Compiling a simple C program using GCC

Let us see how to compile a simple C program using gcc compiler, for this we will try out with classical hello world program in C language which is given below:

#include <stdio.h>
int main (void)
{
printf ("Hello, world!\n");
return 0;
}

We will save the above 'C' code in a file named 'hello.c'. Inorder to compile a C file with gcc, use the following command:

[bash]$ gcc -Wall hello.c -o hello

This compiles the source code in ‘hello.c’ to machine code and stores it in an executable file ‘hello’.

NOTE: The output file for the machine code is specified using the -o option. This option is usually given as the last argument on the command line. If it is omitted, the output is written to a default file called ‘a.out’. If a file with the same name as the executable file already exists in the current directory it will be overwritten.

The option -Wall turns on all the most commonly-used compiler warnings---it is recommended that you always use this option! There are many other warning options, but -Wall is the most important. GCC will not produce any warnings unless they are enabled. Compiler warnings are an essential aid in detecting problems when programming in C and C++.

In this case, the compiler does not produce any warnings with the -Wall option, since the program is completely valid. Source code which does not produce any warnings is said to compile cleanly.

To run the program, type the path name of the executable like this:

[bash]$ ./hello
Hello, world!

This loads the executable file into memory and causes the CPU to begin executing the instructions contained within it. The path ./ refers to the current directory, so ./hello loads and runs the executable file ‘hello’ located in the current directory.

For a detailed view about how the who compilation process goes checkout Compilation process in GCC.