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Understanding how C program works
- 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