gcc is the "GNU" C Compiler, and g++ is the "GNU C++ compiler, while cc and CC are the Sun C and C++ compilers also available on Sun workstations. Below are several examples that show how to use g++ to compile C++ programs, although much of the information applies to C programs as well as compiling with the other compilers.

Example 1: Compiling a simple program

  #include "iostream.h"
  int main() 
  {
    cout << "Hello\n";
  } 

  g++ hello.C -o hello 

This command compiles hello.C into an executable program named "hello" that you run by typing 'hello' at the command line. It does nothing more than print the word "hello" on the screen.

  g++ -c hello.C
  g++ hello.o -o hello 

The end result is the same, but this two-step method first compiles hello.C into a machine code file named "hello.o" and then links hello.o with some system libraries to produce the final program "hello". In fact the first method also does this two-stage process of compiling and linking, but the stages are done transparently, and the intermediate file "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 commonly used options. In each example, "myprog.C" contains C++ source code for the executable "myprog". In most cases options can be combined, although it is generally not useful to use "debugging" and "optimization" options together.

Compile myprog.C so that myprog contains symbolic information that enables it to be debugged with the gdb debugger.

g++ -g myprog.C -o myprog

Have the compiler generate many warnings about syntactically correct but questionable looking code. It is good practice to always use this 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 -O is 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

Compile a C program that uses math functions such as "sqrt".

gcc myprog.C -o myprog -lm

Compile a C program with the "electric fence" library. This library, available on all the Linux machines, causes many incorrectly written programs to crash as soon as an error occurs. It is useful for debugging as the error location can be quickly determined using gdb. However, it should only be used for debugging as the executable myprog will be much slower and use much more memory than usual.

gcc -g myprog.C -o myprog -lefence

Example 2: Compiling a program with multiple source files

  g++ file1.C file2.C -o myprog 

  g++ -c file1.C
  g++ -c file2.C
  g++ file1.o file2.o -o myprog 

  g++ -c file1.C
  g++ file1.o file2.o -o myprog