How to print value of global variable and local variable having same name?

Question

Here is my code , I want to print 15 and 12 but due to instance member hiding the local value of a is getting printed twice.

#include <stdio.h>                                  
int a = 12;             
int main()          
{           
    int a = 15;             
    printf("Inside a's main local a = : %d\n",a);                  
    printf("In a global a = %d\n",a);            
    return 0;           
}

Why and is there any way to print it in c ? ... BTW I know it in c++.

@ tuğrul büyükışık ..... That's not working how does my program know about the filename of that code itself... It will give compilation error. It's not correct — Omkant, Aug 30 '12 at 05:35
@gsamaras: I don't think it's appropriate to edit someone else's code for such a small cosmetic change (adding spaces around `=`), when the original code was perfectly correct. I won't revert the edit because that wouldn't be helpful either. — Keith Thompson, Jul 19 '16 at 01:44
@KeithThompson you are right, sorry! I was dragged here by a new (wrong) answer. My goal was to fully edit that question and then wanted to abandoned the edit, but instead of hitting the cancel button, I tried to do that manually and forgot that it was that way. Really sorry. — gsamaras, Jul 19 '16 at 02:03
@gsamaras: Ok, stuff happens. IMHO it looks slightly better with the spaces. Not a big deal either way. — Keith Thompson, Jul 19 '16 at 02:05

score 26 · Accepted Answer · answered Aug 29 '12 at 18:05

26

Use the extern specifier in a new compound statement.

This way:

#include <stdio.h>      

int a = 12;             

int main(void)          
{           
    int a = 15;             
    printf("Inside a's main local a = : %d\n", a);

    {
        extern int a;
        printf("In a global a = %d\n", a);
    }

    return 0; 
}

answered Aug 29 '12 at 18:05

ouah

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now it shadows the inner a=15 :) what if he wants that a=15 in the innermost brackets :) – huseyin tugrul buyukisik Aug 29 '12 at 18:10
@tuğrulbüyükışık but not after the `}` of the new compound statement. – ouah Aug 29 '12 at 18:12
there isnt something like "super" isnt it? Yeah i know :) – huseyin tugrul buyukisik Aug 29 '12 at 18:13
3

@tuğrulbüyükışık this is C, not Java! ;) – ouah Aug 29 '12 at 18:15
Hi , When I tried extern int i; without { }, it thrown error. and when I simply put that { }, I got the answer. Why is the { } bracess requried ? what does it do? – Sorcrer Dec 31 '15 at 15:38
3

@Sorcrer the new block `{}` creates a new scope; the `a` identifier declared in the inner scope hides the `a` identifier declared in the outer scope. – ouah Dec 31 '15 at 15:50

score 3 · Answer 2 · answered Aug 31 '12 at 00:05

I know this doesn't directly answer your question, but the best way to do this is to change the name of the local variable so it doesn't conflict with the name of the global variable.

If you have control of the code inside the function (i.e., you can add an extern declaration to make the global variable visible), then you can just as easily change the name of the variable.

It's impossible to tell what name would be better. In practice, the variables will undoubtedly have more descriptive names than a. The way they're used should give you some guidance about good names for them.

If they actually serve the same purpose, they probably don't both need to exist. You might remove variable that's local to main(), or, perhaps better, remove the global and pass the local (or its address) to other functions that need to access it.

score 1 · Answer 3 · edited Aug 30 '12 at 23:53

1

I think i found my answer in a way... it works

#include <stdio.h>

int a = 5;


int main()
{
    int a=10;
    if(1)
    {
        extern int a;
        printf("global: %d\n", a);
    }
    printf("local: %d\n", a);
    return 0;
}

edited Aug 30 '12 at 23:53

Daniel Fischer

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answered Aug 30 '12 at 08:08

Omkant

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No need for the `if(1)`; you can just have a simple compound statement. – Keith Thompson Aug 30 '12 at 23:58
@Mr.32: Yeah I know ..but see the accepted answer please ..It's just the other way to do this.. – Omkant Nov 08 '12 at 05:55

score -1 · Answer 4 · edited Jul 19 '16 at 01:05

-1

add :: for global ambit

#include <stdio.h>                                  
int a=12;             
int main()          
{           
  int a=15;             
  printf("Inside a's main local a = : %d\n",a);                  
  printf("In a global a = %d\n",::a);            
  return 0;           
}

edited Jul 19 '16 at 01:05

gsamaras

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answered Jul 19 '16 at 01:00

Jaime Francisco

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The question is about C, not C++. – Retired Ninja Jul 19 '16 at 01:06

How to print value of global variable and local variable having same name?

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