Advance-C/C2/Storage-class-specifiers/English-timed

Time	Narration
00:01	Welcome to the Spoken Tutorial on Storage class specifiers.
00:07	In this tutorial, We will learn about: Storage class specifiers auto keyword static keyword extern keyword register keyword, with the help of examples.
00:22	For this tutorial, I am using: Ubuntu Operating system version 11.10 and gcc Compiler version 4.6.1 on Ubuntu.
00:34	To follow this tutorial, you should be familiar with 'C' tutorials.
00:41	If not, for relevant tutorials, please visit our website which is as shown.
00:47	I will start with an introduction to storage class specifiers.
00:52	Specifiers tell the compiler- * where to store a variable
00:57	* How to store the variable
00:59	* What is the initial value of the variable
01:03	* Life time of the variable.
01:06	The Syntax is: storage_specifier data_type variable _name
01:13	Types of storage class specifiers are: auto static extern register .
01:21	Let us start with auto keyword.
01:24	auto keyword declares an automatic variable.
01:28	It has a local scope.
01:30	Keywords are not initialized automatically.
01:34	You should explicitly initialize keywords while declaring.
01:39	Storage space of keywords is CPU memory.
01:43	Let us see an example. I have a code file; let us go through it.
01:49	Note that our filename is auto.c.
01:54	We have declared a function as “increment()”.
01:58	This is the main() function.
02:00	In the main() function, increment() function is called 4 times.
02:06	Then we have the return 0 statement.
02:10	Let us see the function definition.
02:14	Here, we have declared variable 'i' as auto int. It has a local scope.
02:21	Then we display value of 'i' using printf.
02:26	Value of i is incremented here.
02:30	Let us open the terminal by pressing Ctrl+Alt+T keys simultaneously on your keyboard.
02:38	Type: gcc space auto.c space hyphen o space auto. Press Enter.
02:48	Type: dot slash auto
02:51	The output is zero.
02:54	Now come back to our program.
02:57	Let us initialize the auto variable i above the main() function.
03:02	I will cut this declaration and initialization from here and paste it over here. Click on Save.
03:14	Let us execute on the terminal. Press the up-arrow key twice. Press Enter.
03:22	We get an error: "file-scope declaration of 'i' specifies 'auto'" .
03:29	This is because an auto variable is local to the function.
03:34	We cannot initialize it globally.
03:37	Let us fix the error. Come back to our program.
03:42	Delete this; paste it over here.
03:47	Click on Save and execute on the terminal.
03:52	Press the up-arrow key. Recall the previous command.
03:57	Press Enter. Type: dot slash auto. Press Enter.
04:03	Yes, it is working! The output is zero.
04:07	This is because we have initialized the value of 'i' as zero.
04:13	Now, let us see static variable.
04:16	Although we have studied about static variable in the previous tutorials, I will explain it here briefly.
04:24	'static' variables are initialized to zero.
04:28	They are not destroyed even after program control exits from the block.
04:35	Value of the variable persists between different function calls.
04:41	Storage space is CPU memory.
04:45	Let us see an example. I will edit the same code file.
04:51	Come back to our program.
04:54	Press Ctrl + Shift + S keys simultaneously.
05:01	Now, I will just change the filename as static. Click on Save.
05:10	Now, I will change the initialization of the variable 'i' to static int i equal to zero Click on Save.
05:23	Let us see what happens. Execute the file on the terminal.
05:30	Type: gcc space static.c space hyphen o space stat. Press Enter.
05:41	Type: dot slash stat. Press Enter.
05:46	The output is displayed as: "0, 1, 2, 3"
05:51	This is because, static variables are global variables.
05:56	The scope of static variable is local to the function, they are defined in.
06:03	They do not lose their value between function calls.
06:08	Now, let us learn about extern keyword.
06:12	Scope of extern variable is throughout the main program.
06:17	Definition for extern variable might be anywhere in the 'C' program.
06:23	extern variables are initialized to zero, by default.
06:28	They can be accessed by all functions in the program.
06:33	These are stored in CPU memory.
06:36	Let us see an example.
06:38	I have a code file; let us go through it.
06:42	Note that our filename is "extern.c".
06:47	I have initialized a variable as integer variable 'x' to 10.
06:54	This is the main() function. In the main() function, I have declared an extern integer variable y.
07:03	Using the printf statements, we will display the values of x and y. This is the return statement.
07:12	We will initialize 'y' to 50 after the main() function close.
07:18	Now, switch to the terminal and let us see what will be the output.
07:24	Type: gcc space extern.c space hyphen o space ext. Press Enter.
07:35	Type: dot slash ext. Press Enter.
07:40	The output is displayed as: The value of x is 10 The value of y is 50
07:48	As we studied, the value of the extern keyword is through out the main program.
07:55	We can define it anywhere in the program.
07:59	Both the statements are justified.
08:02	Now, let us move on to register keyword.
08:06	register variables will be accessed faster than normal variables.
08:13	They are stored in register memory rather than main memory.
08:19	Limited number of variables can be used since register size is very low.
08:25	16 bits, 32 bits or 64 bits.
08:30	Let us see an example now. I have a code file. Let us go through it.
08:37	Note that the file name is register.c
08:42	Here, we have declared register integer variable.
08:47	This variable will be directly stored in the register memory.
08:53	This is the 'for' loop that displays the value of 'i' from 1 to 5.
08:59	This will display the value of 'i'.
09:03	Let us execute the program and see.
09:07	On the terminal, type: gcc space register.c space hyphen o space register
09:17	Press Enter. Type: dot slash register. Press Enter.
09:25	You can see, the output is displayed as: "Values stored in register memory 1 2 3 4 5".
09:34	This brings us to the end of this tutorial. Let us summarize.
09:39	In this tutorial, we learnt- Storage class specifiers auto keyword static keyword extern keyword register keyword
09:52	As an assignment, write a program to print the sum of first 5 numbers.
09:59	Declare both the keywords auto and static in the program.
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10:52	This is Ashwini Patil from IIT Bombay. Thank you for joining.

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PoojaMoolya, Pratik kamble, Sandhya.np14