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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[@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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[@MJ-dq8om]

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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[@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?

[@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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[@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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Nice explanation

[@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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[@techbeginners3816]

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

[@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?

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[@sudipkumarmondal136]

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

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Thanks

[@true4189]

Thank u

[@pragyapatel7335]

Does the memory of extern variable destroyed when the program done executing?

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[@sriharsha8802]

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 this happens ?

[@Dontever_throw_trash_out]

can anyone tell what extern int function will assign its value when the whole operation is performed in any online compilers or any other online compiler

[@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.

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Short and to the point videos, finally I found the course I needed. Thank you so much for all your effort. _/\_

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Complete c please neso!

[@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

[@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?

[@syedhazim9957]

what will happen if there are multiple files that have defined variable 'a' Which file's value of a will the compiler access?

[@krut4rth]

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

[@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

[@ashishsinha8893]

sir plz upload videos all as soon as possible my examination is near about placement interviews.... plz sir if possible

[@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?

[@sharadraj338]

tried to initialise an exten variable which already existed in other file, it throws error as -->>" [Error] 'a' has both 'extern' and initializer " always ? please explain sir !

[@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?

[@anupriyarani6902]

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

[@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????????

[@vijayanks1714]

What compiler u have use sir...

[@mahdarif4957]

if I have multiple files with in a project and all the files have same variable with different definition, which value will the extern int takes??

[@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?

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Please anyone tell me,are these lectures are enogh for gate 22 ..please.

[@tejaschitnis154]

can a linker assign a value from another project file? is there any such case? why not?

[@thestoicway001]

Sir my local variable is also returning 0 all time

[@MK-or5zl]

What if i multiple files are created and each of then having same var name and different values

[@currentxchange]

When using another compiler (gpp in atom) it didn't work at all. Perhaps no linker? Undefined symbols for architecture x86_64: "_dd", referenced from: _main in main-f1adc3.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation)

[@chiragchirag4649]

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

[@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

[@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

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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;

[@ProProgrammer-ss4gb]

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

[@adithyagalipelli2934]

can't we use extern modifier inside the main function?