

(3) If the prototype of a function has changed, it is necessary to modify and recompile all of the other source files which use it.

(4) This assumes that there is no file called 'clean' in the current directory--see the discussion of "phony targets" in the GNU Make manual for details.

(5) On systems supporting both 64 and 32-bit executables the 64-bit versions of the libraries will often be stored in '/usr/lib64' and '/lib64', with the 32-bit versions in '/usr/lib' and '/lib'.

(6) The actual output shown above may differ, depending on the specific platform and environment.

(7) The default search paths may also include additional system-dependent or site-specific directories, and directories in the GCC installation itself. For example, on 64-bit platforms additional 'lib64' directories may also be searched by default.

(8) In GNU Bash, the shorter form export VARIABLE=VALUE is also allowed.

(9) The current directory can also be specified using an empty path element. For example, :DIR1:DIR2 is equivalent to .:DIR1:DIR2.

(10) Note that the directory containing the shared library can, in principle, be stored ("hard-coded") in the executable itself using the linker option -rpath, but this is not usually done since it creates problems if the library is moved or the executable is copied to another system.

(11) The -D option for defining macros will be explained in detail in the next chapter.

(12) The traditional form of the C language was described in the original C reference manual "The C Programming Language (First Edition)" by Kernighan and Ritchie.

(13) In recent versions of GCC the preprocessor is integrated into the compiler, although a separate cpp command is also provided.

(14) The terminology dates back to the time of magnetic core memory.

(15) Historically, a null pointer corresponded to memory location 0, which is typically restricted to the operating system kernel. In practice this is not always how a null pointer works, but the result is usually the same.

(16) Some systems, such as FreeBSD and Solaris, can also be configured to write core files in specific directories, e.g. '/var/coredumps/', using the sysctl or coreadm commands.

(17) This example uses the ulimit command in the GNU Bash shell. On other systems the usage of the ulimit command may vary, or have a different name (the tcsh shell uses the limit command instead). The size limit for core files can also be set to a specific value in kilobytes.

(18) https://www.network-theory.co.uk/gcc/intro/

(19) Temporary values introduced by the compiler during common subexpression elimination are only used internally, and do not affect real variables. The name of the temporary variable 't' shown above is only used as an illustration.

(20) In this case, the definition of the inline function must be made available to the other files (e.g. in a header file).

(21) Also referred to as "targeting" a specific processor.

(22) In recent versions of GCC this option has been renamed to -mtune. The older form -mcpu will continue to work.

(23) On GNU/Linux systems, the command cat /proc/cpuinfo will display information about the CPU.

(24) Intel has added support for this instruction set as the "Intel 64-bit enhancements" on their Xeon CPUs.

(25) The options -maix64 and -maix32 are used on AIX.

(26) Motorola 68k processors also use extended precision registers, like the x86.

(27) For quantities held in the x87 extended-precision registers the relative precision is 5.42*10^-20 and the exponent range is 10^(+/-4932) . Standard double precision values have a relative precision of 2.22*10^-16 and an exponent range of 10^(+/-308) .

(28) The operating system saves and restores the control word when switching between processes, so that each process maintains its own setting.

(29) MacOS X (Darwin) on PowerPC uses signed char, for consistency with other Darwin architectures.

(30) There is also a subtle error even on platforms with signed char---the ASCII character 255 is spuriously interpreted as an end of file condition.

(31) If displayed, character code 255 often appears as ÿ.

(32) Alternatively, the appropriate paths can be set up in gdb using the file and directory commands.

(33) Note that ar does not require a prefix '-' for its options.

(34) American Mathematical Monthly, Volume 92 (1985), 3--23

(35) As mentioned earlier, the preprocessor is integrated into the compiler in recent versions of GCC. Conceptually, the compilation process is the same as running the preprocessor as separate application.

(36) The MSB and LSB orderings are also known as big-endian and little-endian respectively (the terms originate from Jonathan Swift's satire "Gulliver's Travels", 1727).

(37) POSIX.1 (2003 edition), IEEE Std 1003.1-2003.

(38) https://www.gnu.org/prep/service.html

(39) https://www.network-theory.co.uk/gcc/intro/

(40) https://order.fsf.org/

(41) https://www.network-theory.co.uk/gcc/intro/