Using g++Most of this document was taken nearly verbatim from Paul Hilfinger. Any errors introduced, however, are David Wolfe's or Karl Knight's.
IntroductionGNU provides 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 iand 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.)
Running the compilerYou 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.cpp) are assumed to be C++ files and files matching
name.oare 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++ -c compile-options file.ccTo link one or more object files,
file2.o, ..., 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-librariesAfter linking has produced an executable file called prog, it becomes, in effect, a new Unix command, which you can run with
./prog argumentswhere arguments denotes any command-line arguments to the program.
LibrariesA 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.
OptionsThe following compile- and link-options will be of particular interest to us.
- Compile only. Produces
.ofiles from source files without doing any linking.
-Dname=value (Compilation option)
- In the program being compiled, define name as if there
were a line
#define name valueat the beginning of the program. The `
= value' part may be left off, in which case value defaults to 1.
-ofile-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).
-Idirectory-name (Link option)
- Add the specified directory to the list of directories to be searched for header files. (Link option).
-g(Compilation and link option)
Put debugging information for
gdbinto the object or executable file. Should be specified for both compilation and linking.
Print the header files (other than standard headers) used by each
source file in a format acceptable to
make. Don't produce a
.ofile or an executable.
-pg(Compilation and link option)
Put profiling instructions for generating profiling information for
gprofinto 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
gprofwill then produce a listing from that file telling how much time was spent executing each function.
- Produce warning messages about a number of things that are legal but dubious. If you were compiling from the command line, I would strongly suggest that you always specify this and that you treat every warning as an error to be fixed. If you are using an IDE like Eclipse, this options is not generally needed.