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Initializing the shadow copy variable

Is there anything in the standard that defines the initialization of a variable from the variable it shadows?

For example:

int i = 7;
{
    int i = i;
}

Visual Studio 2013 allows this without warning and works as expected. The internal variable i

is 7. Clang and GCC, however, give me a warning about initializing the initializing variable from itself, will be uninitialized.

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2 answers


The standard has something to say:

3.3.2 Declaration point [basic.scope.pdecl]

1 Declaration point for a name immediately after its full declaration (Clause 8) and before its initializer (if any), except as noted below. [Example:

int x = 12;
{ int x = x; }

Here the second x is initialized with its own (undefined) value. -end example]



This is exactly your case. The program demonstrates undefined behavior by accessing an uninitialized object.

My copy of VS2013 reports error C4700: uninitialized local variable 'i' used

for this code. Not sure why your copy is behaving differently.

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If the first variable is defined in a namespace like the global namespace, you can write using your qualified name



int i = 7;

int main()
{
   int i = ::i;
   //...
}
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