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2.  Compilation stages of C program
 How C program works
 Object file format
 How to run hello world program in Linux
environment

3.  C created -1972 by Dennis Ritchie
 Efficient
 Portable
 Flexible

4.  Three things are necessary for creating
programs
• Text editor (vi editor)
• Compiler (gcc)
• Standard libraries and headers (glibc)

5.  Assembly Machine Language
• MOV R1, 0x1000 ------ 10101010
• MOV R2, 0x1004 ------ 11001100
• ADD R1, R2 ------ 11100011
• STA 0x1008 ------ 10001000
 HLL (C program)
• C = a+b

6.  Each and every statement of C program need
to convert in such a format so that processor
can understand it.
 Ex: Processor does not understand what is
“printf”
 A program that translate HLL language to
machine level language is known as compiler

7.  The four stages for a C program to become
an executable
• Pre-processing
• Compilation
• Assembly
• Linking

8.  Begins with „#‟
 Carried out prior to compilation
 Macro substitution
 Comments are removed
 Expansion of the included files
 Saved in .i file
/* hello.c */
#include<stdio.h> /*Preprocessor directives*/
int main()
{
printf(“Hello Worldn”);
return 0;
}

9.  “hello.i” is the input to Compiler
 Compiled into intermediate stage (assembly)
i.e. „hello.s”
/* hello.c */
#include<stdio.h> /*Preprocessor directives*/
int main()
{
printf(“Hello Worldn”);
return 0;
}

10.  “hello.s” is the input to Assembler
 Compiled into object file “hello.o”
/* hello.c */
#include<stdio.h> /*Preprocessor directives*/
int main()
{
printf(“Hello Worldn”);
return 0;
}

11.  Final stage
 “hello.o” is the input to linker
 Form executable a.out
/* hello.c */
#include<stdio.h> /*Preprocessor directives*/
int main()
{
printf(“Hello Worldn”);
return 0;
}

13.  Input Program Output
 src code >Preprocessor >expanded src code
 expanded src code >Compiler >assembly src code
 assembly code >Assembler >object code
 object code >Linker >executable code
 executable code >Loader >execution

14.  Part of Operating system responsible for
loading the program
 Allocates program address space
 Copies a program into main memory

15.  Stands for Executable and Linkable Format
 Object file
 Executables
 Shared libraries

16.  Each object file contains
• code section
• data section
• BSS (Block started by Symbol) section
• symbol table
 Symbol table contains information of
• global variable,
• external functions like printf, scanf
• Functions defined in other object file

17.  not specific to particular processor or
architecture
 adopted to many operating systems on many
different platforms

19.  Combines code and data sections
 Resolves symbols for global variable
 Resolves symbols for external function and
library function such as printf, scanf

20.  What is Library?
It is a collection of pre-compiled functions and
reusable code.
 In Linux, it is called glibc (GNU C library)

21. Library
Static Library Shared Library
Dynamic Dynamic Loading
Linking

23.  Link at the compilation stage into the final
executable
 Size of the executable becomes large
compared to shared library
 Need more RAM
 Fast
 Suitable for small program

24.  It just verifies the link
 Actual symbol is added at the time of running
 Size of executable become less as compared
to Static
 Becomes slower than static library
 Used for bigger application

25.  C language is
• Efficient
• Powerful
• Flexible
 Its being 40 years it is used extensively and
will be used for many more years to come.
 Encourage yourself to be a good programmer
to sustain in software industry