CODEWITHSUNDEEP
c++global-variables
Ruchir
Ruchir

Reputation: 845

Changing behavior of "uninitialized local variable" error

Consider the following code:

#include "stdafx.h"
using namespace std;


int _tmain(int argc, _TCHAR* argv[])
{
  int count123;
  for (int c = 0; c < 10; c++)
  {
    count123 += c;
  }

    return 0;
}

Upon compilation I get the warning: warning C4700: uninitialized local variable 'count123' used

I know the reason is declaring count123 but not initializing it.

But if I declare count123 as a global variable as in the code below, the warning disappears. 

#include "stdafx.h"
using namespace std;

int count123;
int _tmain(int argc, _TCHAR* argv[])
{

  for (int c = 0; c < 10; c++)
  {
    count123 += c;
  }

    return 0;
}

As far as I know declaring count123 as a global variable would change its scope but how does that remove the warning? Please guide.

Upvotes: 1

Views: 137

Answers (4)

Nishant
Nishant

Reputation: 1665

Global variables are initialized by zero always, think of a global pointer, initialized with some random value, and you used it in your code mistakenly. Global initialization makes it NULL, so you can check it and use accordingly.

— if it has pointer type, it is initialized to a null pointer;

— if it has arithmetic type, it is initialized to (positive or unsigned) zero;

Upvotes: 2

mazhar islam
mazhar islam

Reputation: 5619

The global variables are initialized with zero by default, hence you got no warnings.

You can easily get the draft of C++ standards then read the section 8.5 Initializers:

10 [ Note: Every object of static storage duration is zero-initialized at program startup before any other initialization takes place. In some cases, additional initialization is done later. —end note ]

Upvotes: 1

Itban Saeed
Itban Saeed

Reputation: 1666

Global variables are static storage variables and these are by default zero-initialized. For more information, please see the answer here.

Upvotes: 2

Christophe
Christophe

Reputation: 73376

The global variables are zero initialized (by the way, the same applies to statics variables). THis is why you don't get this message.

Here the standard quote:

8.5/10: Every object of static storage duration is zero-initialized at program startup before any other initialization takes place. In some cases, additional initialization is done later.

Upvotes: 5

Related Questions