gcc is the "GNU" C Compiler, and g++ is the "GNUC++ compiler, while cc and CC are the Sun C and C++ compilers also available on Sun workstations. Below are several examples that showhow to use g++ to compile C++ programs, although much of the informationapplies to C programs as well as compiling with the other compilers.
Example 1: Compiling a simple program
Consider the following example: Let "hello.C" be a file that contains the following C++ code.
#include "iostream.h" int main() { cout << "Hello\n"; } The standard way to compile this program is with the command
g++ hello.C -o hello
This command compiles hello.C into an executable program named "hello" thatyou run by typing 'hello' at the command line. It does nothing more thanprint the word "hello" on the screen.
Alternatively, the above program could be compiled using the followingtwo commands.
g++ -c hello.C g++ hello.o -o hello
The end result is the same, but this two-step method first compiles hello.Cinto a machine code file named "hello.o" and then links hello.owith some system libraries to produce the final program "hello".In fact the first method also does this two-stage process of compilingand linking, but the stages are done transparently, and the intermediatefile "hello.o" is deleted in the process.
Frequently used compilation options
C and C++ compilers allow for many options for how to compile a program,and the examples below demonstrate how to use many of the more commonlyused options. In each example, "myprog.C" contains C++ sourcecode for the executable "myprog". In most cases options canbe combined, although it is generally not useful to use "debugging" and "optimization" optionstogether.
- Compile myprog.C so that myprog contains symbolicinformation that enables it to be debugged with the gdb debugger.
g++ -g myprog.C -o myprog
- Have the compiler generate many warnings about syntacticallycorrect but questionable looking code. It is good practice to always usethis option with gcc and g++.
g++ -Wall myprog.C -o myprog
- Generate symbolic information for gdb and many warning messages.
g++ -g -Wall myprog.C -o myprog
- Generate optimized code on a Solaris machine with warnings. The -Ois a capital o and not the number 0!
g++ -Wall -O -mv8 myprog.C -o myprog
- Generate optimized code on a Solaris machine using Sun's own CC compiler.This code will generally be faster than g++ optimized code.
CC -fast myprog.C -o myprog
- Generate optimized code on a Linux machine.
g++ -O myprog.C -o myprog
- Compile myprog.C when it contains Xlib graphics routines.
g++ myprog.C -o myprog -lX11
If "myprog.c" is a C program, then the above commands will all work byreplacing g++ with gcc and "myprog.C" with "myprog.c". Beloware a few examples that apply only to C programs.
- Compile a C program that uses math functions suchas "sqrt".
gcc myprog.C -o myprog -lm
- Compile a C program with the "electric fence" library. Thislibrary, available on all the Linux machines, causes many incorrectlywritten programs to crash as soon as an error occurs. It is useful fordebugging as the error location can be quickly determined using gdb.However, it should only be used for debugging as the executable myprogwill be much slower and use much more memory than usual.
gcc -g myprog.C -o myprog -lefence
Example 2: Compiling a program with multiple sourcefiles
If the source code is in several files, say "file1.C" and "file2.C",then they can be compiled into an executable program named "myprog" usingthe following command:
g++ file1.C file2.C -o myprog
The same result can be achieved using the following three commands:
g++ -c file1.C g++ -c file2.C g++ file1.o file2.o -o myprog
The advantage of the second method is that it compiles each of the sourcefiles separately. If, for instance, the above commands were used to create "myprog",and "file1.C" was subsequently modified, then the followingcommands would correctly update "myprog".
g++ -c file1.C g++ file1.o file2.o -o myprog
Note that file2.C does not need to be recompiled, so the time requiredto rebuild myprog is shorter than if the first method for compiling myprogwere used. When there are numerous source file, and a change is only madeto one of them, the time savings can be significant. This process, thoughsomewhat complicated, is generally handled automatically by a makefile.
