Variable Modifiers − Auto & Extern

Programming & Data Structures: Auto and extern variable modifiers in C programming.
Topics discussed:
1. Auto modifier.
2. Extern modifier.
3. Extern modifier examples.
4. Procedure to create a project and different files within that project.
C Programming Lectures: goo.gl/7Eh2SS
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Axol x Alex Skrindo - You [NCS Release]
#CProgrammingByNeso #CProgramming #VariableModifiers

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[@Ribulose15diphosphat]

And Wrong: 1. auto is the opposite of register. Declaring a variable as auto, prevents compiler-optimisation to turn it into a register-variable. Typically you want register-variables in inner loop, but declare variables of the outer loop first, so delare the variables for the outer loop as auto. 2. Global variables are not initialized to zero. If your system/compiler does that - nice - but the C-standards says there is garbage.

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at 1:43 , I haven't initialized a variable in main function and by printing that variable,it gave me as 0 but not a garbage value.

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[@atharvanaik2434]

GCC didn't compile program with auto keyword. It throws error:two or more data types in declaration of 'var'. While, cl(MSVC) printed 0.

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[@mukulmalviya1605]

use of uninitialized local variables leads to undefined behaviour. It depends on the compiler, in the visual studio community if we print the value of uninitialized variable it gives compile-time error while in GCC compiler it prints 0

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[@krut4rth]

@2:35 int var; // It is just declared, not defined.. // definition is when you assign memory to it with = operator

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Awesome explanation!!

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[@sayanmondal1387]

sir extern int a; doesn't work in my code blocks what should I do? my main.c #include extern int a; int main() { printf("%d", a); return 0; } and my other.c int a = 56;

[@saiprasadjetti2175]

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[@ojasvvgupta5639]

at 9.52 even if we dont write extern in main then also it will print 9 as we have already defined the global variable then why to use extern.

[@zizomohamed9015]

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[@tezlallc2900]

At 8:41 on Video 14 (Variable Modifier - Static) you place a variable outside the scope of any function and specifically call it global. Thus it retains its value and should be accessible to main which is within a completely different file. If this is true then why the need for extern? It appears to me that you cannot compile when you delete the line extern within main here in this video which seems to suggest just the opposite of Video 14 which is to say that int a= 5; is NOT really global after all.

[@Atsushi549]

9:41 , do we still need to use extern int for accessing global variable?

[@sudipkumarmondal136]

Sir, in my computer auto variable does not give garbage values it also initializes with 0 as same as global variable.

[@mateuszlukaszczyk5359]

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[@lakshmimanasamanasa5052]

@7:28 -> external variable declared is a global variable for that file right? All the global variables are by default initialized to 0, isn't it? why don't it give the output as 0 and instead giving an error?

[@sruthimajhi5610]

Great one sir!

[@avitiwari7921]

Good Explanation What if there are multiple files with int a declaration and defination and a single extern int a in main file? If memory is not provided to extern int a, so when does the exact value and memory for variable a is filled?

[@karthikbankapur3520]

sir I had tried to print output for an integer(not initialized) but instead of printing any random garbage value it prints 0 all the time. why so?

[@vineetverma6645]

was it global?

[@riturajpathak1905]

same and it was not global

[@princedhiman8714]

@@riturajpathak1905varies according to machine properties

[@gauravkumeriya376]

@@riturajpathak1905 ya but it is unpredictible in latest version of gcc. see geeks for geeks

[@parsikarudhirbabu9462]

it happened for me too

[@vikassaini1935]

this is gold

[@prasadsawant9122]

Thanks for sharing so many small small details , not only for this topic but all topics in all of your videos ... I do have one question here for extern What if we declare int a = something in two different files and try to refer in our main file using extern ..which one it will refer?

[@compangit1524]

I will just leave a comment for myself. Feel free to comment, thanks. Global variables are initialized to 0 by default. Extern is short for external. It declares the variable but no definition (though you can also define it), therefore no memory allocated to it. This is used when we want access a variable of the same name but located and defined in the nearest outer scope which can also include other files in the current workspace. It avoids redifinition or having to find another variable name for the same variable. Autos can't be declared multiple times, but externs can be. Declaration then definition. Initialize == define.

[@saiprasadjetti2175]

Nice explanation

[@Sabari-gd3fw]

Hi sir, Thanks for this useful content. I have one query in this , at 10:03 you told if extern variable don't have definition in current file, it will go and search other files to retrieve the definition..my question here is which file it takes first to search the definition of this extern variable...because in your case you have created only one "other.c" file...but in reality there are lot of files will be there.If I am varying that extern variables in multiple files which file definition it will consider first?

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better than my professor and his slides😅

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informative lecture....thanx sr...

[@chiragchirag4649]

Will these concepts of system level features be used in other programing language like python?????????

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Masterpiece

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[@shiprajha8304]

when i keep the variable global and uninitialized, its showing compilation error and for local variable (not initialized) its showing 0 and not garbage value....why is that?

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JUST AMAZING!!

[@anupriyarani6902]

Sir then What is the use of auto modifier ,if it doesn't change anything in program.

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[@frezajoe5836]

now, what is the pros of external keyword, if we can just include one file in another in order to access his declared globale variable instead of those geeky flashy gamic extern keyword?

[@Zer0_byte]

dear sir i try it what i notice is when i auto char auto float is value is expect 0 also unsigned int

[@panthasaleheen4952]

What I think is, the extern variable works like the complement set. 'A' complement is equal to universal set minus 'A' set.

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thanks alot

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nice one

[@RiseAayush]

The output when i use var in form of global variable as well as in the scope gives the output as same as 0. What would be the reason behind it????????

[@ProProgrammer-ss4gb]

Are the notes of these lectures available somewhere...? And how can i access them...?

[@omkumarsingh4194]

If I define variable int a =3; inside some function say func() then , I write extern int a; in main() and printf ("%d",a); Whether it will show 3 or error.

[@abhaypratap9898]

Error

[@himanshichoudhary8778]

Thanks

[@techbeginners3816]

1:44 sir what is garbage value and how it is printed?

[@namitasharma5201]

can't thank you enough

[@JE-SyedAteebShah]

Does [extern int var] always need to be a global variable???????

[@yagneshacharya2461]

what if we create more than 2 files like i created 3 files and declaring int a = 2 and int a = 3 , and then i write extern int a in my 1st file , so when i write printf(a) what will print?

[@harshbhadani537]

In my project there is not any (other.cpp) file what should i do to add that.

[@dachinoloko7624]

Hi thanks for the lessons I appreciate it very much. However, I have a question. I tried not intializing my variable with int var; and also with auto int var; where both are actually the same in the local scope. The result I obtained was zero instead of indeterminate/random/garbage value. Why is that so? This means the int var; in local is the same as if I declare it globally since int var; in global is always zero. Thank you and hope to hear your explanation when you're free. Cheers!

[@Daisy-xs9yb]

int var in local getting zero is not the same as int var in global because when you declare a global variable the initial or the default value is zero but a local variable stores a random number so if you get a local variable equal zero then it is just a coincidence maybe if u give local int var another time it will give a diff ans. hope it helps

[@destinyobamwonyi8865]

if you are a nerdy nerd like my self and you are using vim or emacs you can access the variable by compiling the two files, like this "gcc main.c other.c -o main". where main is the executable.

[@jaisuriyar5259]

but I am getting this error for extern: collect2.exe: error: ld returned 1 exit status

[@esma2856]

10:00 I wrote the same as you wrote (int a = 5; in the file "other.c") but I got the error. Error is:multiple definition of 'a'. Why did this happen? And how can I fix it?

[@clementnathanael3085]

u use vscode or what?

[@arbajkhan042]

​@@clementnathanael3085 vs code

[@dr.anubhavkumarprasad5765]

extern int a=10; extern int a; //do not have this name variable in any other file Above code do not produce error. Multiple declaration is allowed which is ok, but second line is linking to variable in same scope ?

[@snehchauhan8507]

Yes exactly. By writing extern int a=10; it means both declaration and definition

[@mathematics_rajkumar]

For me 'auto int var' giving 0 as output, when I won't initialize var, is garbage value?

[@puneetkorjani6648]

but when i don't initialize the auto variabe still it is showing 0 value not any garbage values??