Compiling And Linking
C systems generally consist of several parts: a
program development environment, the language and the C Standard Library. C programs typically go through six phases to be
executed. These are: edit, preprocess, compile, link, load and execute.
Creating a Program
Edit a file. This is accomplished with an editor
program. Software packages for the C/C++ integrated program development
environments such as Eclipse, Codeblock and Microsoft Visual Studio have
editors that are integrated into the programming environment.
You type a C
program with the editor, make corrections if necessary, and then store the
program on a secondary storage device such as a hard disk. C program file names
should end with the .c extension or save it directly.
Preprocessing and Compiling a C Program
Here you give the command to compile the program.
The compiler translates the C program into machine language-code (also referred
to as object code). In a C system, a preprocessor program executes automatically
before the compiler’s translation phase begins.
The C preprocessor obeys special commands called
preprocessor directives, which indicate that certain manipulations are to be
performed on the program before compilation. These manipulations usually consist
of including other files in the file to be compiled and performing various text
replacements. The most common preprocessor directives will discussed soon.
The compiler
translates the C program into machine-language code. A syntax error occurs when
the compiler cannot recognize a statement because it violates the rules of the
language. The compiler issues an error message to help you locate and fix the
incorrect statement. The C Standard does not specify the wording for error
messages issued by the compiler, so the error messages you see on your system
may differ from those on other systems. Syntax errors are also called compile
errors, or compile-time errors.
Source codes in C are saved with .C file extension.
Header files or library files have the .H file extension. Every time a program
source code is successfully compiled, it creates an .OBJ object file, and an
executable .EXE file.
Linking
The next phase is called linking. C programs
typically contain references to functions defined elsewhere, such as in the
standard libraries or in the private libraries of groups of programmers working
on a particular project. The object code produced by the C compiler typically
contains “holes” due to these missing parts. A linker links the object code
with the code for the missing functions to produce an executable image (with no
missing pieces). Compile and link a program If the program compiles and links
correctly, a file called .out is produced.
Loading
The next phase is called loading. Before a program
can be executed, the program must first be placed in memory. This is done by
the loader, which takes the executable image from disk and transfers it to
memory. Additional components from shared libraries that support the program
are also loaded.
Execution
Finally, the computer, under the control of its CPU,
executes the program one instruction at a time. To load and execute the program
on a Linux system, type ./a.out at the Linux prompt and press Enter.
