The Linux Development Platform Configuring, Using, and ... - Classes

CH03.fm Page 59 Monday, October 7, 2002 8:33 PM
Compiling a Program 59
is used. These Makefiles contain information about how the compiler will be invoked and what
command line switches will be used. Information about GNU make and Makefiles is presented
in Chapter 5.
3.3.1 Simple Compilation
Consider the following C source code file, which is named hello.c. We shall frequently
refer to this program in this as well as coming chapters.
#include
main ()
{
printf("Hello world\n");
}
To compile this file, you just need to run the following command.
[rr@conformix 4]$ gcc hello.c
[rr@conformix 4]$
By default, this command will generate an output file named a.out, which can be executed
on the command line as follows:
[rr@conformix 4]$ ./a.out
Hello world
[rr@conformix 4]$
Note that regardless of the name of your source code file, the name of the output file is
always a.out. You may actually know what an ordinary a.out file is, but this isn't one of
them. It is an elf file, despite its name. If you want to create an output file with a different
name, you have to use the –o command line option. The following command creates an output
file with name hello.
gcc hello.c -o hello
As you may have noted, the above commands do both the compiling and linking processes
in a single step. If you don’t want to link the program, then simple compilation of hello.c file
can be done with the following command. The output file will be hello.o and will contain
object code.
gcc –c hello.c
Note that both –c and –o command line switches can be used simultaneously. The following
command compiles hello.c and produces an output file test.o which is not yet linked.
gcc –c hello.c -o test.o
Usually when you compile many files in a project, you don’t create a.out files. Either
you compile many files into object files and then link them together into an application or make
executables with the same name as the source code file.