Question

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Is this self initialization valid?

Is this a well-defined C/C++ program or not?

int foo = foo;

int main()
{

}

Would foo be zero-initialized, or is it undefined behaviour?

Answer 1

It is an ill-formed C program. In C initializers for objects with static storage duration must be constant expressions. The foo on the right-hand side is not a constant expression.

In C++ it is well-formed and has defined behavior, because of zero-initialization of objects with static storage duration (which takes place before any other initialization).