What standard clause mandates this lvalue-to-rvalue conversion?

Question

Given:

int main() {
   int x = 0;
   int y = x; // <---
}

Could someone please tell me which clause of the standard (2003 preferred) man

Answer 1

The initializer has the follwing grammar:

initializer:
        = initializer-clause
        ( expression-list )

initializer-clause:
    assignment-expression
    { initializer-list ,opt }
    { }

In your example, x is an assignment-expression which follows this chain of grammar productions:

conditional-expression  ==>
    logical-or-expression ==>
        logical-and-expression  ==>
            inclusive-or-expression  ==>
                exclusive-or-expression  ==>
                    and-expression  ==>
                        equality-expression  ==>
                            relational-expression  ==>
                                shift-expression  ==>
                                    additive-expression  ==>
                                        multiplicative-expression  ==>
                                            pm-expression  ==>
                                                cast-expression  ==>
                                                    unary-expression  ==>
                                                        postfix-expression  ==>
                                                            primary-expression  ==> 
                                                                id-expression  ==>
                                                                    unqualified-id  ==>
                                                                        identifier

And an identifier "is an lvalue if the entity is a function or variable" (5.1/4 "Primary expressions").

So in your example, the expression to the right of the = is an expression that happens to be an lvalue. It could be an rvalue of course, but it doesn't have to be. And there is no mandated lvalue-to-rvalue conversion.

I'm not sure what the value in knowing this is, though.