How to use g++
GNU provides are a publicly-available
optimizing compilers (translator) for C, C++, Ada 95, and Objective C that
currently runs under various implementations of Unix (plus VMS as well
as OS/2 and perhaps other PC systems) on a variety of processors too numerous
to mention. You can find full documentation on-line under Emacs (use C-h
i and select the ``GCC'' menu option). You don't need to know much
about it for our purposes. This document is a brief summary. (Note that
g++ and gcc are, for most practical purposes, identical
programs. Running g++ is nearly the same as gcc -lg++.
Consequently, when looking at GNU's online documentation using Emacs info,
gcc is where you'll look.) Also, you can try man g++.
Running the compiler
You can use g++ both to compile programs into object modules and
to link these object modules together into a single program. It looks at
the names of the files you give it to determine what language they are
in and what to do with them. Files of the form name.cc (or name.cpp)
are assumed to be C++ files and files matching name.o are assumed
to be object (i.e., machine-language) files. To translate a C++ source
file, file.cc, into a corresponding object file, file.o,
use the g++ command:
g++ -c compile-options file.cc
To link one or more object files, file1.o, file2.o, ...,
to produced from C++ files into a single executable file called prog,
use the following command:
g++ -o prog link-options file1.o file2.o ... other-libraries
(The options and libraries clauses are described below.)
You can bunch these two steps---compilation and linking---into one with
the following command.
g++ -o prog compile-and-link-options file1.cc file2.cc ... other-libraries
examples: g++ -o test1 test1.cpp
g++ -ansi -o prog2 fig02_07.cpp
g++ -g -o prog3 fig02_09.cpp
g++ -Wall -g prog4 fig02_21.cpp -lm
After linking has produced an executable file called prog, it becomes,
in effect, a new Unix command, which you can run with
where arguments denotes any command-line arguments to the program.
A library is a collection of object files that has been grouped
together into a single file and indexed. When the linking command encounters
a library in its list of object files to link, it looks to see if preceding
object files contained calls to functions not yet defined that are defined
in one of the library's object files. When it finds such a function, it
then links in the appropriate object file from the library. One library
gets added to the list of libraries automatically, and provides a number
of standard functions common to C++ and C.
Libraries are usually designated with an argument of the form -llibrary-name.
In particular, -lg++ denotes a library of standard C++ routines
and -lm denotes a library containing various mathematical routines
(sine, cosine, arctan, square root, etc.) They must be listed after
the object or source files that contain calls to their functions.
The following compile- and link-options will be of particular interest
-c (Compilation option)
Compile only. Produces .o files from source files without doing
-Dname=value (Compilation option)
In the program being compiled, define name as if there were a line
#define name value
at the beginning of the program. The ` = value' part may
be left off, in which case value defaults to 1.
-o file-name (Link option, usually)
Use file-name as the name of the file produced by g++ (usually,
this is an executable file).
-llibrary-name (Link option)
Link in the specified library. See above. (Link option).
-g (Compilation and link option)
Put debugging information for gdb into the object or executable
file. Should be specified for both compilation and linking.
-MM (Compilation option)
Print the header files (other than standard headers) used by each source
file in a format acceptable to make. Don't produce a .o
file or an executable.
-pg (Compilation and link option)
Put profiling instructions for generating profiling information for gprof
into the object or executable file. Should be specified for both
compilation or linking. Profiling is the process of measuring how
long various portions of your program take to execute. When you specify
-pg, the resulting executable program, when run, will produce
a file of statistics. A program called gprof will then produce
a listing from that file telling how much time was spent executing each
-Wall (Compilation option)
Produce warning messages about a number of things that are legal but dubious.
I strongly suggest that you always specify this and that you treat
every warning as an error to be fixed.