ACS - University of Gaziantep

C/C++ programming under Linux (a very basic introduction)

Revised 24/02/2008

On the University central Linux servers (gul3, gul4, gul5), the C/C++ compiler command is g++
though for simple compilations you can use the command: c

  $ edit hello.c
  ----------------------------------------
  #include <iostream>
  using namespace std;

  int main() {
    cout << "Hello World!" << endl;
  }
  ----------------------------------------

To compile the file 'hello.c'
$ c hello.c
or use g++ with -o option
$ g++ hello.c -o hello
To execute the file 'hello'
$ hello

This will output "Hello World!".
Notes:

The source files must have the extension .c or .cc or .cxx or .cpp or .CPP or .c++ or .C.
The executable has no extension (it does NOT have the DOS or VMS extension .exe)
You can pass one extra compiler option by adding the option after the filename,

Full c/c++ compilation options (e.g. linking objects and libraries)
can be gained by using the g++ command (try g++ --help or man g++ etc)

Creating and using libraries
First create the following example files:
sub1.c , sub2.c , sub3.c and main.c

You can compile and link all four files as follows:
$ g++ main.c sub1.c sub2.c sub3.c -o main
Then, the command
main
will output
The sum is 5 The product is 6 The largest is 3

Alternatively the files can be compiled individually to create objects files (compile without linking) for linking later
$ g++ sub1.c -c $ g++ sub2.c -c $ g++ sub3.c -c
These commands create the object files sub1.o, sub2.o and sub3.o

Creating Libraries (ar)
A library whose name is test of these functions can be created as follows:
$ ar rcvf libtest.a sub1.o sub2.o sub3.o (see man ar)
You can add more objects to the library with:
$ ar rcvf libtest.a sub4.o
To list the contents of the library:
$ ar tv libtest.a
To list functions in a library:
$ nm libtest.a (see man nm)
To delete an object from the library:
$ ar dv libtest.a sub3.o

To link the library when compiling a C++ program main.c which requires sub1.o , sub2.o and sub3.o:
$ g++ main.c -o main -L. -ltest
Note that lib and .a are dropped.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:
$ g++ main.c -o main -L/home/yilmaz/C/lib -ltest
or
$ g++ main.c -o main -L$MYLIB -ltest
with
MYLIB=/home/yilmaz/C/lib

system@gantep.edu.tr