1. C/C++ Programming Environment
Few Basics
Sanjaya Karunasena

2. Outline What is a Computer Program?
How to create a Computer Program using C/C++
Execution of a Computer Program
Control flow

3. A Computer Program What is a Program? What is a Computer Program?
A program is a planned sequence and combination of activities designed to achieve specified goals. [
What is a Computer Program?
A set of instructions that direct a computer to carry out a given task. [

4. A Computer Program cont.
In a typical computer (Von Neumann Architecture)
A program resides in some permanent storage (Disk – File System, ROM, NVRAM, etc)
When it is executed, it gets loaded in to the memory (RAM)
Then instructions are fetched in to the CPU and executed

5. Program Creation A Programming Language can be used
To write a Program, any Text Editor can be used
But an Integrated Development Environment (IDE) makes our life easier
Following file extensions typically belongs to C/C++ code files
Source Files
Header Files
*.c
*.h
*.cc
*.chh
*.cpp
*.hpp
*.c++
*.h++
*.cxx
*.hxx

6. Program Creation cont.
A compiler should be used compile the code written
gcc, cc, g++, c++ : Some Unix C/C++ compilers
cl.exe : Compiler Linker comes with Microsoft Visual Studio
The compiler produces Common Object File Format (COFF – UNIX and Windows systems) or Executable and Linkable Format (ELF – Most UNIX systems) files called Object Files or Object Code
*.o in UNIX
*.obj in Windows

7. Program Creation cont. *.h Files *.h Files Pre-Processor Compiler
Object File
*.cpp File
*.cpp File
Linker
Static Library
Object File
Executable
Note: A Static Library is a collection of object files

8. Program Creation cont.
A Linker should be used to link the Object Files with other Object Files and Libraries
ld in UNIX
link.exe, comes with Microsoft Visual Studio
The Linker produces the executable file(s) or libraries
*.exe, *.lib, *.dll in Windows
a.out default but can be given any name, *.bin, *.a, *.so in UNIX
An interpreted program is executed using an Interpreter (No need to compile)
VB, JavaScript, PERL, TCL

9. Program Execution Machine Program In Memory Load into Memory Dynamic
Library
Executable
Note: Kernel API has functions (CreateProcess, fork) which can be used to load and execute a program

10. IDE, Compiler and Linker
IDEs, Compilers and Linkers are also Programs
How did the first Compiler / Linker created?
This is not a Chicken and Egg problem

11. The Main Function
The main function of a C/C++ program could be of couple of forms
In C
int main (void)
In C++
int main ( )
In C/C++
int main (int argc, char ** argv)
In Windows GUI Applications
int WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
When a program is executed the C/C++ run time environment calls this function

12. The Main Function cont.
You cannot call main from within a program or take the address of main
You cannot overload this function
This is the programmer’s entry point to a program
What is the system entry point to a program?

13. C Run-Time Startup
C Run-Time Startup could be of many forms depend on the type of the application
Function name
Default for
mainCRTStartup (or wmainCRTStartup)
An application using /SUBSYSTEM:CONSOLE; calls main (or wmain)
WinMainCRTStartup (or wWinMainCRTStartup)
An application using /SUBSYSTEM:WINDOWS; calls WinMain (or wWinMain), which must be defined with __stdcall
_DllMainCRTStartup
A DLL; calls DllMain, which must be defined with __stdcall, if it exists

14. C Run-Time Startup cont.
The C/C++ compiler implements system entry point, mainCRTStartup function for us
By default the linker appoint mainCRTStartup function as the system entry point to a program (A different function can be given with the linker option “/ENTRY:function”)
Hence the system calls mainCRTStartup
The mainCRTStartup calls our main function

15. Actual Execution Flow main mainCRTStartup KERNEL EXECUTABLE Initialize
Get Environment Variables
Call to main
Clean up
Your Program Code
main
mainCRTStartup
KERNEL
EXECUTABLE

16. void main()
The ISO C++ Standard (ISO/IEC 14882:1998) specifically requires main to return int
But the ISO C Standard (ISO/IEC 9899:1999) actually does not
If the return type is not compatible with int, the termination status returned to the host environment is unspecified
This sounds dangerous
However most of the compilers takes cares of this problem for us
It’s either return 0 by default or won’t allow you to implement a main function without a return type

17. Summary
A program is a set of instructions that directs a computer to carry out a given task
A programming language can be used to create a program
IDE, compiler, and linker plays an important role
In a C/C++ program, Programmer’s entry point is the main function
By default system entry point to a C/C++ program is “mainCRTStartup”

18. For next couple of weeks…
We need to quickly come up to the speed with basic C/C++ programming
We are going to learn some thing very interesting, Object Orientation!
Next week -> Introduction to Pointers
Following is good tutorial

19. For next couple of weeks…
Please follow the following sections in order
Intro to C++ The basics of C++
If statements If statements, and some boolean information
Loops in C++ All you want to know about loops
Functions Functions...all about them, making and using the critters
Switch case About the switch case structure
Pointers Using pointers to access memory locations
Structures Structures, all about 'em, and how to use 'em
Arrays All about arrays
Strings About character arrays (strings)
File I/O About file i/o
Typecasting Typecasting: making variables look like another data-type
Command line arguments How to accept command line arguments (AND checking file existence)
Recursion Recursion--a function calling itself
Formatted Output in C++ using iomanip Learn how to create nicely formatted output in C++
Understanding the C Preprocessor -- Constants, Macros, and other Tricks Learn how to use the C preprocessor

20. References http://www.delorie.com/djgpp/v2faq/faq22_25.html