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In this how to, compilation of C++ sources will be demonstrated using the g++ compiler under Linux. A description of a Windows-based compiler is given in Compiling with the Dev-C++ compiler.

g++ is a free C++ compiler, it is part of the GNU Compiler Collection. If you use the Linux operating system then there is a good chance that g++ is already installed; open a command shell and type

  $ g++ --version

This short document explains how to perform basic g++ compilations.

// Output the recipe for pancakes. #include <iostream> using namespace std; int main() { int i; cout << "Some milk," << endl; cout << "some water," << endl; cout << "an egg," << endl; cout << "some salt.\n" << endl; cout << "Mix and fry." << endl; return 0; }

Some milk, some walter, an egg, some salt. Mix and fry.

Basic compilation

To compile to an executable called pancake the basic command is:

  $ g++ pancake.cpp -o pancake

The program can be executed by typing pancake or you may need to give the path as follows

  $ ./pancake

  $ man g++

  $ g++ -Wall pancake.cpp -o pancake
  pancake.cpp: In function 'int main()':
  pancake.cpp:7: warning: unused variable 'i'

Compiling multiple sources

Multiple sources can be compiled into a single executable as follows:

  $ g++ powers.cpp power1.cpp power2.cpp power3.cpp -o powers

// Outputs a value raised to the power of 1, 2, and 3.
#include <iostream>
#include "power1.h"
#include "power2.h"
#include "power3.h"

int main() {
  double x=2.5;
  std::cout << power1(x) << " "
            << power2(x) << " "
            << power3(x) << std::endl;
}

2.5 6.25 15.625

Function power1.cpp and it's header file power1.h

// Returns a value to the power of 1 double power1(double a) { return a; }

#ifndef POWER1_H #define POWER1_H // Prototype for function power1() // returns a value to the power of 1 double power1(double); #endif

Function power2.cpp and it's header file power2.h

// Returns a value to the power of 2 double power2(double a) { return a*a; }

#ifndef POWER2_H #define POWER2_H // Prototype for function power2() // returns a value to the power of 2 double power2(double); #endif

Function power3.cpp and it's header file power3.h

// Returns a value to the power of 3 double power3(double a) { return a*a*a; }

#ifndef POWER3_H #define POWER3_H // Prototype for function power3() // returns a value to the power of 3 double power3(double); #endif

Creating and linking object files

The compilation:

  $ g++ powers.cpp power1.cpp power2.cpp power3.cpp -o powers

  $ g++ powers.cpp power1.o power2.o power3.o -o powers

  $ g++ -c power1.cpp
  $ g++ -c power2.cpp
  $ g++ -c power3.cpp

Creating and linking library files

The object files created in the previous section can be placed into a single library which can then be linked during compilation. This is achieved by using the archive tool ar (see man ar for details).

Object files can be placed in a library for example as follows:

  $ ar rcvf libsubs.a power1.o power2.o power3.o

More objects can be added to the library with:

  $ ar rcvf libsubs.a another.o

The contents of a library can be listed with:

  $ ar tv libsubs.a

Functions in the library can be listed with:

  $ nm libsubs.a

Objects can be deleted from the library with:

  $ ar dv libsubs.a power1.o

Once a library has been created, it can be linked in a compilation as follows:

  $ g++ powers.cpp -L. -lsubs -o powers

The -L. options tells the linker that the library can be found in the current directory. If the library is not in the current directory then you should give the path, for example:

  $ g++ powers.cpp -L/home/fred/cpp/lib/ -lsubs -o powers

  $ g++ powers.cpp -L$MYLIB -lsubs -o powers

  $ MYLIB=/home/fred/cpp/lib/