Introduction to GCC and G++

HelloWorld in C

Here is the classic HelloWorld program in C: (source file)

#include <stdio.h>

int main ()
{
  printf ("Hello World!\n");
}

Note:

• The #include command is a preprocessor directive to load the stdio library.
• Execution starts in a function (method) called main:
  • There are other signatures for main as we will see.
  • Although a return type is declared, nothing needs to be returned.
• The printf method is used for screen output.
• The "newline" character \n is explicitly required.

Compiling and executing on Unix:

• The program above is a plain text file, as in any programming language.
• The file extension needs to be .c.
• The file name need not be helloworld.
• To compile:

    gcc -o helloworld helloworld.c
    

• This produces an executable called helloworld which can be executed as:

    helloworld
    

  or, if you don't have the current directory in your path:

    ./helloworld

  #include <iostream>
  
  int 
  main ()
  {
    std::cout << "Hello, world!\n";
    return 0;
  }
  
  
  The program can be compiled with the following command line:
  $ g++ -Wall hello.cc -o hello
  
  
  The C++ frontend of GCC uses many of the same the same options as the C compiler gcc. It also supports some additional options for controlling C++ language features, which will be described in this chapter. Note that C++ source code should be given one of the valid C++ file extensions ‘.cc’, ‘.cpp’, ‘.cxx’ or ‘.C’ rather than the ‘.c’ extension used for C programs.
  
  The resulting executable can be run in exactly same way as the C version, simply by typing its filename:
  $ ./hello
  Hello, world!
  

  $ g++ -Wall -c hello.cc
  $ gcc hello.o       (should use g++)
  hello.o: In function `main':
  hello.o(.text+0x1b): undefined reference to `std::cout'
  .....
  hello.o(.eh_frame+0x11): 
    undefined reference to `__gxx_personality_v0'
  
  
  Undefined references to internal run-time library functions, such as __gxx_personality_v0, are also a symptom of linking C++ object files with gcc instead of g++. Linking the same object file with g++ supplies all the necessary C++ libraries and will produce a working executable:
  $ g++ hello.o
  $ ./a.out
  Hello, world!
  

  http://www.network-theory.co.uk/docs/gccintro/gccintro_54.html

  http://www.seas.gwu.edu/~simhaweb/C/lectures/module1/module1.html