Difference between revisions of "Advance-C/C2/Storage-class-specifiers/English-timed"
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| − | | For this tutorial I am using | + | | For this tutorial I am using '''Ubuntu Operating system version 11.10''' and '''gcc Compiler version 4.6.1 on Ubuntu''' |
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Revision as of 11:25, 20 November 2015
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| 00:01 | Welcome to the spoken tutorial on Storage class specifiers. |
| 00:07 | In this tutorial, We will learn about
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| 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:
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| 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 statment. |
| 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 uparrow 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 + Shft + 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 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 initalize 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 throughtout 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-
|
| 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 |
| 10:04 | Watch the video available at the link shown below |
| 10:07 | It summarises the Spoken Tutorial project |
| 10:11 | If you do not have good bandwidth, you can download and watch it |
| 10:16 | The Spoken Tutorial Project Team, Conducts workshops using spoken tutorials |
| 10:22 | Gives certificates to those who pass an online test
For more details, please write to contact@spoken-tutorial.org |
| 10:33 | Spoken Tutorial Project is a part of the Talk to a Teacher project |
| 10:38 | It is supported by the National Mission on Education through ICT, MHRD, Government of India |
| 10:45 | More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro |
| 10:52 | This is Ashwini Patil from IIT Bombay. Thank you for joining. |
