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

CH03.fm Page 61 Monday, October 7, 2002 8:33 PM
Compiling a Program 61
This means that if you use command gcc hello.c, GCC will consider hello.c as a
C program and will invoke appropriate helper programs to build the output. However, if you use
gcc hello.cpp command, GCC will consider hello.cpp as a C++ program and will
compile it accordingly. You can also select a language type with a particular file using –x command
line option. Table 3-2 lists languages that can be selected with this option.
Table 3-2 Selecting languages with –x option.
Option
Language
-x c (lowercase c) C language selection
-x c++ C++ file
-x objective-c Objective C
-x assembler Assembler file
-x f77 Fortran file
-x java Java language file
Note that –x option applies to all the files that follow until you turn it off using the –x
none option on the command line. This is especially important when you use the GNU make
utility discussed in Chapter 5.
By default, the object file created by GCC has .o extension, replacing the original extension
of the file. You can create output file with a particular name using –o command line option.
The following command creates test.o file from hello.c.
gcc –c hello.c –o test.o
3.3.3 Compiling to Intermediate Levels
The compilation process involves many steps like preprocessing, assembling and linking.
By default GCC carries out all of these processes and generates executable code as you have
seen earlier. However, you can force GCC not to do all of these steps. For example, using the –c
command line option, the gcc command will only compile a source code file and will not generate
executable object code. As you already know, the following command compiles file
hello.c and creates an object file hello.o.
gcc –c hello.c
If you look at the type of the newly created object file using the file command, you can
see that this is not a linked file. This is shown in the following command output.
[root@conformix chap-03]# file hello.o
hello.o: ELF 32-bit LSB relocatable, Intel 80386, version 1,
not stripped
[root@conformix chap-03]#